OBJECTIVES:

To assess trends and behavioral patterns of marijuana and cigarette and/or cigar (ie, smoked tobacco) use among 18- to 22-year-old US young adults who were in or not in college.

METHODS:

Data were from the 2002–2016 National Survey on Drug Use and Health. Past-30-day and past-12-month use of marijuana and smoked tobacco were assessed by college enrollment status. χ2 tests were used to examine within- and between-group differences. Trends were assessed by using logistic regression and relative percentage change (RPC).

RESULTS:

Among both college and noncollege individuals during 2002 to 2016, exclusive marijuana use increased (faster increase among college students; RPC = 166.6 vs 133.7), whereas exclusive smoked tobacco use decreased (faster decrease among college students; RPC = −47.4 vs −43.2). In 2016, 51.6% of noncollege and 46.8% of college individuals reported past-12-month usage of marijuana and/or smoked tobacco products (P < .05). Exclusive marijuana use was higher among college than noncollege individuals, both for past-30-day (11.5% vs 8.6%) and past-12-month use (14.6% vs 10.8%). Exclusive smoked tobacco use was higher among noncollege than college individuals, both for past-30-day (17.7% vs 10.4%) and past-12-month (17.4% vs 12.2%) use (P < .05).

CONCLUSIONS:

Exclusive marijuana use is increasing among young adults overall, whereas exclusive smoked tobacco use is decreasing: faster rates are seen among college students. Exclusive marijuana use is higher among college students, whereas exclusive smoked tobacco use is higher among noncollege individuals. Surveillance of tobacco and marijuana use among young people is important as the policy landscape for these products evolves.

What’s Known on This Subject:

Recreational use of retail marijuana has become legal for adults in 10 states and the District of Columbia. Tobacco and marijuana use commonly co-occur among young people. Marijuana use among college-aged young adults has steadily increased over the past decade.

What This Study Adds:

Exclusive marijuana use is increasing among young adults overall, whereas exclusive smoked tobacco use is decreasing; faster rates are seen among college students. Exclusive marijuana use is higher among college students, whereas exclusive tobacco smoking is higher among noncollege individuals.

Since 2012, recreational use of retail marijuana has become legal for persons ≥21 years of age in 10 states and the District of Columbia.1  Tobacco and marijuana use occur among young people either as separate behaviors or co-occur via devices that can be used for both tobacco and marijuana.27  Specifically, vaporizers are increasingly popular among those who prefer not to inhale smoke.7  Research has shown that tobacco use is associated with initiation of and dependence on other substances, including marijuana.810  Additional studies have shown associations between marijuana use and increased daily tobacco smoking and nicotine dependence.1113 

The adverse health consequences of tobacco use have been well documented, including various cancers, chronic obstructive pulmonary disease, stroke, and heart disease.12,13  In contrast, evidence regarding the health effects of marijuana use is less conclusive14,15 ; however, smoked marijuana, the most common mode of marijuana use,16  contains many of the same toxins, irritants, and carcinogens as tobacco smoke.17  Although evidence shows there can be some therapeutic benefits to marijuana use for some conditions, and some states have approved marijuana for medical use, the US Food and Drug Administration has not recognized or approved the marijuana plant as medicine.14 

At the population level, there is concern regarding the potential for dual use of tobacco products and marijuana because the use of 1 product may increase likelihood of using the other.2,1820  This risk of overlapping modes of use may be especially high among groups with a high peer-to-peer social influence, such as college students.21,22  For example, a 2015 study of never marijuana users revealed that college enrollment served as a predictor of marijuana initiation: among those who had never used marijuana by 12th grade, college students had a 51% higher probability of past-year marijuana use than noncollege young adults.23  Overall, marijuana use among college-aged young adults has steadily increased over the past decade.22  During 2016, nearly 2 in 5 young adults (19–22 years old) reported marijuana use in the past 12 months, and only 30% of young adults perceived regular marijuana use as harmful, the lowest level reached since 1980.22 

Given the aforementioned health risks, as well as the potential for marijuana and tobacco to influence subsequent use of each other, surveillance of these behaviors is important to inform public health practice. To date, some studies have assessed concurrent use of marijuana and tobacco use among young adults; however, studies of marijuana use among college-aged populations have been limited in scope and recency.5,24,25  Most of these studies assessed trends in tobacco and marijuana use before several states began legalization of marijuana, which could have influenced social norms and ensuing patterns of use. To provide recent data on self-reported use of cigarettes and/or cigars (smoked tobacco), marijuana, and concurrent use of both products, we analyzed data over a 15-year period (2002–2016) among a national sample of college-aged (18–22 years old) individuals. Specific objectives in the study included (1) assessing the prevalence and demographic patterns of recent (past-30-day) and past-year use of smoked tobacco and marijuana and (2) assessing their long-term trends among college-aged young adults in the United States.

Data were from the 2002–2016 National Survey on Drug Use and Health (NSDUH), an annual national household-based survey of the civilian, noninstitutionalized US population ≥12 years of age. An independent, multistage area probability sample was used to produce nationally representative estimates. NSDUH participants include residents of households and noninstitutional group quarters (eg, college dormitories) and civilians living on military bases. Selected participants completed the survey in their homes through audio, computer-assisted, self-interview methods, which increase privacy and improve self-report of sensitive behaviors, such as drug and tobacco use. Overall response rates ranged from 61.2% (2014) to 71.9% (2002). Data before 2002 were not included because of differences in survey methodology.

The analyses in this report were restricted to persons aged 18 to 22 years for both the primary study population (college students) and the comparison group (noncollege young adults). College enrollment status was self-reported. College students were defined as those who reported being enrolled in school at the college level (full-time or part-time). Noncollege young adults were defined as those not enrolled in school at the college level, including those still in high school or other grades, high school graduates, school dropouts, or those enrolled in some other type of institution. Sample sizes of college students by year ranged from 3707 (2016) to 6605 (2008). Sampling for any given year of the NSDUH was independent from any other waves of the survey (ie, repeated survey rather than repeated longitudinal observations).

Smoked Tobacco and Marijuana Use

Three specific products were assessed: cigarettes, cigars (big cigars, cigarillos, and/or little cigars), and marijuana (in any form). These product types were collapsed into 2 broad product classes: (1) smoked tobacco (cigarettes and/or cigars) and (2) marijuana (regardless of form used). Cigarettes and cigars were the only tobacco products assessed because other tobacco products were either not captured in the NSDUH (eg, hookah and electronic cigarettes) or had no information on use behavior extending beyond the past 30 days (eg, pipes, smokeless tobacco, and roll-your-own tobacco). The most recent data from National Adult Tobacco Survey show that, among young adults aged 18 to 22 years, current cigarette and/or cigar smokers represented 91% of current smokers of any combustible tobacco.26  Hence, although cigarette or cigar smoking underestimates any smoked tobacco use, this underestimation is minimal.

Participants were asked about use of smoked tobacco and marijuana with separate questions: “How long has it been since you last (smoked a cigarette, smoked any type of cigar, and/or used marijuana or hashish)?” We used responses to these questions to create measures of past-30-day use and past-12-month use for both smoked tobacco and marijuana. We assessed these 2 separate periods to increase sensitivity in capturing occasional users (ie, those whose frequency of use was less than monthly).

We examined 3 patterns of use behavior: (1) overall smoked tobacco or overall marijuana use (use of 1 product regardless of use of the other), (2) exclusive smoked tobacco or exclusive marijuana use (use of 1 product without use of the other), and (3) concurrent (dual) use of smoked tobacco and marijuana (use of both products).

Sociodemographic Characteristics

Assessed sociodemographic characteristics included sex (male or female) and race and/or ethnicity (non-Hispanic white, non-Hispanic African American, Hispanic, and non-Hispanic other [including Asian American, multiracial, American Indian and/or Alaskan native, and Native Hawaiian and/or other Pacific Islander]).

Data were weighted to provide nationally representative estimates and to adjust for differences in the probabilities of selection and nonresponse. Prevalence was computed for overall use, exclusive use, and dual use of smoked tobacco and marijuana among the study population overall and by college enrollment status. Among college and noncollege young adults, prevalence was stratified by sex, race and/or ethnicity, and academic characteristics (full-time or part-time status for college students and academic attainment for noncollege individuals). Statistical differences between college and noncollege individuals were tested with χ2 tests at P < .05. Estimates with relative SEs ≥30% were not reported. Trends during 2002 to 2016 were examined by using relative percentage change (RPC) and binary logistic regression via orthogonal polynomials. Orthogonal linear coefficients were constructed to model trends while controlling for sex and race and/or ethnicity.

Within these analyses, we did not account for the use of blunts because information on blunts was not fully available throughout the study period. Given that some blunt users might not consider or not know that blunts contain tobacco,27  this could lead to underestimates of smoked tobacco use. However, most blunt users in our study population (79.9% and 82.3% for college students and noncollege individuals, respectively) reported using both smoked tobacco and marijuana within the past 12 months; the extent of misclassification was therefore deemed to be minimal. It should be noted that assessing the full extent of misclassification of exclusive tobacco use and marijuana use is difficult because of the overlap of different tobacco use behaviors in the current landscape. For example, there were no data in the NSDUH on whether respondents used marijuana within hookahs or electronic cigarettes. Therefore, the definition of exclusive use should be interpreted within the context of the assessed constructs in this study.

Among adults aged 18 to 22 years overall, the proportion of college students ranged from 44.5% (2002) to 51.2% (2012). During 2016, most college students were female (53.9%), white (53.6%), and enrolled full-time (80.5%), whereas the majority of noncollege young adults were male (56.1%) and white (54.2%), and 44.1% of them reported high school as their highest education attainment. Distributions were similar across study years.

Among college students, the prevalence of overall smoked tobacco use (regardless of marijuana use) in 2002 was 37.9% for past-30-day use and 50.5% for past-12-month use (Tables 1 and 2). In 2016, the corresponding prevalence was 19.1% (past 30 days) and 32.2% (past 12 months). Overall marijuana use (regardless of smoked tobacco use) in 2002 was 18.0% for past-30-day use and 32.7% for past-12-month use. In 2016, the corresponding prevalence was 20.2% (past 30 days) and 34.6% (past 12 months).

TABLE 1

Prevalence of Past 30 Days Smoked Tobacco Use, Marijuana Use, and Overall Tobacco and/or Marijuana Use Among Adults Aged 18 to 22 Years by College Enrollment Status (NSDUH, United States, 2002–2016)

Smoked Tobacco: Overall, % (95% CI)Marijuana Use: Overall, % (95% CI)Smoked Tobacco and/or Marijuana Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 37.9 (36.3–39.5)a 19.1 (17.5–20.8)a↓ 18.0 (16.8–19.3) 20.2 (18.5–21.9)↑ 41.5 (39.8–43.1)a 30.6 (28.7–32.6)a↓ 
 Sex       
  Male 42.1 (39.6–44.6)a,b 25.0 (22.2–27.8)a,b↓ 21.4 (19.4–23.5)b 22.6 (19.8–25.3)b ↑ 46.0 (43.5–48.6)a,b 36.1 (33.0–39.1)a,b↓ 
  Female 34.1 (32.1–36.2)b 14.1 (12.2–16.0)a,b↓ 15.0 (13.5–16.4)b 18.2 (16.1–20.4)b ↑ 37.4 (35.3–39.5)a,b 26.0 (23.5–28.5)a,b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 42.8 (40.9–44.7)a,b 23.5 (21.1–26.0)a,b↓ 21.4 (19.8–23.0)b 22.8 (20.5–25.2)b ↑ 47.0 (45.1–48.9)a,b 35.3 (32.6–38.1)a,b↓ 
  Non-Hispanic African American 24.4 (20.6–28.3)a,b 14.0 (10.5–17.6)a,b↓ 11.2 (8.4–14.1)a,b 23.3 (18.5–28.2)b ↑ 26.6 (22.6–30.5)a,b 29.3 (24.2–34.3)b ↑ 
  Hispanic 26.7 (20.8–32.5)a,b 14.7 (11.1–18.2)a,b↓ 9.5 (6.5–12.6)b 16.1 (12.3–19.9)b ↑ 28.9 (23.0–34.8)a,b 24.9 (20.6–29.2)a↓ 
  Non-Hispanic other 31.4 (25.3–37.5)a,b 12.9 (8.9–16.8)a,b↓ 11.0 (7.4–14.5)b 12.7 (8.7–16.7)b 33.5 (27.3–39.6)a,b 21.3 (16.3–26.3)a,b↓ 
 Status       
  Full-time 36.9 (35.1–38.6) 19.3 (17.4–21.1)↓ 18.1 (16.7–19.4) 20.2 (18.3–22.0)↑ 40.7 (38.9–42.5) 30.8 (28.7–33.0)↓ 
  Part-time 43.5 (39.1–47.8) 18.6 (15.0–22.2)↓ 17.8 (14.5–21.0) 20.6 (16.5–24.6)↑ 45.8 (41.4–50.2) 29.7 (25.4–34.1)↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 49.3 (47.7–50.9)a 30.7 (29.0–32.5)a↓ 18.9 (17.7–20.1) 21.6 (20.1–23.2)↑ 52.5 (50.9–54.1)a 39.3 (37.5–41.2)a↓ 
 Sex       
  Male 54.4 (52.2–56.6)a,b 34.6 (32.1–37.1)a↓ 22.7 (20.9–24.5) 25.1 (22.8–27.4)↑ 58.1 (55.9–60.3)a 43.9 (41.3–46.5)a↓ 
  Female 43.3 (41.1–45.4)a,b 25.8 (23.4–28.1)a↓ 14.4 (13.0–15.9) 17.2 (15.2–19.2)↑ 45.9 (43.8–48.1)a 33.5 (30.9–36.1)a↓ 
 Race and/or ethnicity       
  Non-Hispanic white 57.7 (55.8–59.5)a,b 36.7 (34.2–39.2)a↓ 22.2 (20.6–23.8) 22.6 (20.4–24.8) 60.7 (58.9–62.6)a 44.4 (41.8–46.9)a↓ 
  Non-Hispanic African American 37.1 (33.4–40.8)a,b 24.2 (20.6–27.8)a↓ 17.0 (14.2–19.7)a 22.8 (19.2–26.4)↑ 42.2 (38.5–46.0)a 35.0 (30.9–39.0)↓ 
  Hispanic 36.4 (32.7–40.1)a,b 22.0 (18.5–25.5)a↓ 12.3 (9.9–14.7) 19.6 (16.2–23.0)↑ 38.9 (35.1–42.6)a 31.7 (27.7–35.6)a↓ 
  Non-Hispanic other 48.1 (40.6–55.7)a,b 27.3 (21.6–33.1)a↓ 17.0 (11.4–22.5) 18.2 (13.5–22.8) 50.8 (43.3–58.3)a 35.0 (28.8–41.2)a↓ 
 Education       
  Less than high school 50.2 (47.7–52.6)b 29.1 (26.1–32.1)↓ 19.9 (18.1–21.8) 21.0 (18.2–23.8) 53.1 (50.7–55.6) 37.2 (34.0–40.5)↓ 
  High school 48.6 (46.2–51.0)b 33.8 (31.1–36.6)↓ 18.4 (16.5–20.2) 20.9 (18.5–23.2)↑ 52.1 (49.7–54.5) 42.2 (39.3–45.1)↓ 
  Some college or more 48.6 (44.8–52.3)b 27.8 (24.5–31.2)↓ 17.1 (14.2–19.9) 23.5 (20.4–26.6)↑ 51.6 (47.9–55.4) 37.3 (33.7–40.9)↓ 
Smoked Tobacco: Overall, % (95% CI)Marijuana Use: Overall, % (95% CI)Smoked Tobacco and/or Marijuana Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 37.9 (36.3–39.5)a 19.1 (17.5–20.8)a↓ 18.0 (16.8–19.3) 20.2 (18.5–21.9)↑ 41.5 (39.8–43.1)a 30.6 (28.7–32.6)a↓ 
 Sex       
  Male 42.1 (39.6–44.6)a,b 25.0 (22.2–27.8)a,b↓ 21.4 (19.4–23.5)b 22.6 (19.8–25.3)b ↑ 46.0 (43.5–48.6)a,b 36.1 (33.0–39.1)a,b↓ 
  Female 34.1 (32.1–36.2)b 14.1 (12.2–16.0)a,b↓ 15.0 (13.5–16.4)b 18.2 (16.1–20.4)b ↑ 37.4 (35.3–39.5)a,b 26.0 (23.5–28.5)a,b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 42.8 (40.9–44.7)a,b 23.5 (21.1–26.0)a,b↓ 21.4 (19.8–23.0)b 22.8 (20.5–25.2)b ↑ 47.0 (45.1–48.9)a,b 35.3 (32.6–38.1)a,b↓ 
  Non-Hispanic African American 24.4 (20.6–28.3)a,b 14.0 (10.5–17.6)a,b↓ 11.2 (8.4–14.1)a,b 23.3 (18.5–28.2)b ↑ 26.6 (22.6–30.5)a,b 29.3 (24.2–34.3)b ↑ 
  Hispanic 26.7 (20.8–32.5)a,b 14.7 (11.1–18.2)a,b↓ 9.5 (6.5–12.6)b 16.1 (12.3–19.9)b ↑ 28.9 (23.0–34.8)a,b 24.9 (20.6–29.2)a↓ 
  Non-Hispanic other 31.4 (25.3–37.5)a,b 12.9 (8.9–16.8)a,b↓ 11.0 (7.4–14.5)b 12.7 (8.7–16.7)b 33.5 (27.3–39.6)a,b 21.3 (16.3–26.3)a,b↓ 
 Status       
  Full-time 36.9 (35.1–38.6) 19.3 (17.4–21.1)↓ 18.1 (16.7–19.4) 20.2 (18.3–22.0)↑ 40.7 (38.9–42.5) 30.8 (28.7–33.0)↓ 
  Part-time 43.5 (39.1–47.8) 18.6 (15.0–22.2)↓ 17.8 (14.5–21.0) 20.6 (16.5–24.6)↑ 45.8 (41.4–50.2) 29.7 (25.4–34.1)↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 49.3 (47.7–50.9)a 30.7 (29.0–32.5)a↓ 18.9 (17.7–20.1) 21.6 (20.1–23.2)↑ 52.5 (50.9–54.1)a 39.3 (37.5–41.2)a↓ 
 Sex       
  Male 54.4 (52.2–56.6)a,b 34.6 (32.1–37.1)a↓ 22.7 (20.9–24.5) 25.1 (22.8–27.4)↑ 58.1 (55.9–60.3)a 43.9 (41.3–46.5)a↓ 
  Female 43.3 (41.1–45.4)a,b 25.8 (23.4–28.1)a↓ 14.4 (13.0–15.9) 17.2 (15.2–19.2)↑ 45.9 (43.8–48.1)a 33.5 (30.9–36.1)a↓ 
 Race and/or ethnicity       
  Non-Hispanic white 57.7 (55.8–59.5)a,b 36.7 (34.2–39.2)a↓ 22.2 (20.6–23.8) 22.6 (20.4–24.8) 60.7 (58.9–62.6)a 44.4 (41.8–46.9)a↓ 
  Non-Hispanic African American 37.1 (33.4–40.8)a,b 24.2 (20.6–27.8)a↓ 17.0 (14.2–19.7)a 22.8 (19.2–26.4)↑ 42.2 (38.5–46.0)a 35.0 (30.9–39.0)↓ 
  Hispanic 36.4 (32.7–40.1)a,b 22.0 (18.5–25.5)a↓ 12.3 (9.9–14.7) 19.6 (16.2–23.0)↑ 38.9 (35.1–42.6)a 31.7 (27.7–35.6)a↓ 
  Non-Hispanic other 48.1 (40.6–55.7)a,b 27.3 (21.6–33.1)a↓ 17.0 (11.4–22.5) 18.2 (13.5–22.8) 50.8 (43.3–58.3)a 35.0 (28.8–41.2)a↓ 
 Education       
  Less than high school 50.2 (47.7–52.6)b 29.1 (26.1–32.1)↓ 19.9 (18.1–21.8) 21.0 (18.2–23.8) 53.1 (50.7–55.6) 37.2 (34.0–40.5)↓ 
  High school 48.6 (46.2–51.0)b 33.8 (31.1–36.6)↓ 18.4 (16.5–20.2) 20.9 (18.5–23.2)↑ 52.1 (49.7–54.5) 42.2 (39.3–45.1)↓ 
  Some college or more 48.6 (44.8–52.3)b 27.8 (24.5–31.2)↓ 17.1 (14.2–19.9) 23.5 (20.4–26.6)↑ 51.6 (47.9–55.4) 37.3 (33.7–40.9)↓ 

↑ indicates prevalence linearly increased during 2002–2016 (P < .05), and ↓ indicates prevalence linearly decreased during 2002–2016 (P < .05). Overall use of smoked tobacco was defined as use of cigarettes and/or cigars (big cigars, cigarillos, and/or little cigars) regardless of marijuana use. Overall use of marijuana was defined as use of marijuana (regardless of the mode of consumption) regardless of smoked tobacco use. CI, confidence interval.

a

Results are significantly different between college students and noncollege individuals (P < .05).

b

Responses vary significantly (P < .05) within the assessed demographic subgroups.

TABLE 2

Prevalence of Past 12 Months Smoked Tobacco Use, Marijuana Use, and Overall Tobacco and/or Marijuana Use Among Adults Aged 18 to 22 Years by College Enrollment Status (NSDUH, United States, 2002–2016)

Smoked Tobacco: Overall, % (95% CI)Marijuana Use: Overall, % (95% CI)Smoked Tobacco and/or Marijuana Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 50.5 (48.8–52.2)a 32.2 (30.2–34.2)a↓ 32.7 (31.1–34.2) 34.6 (32.6–36.6)↑ 55.9 (54.2–57.5)a 46.8 (44.7–48.9)a↓ 
 Sex       
  Male 55.8 (53.3–58.3)a,b 39.9 (36.8–43.0)a,b↓ 35.5 (33.1–38.0) 35.9 (32.9–39.0)↑ 60.2 (57.7–62.7)b 51.7 (48.5–54.9)a,b↓ 
  Female 45.8 (43.6–48.0)a,b 25.6 (23.2–28.1)a,b↓ 30.1 (28.1–32.1)a,b 33.5 (30.8–36.1)a↑ 52.0 (49.8–54.2)ab 42.6 (39.8–45.3)b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 56.2 (54.4–58.1)a,b 39.0 (36.3–41.8)a,b↓ 36.7 (34.9–38.6)b 38.7 (35.9–41.4)b↑ 61.6 (59.8–63.5)a,b 53.5 (50.7–56.2)a,b↓ 
  Non-Hispanic African American 32.2 (28.1–36.4)a,b 19.3 (15.2–23.4)a,b↓ 21.9 (18.2–25.6)a,b 35.0 (29.7–40.2)b↑ 38.6 (34.2–42.9)a,b 40.9 (35.5–46.2)b↑ 
  Hispanic 40.3 (33.8–46.8)b 27.8 (23.3–32.2)b ↓ 23.3 (18.2–28.4)b 29.8 (25.3–34.3)b↑ 45.5 (39.0–52.1)b 41.3 (36.5–46.1)b↓ 
  Non-Hispanic other 43.2 (36.7–49.7)a,b 23.2 (18.0–28.4)a,b↓ 26.5 (20.9–32.1)b 24.6 (19.4–29.7)b 47.1 (40.5–53.7)a,b 32.9 (27.1–38.6)a,b↓ 
 Status       
  Full-time 50.0 (48.2–51.8) 33.1 (30.9–35.4)↓ 33.0 (31.3–34.7) 35.6 (33.3–37.9)↑ 55.5 (53.7–57.4) 48.2 (45.8–50.5)b↓ 
  Part-time 53.3 (48.9–57.6) 28.3 (24.1–32.6)↓ 30.9 (26.9–34.8) 30.5 (26.0–35.0)↑ 57.6 (53.3–62.0) 41.0 (36.3–45.7)b↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 58.1 (56.6–59.7)a 40.8 (38.9–42.7)a↓ 31.7 (30.2–33.1) 34.2 (32.4–36.0)↑ 62.4 (60.9–64.0)a 51.6 (49.7–53.5)a↓ 
 Sex       
  Male 63.7 (61.5–65.8)a,b 46.3 (43.7–48.9)a,b↓ 35.8 (33.7–37.9)b 37.9 (35.4–40.4)b ↑ 68.0 (65.9–70.1)a,b 56.2 (53.6–58.8)a,b↓ 
  Female 51.7 (49.5–53.9)a,b 33.7 (31.2–36.3)a,b↓ 26.9 (24.9–28.8)a,b 29.5 (27.0–32.0)a,b↑ 56.0 (53.8–58.2)a,b 45.7 (43.0–48.5)b ↓ 
 Race and/or ethnicity       
  Non-Hispanic white 66.9 (65.1–68.7)a,b 48.4 (45.8–51.0)a,b↓ 36.4 (34.6–38.3)b 37.0 (34.5–39.5)b 70.8 (69.1–72.5)a,b 58.3 (55.8–60.9)a,b↓ 
  Non-Hispanic African American 44.9 (41.1–48.7)a,b 31.3 (27.3–35.2)a,b↓ 28.8 (25.2–32.3)a,b 33.7 (29.7–37.8)b ↑ 51.7 (47.8–55.5)a,b 45.6 (41.3–49.9)b 
  Hispanic 45.3 (41.4–49.2)b 30.8 (26.9–34.7)b↓ 21.5 (18.3–24.7)b 29.2 (25.4–33.0)b ↑ 48.9 (45.0–52.9)b 42.2 (38.0–46.4)b↓ 
  Non-Hispanic other 55.6 (48.1–63.1)a,b 35.6 (29.3–41.9)a,b↓ 32.4 (25.2–39.5)b 30.2 (24.2–36.2)b 59.8 (52.3–67.3)a,b 44.1 (37.5–50.7)a,b↓ 
 Education       
  Less than high school 59.0 (56.6–61.4) 35.5 (32.4–38.7)b↓ 31.3 (29.1–33.5) 30.9 (27.8–34.0)b 62.2 (59.8–64.6) 46.5 (43.2–49.9)b↓ 
  High school 56.6 (54.2–59.0) 45.1 (42.2–48.0)b↓ 31.5 (29.2–33.7) 34.8 (32.0–37.6)b↑ 61.9 (59.5–64.2) 54.9 (52.0–57.8)b↓ 
  Some college or more 59.6 (55.9–63.3) 40.2 (36.6–43.8)b↓ 33.5 (29.8–37.1) 36.9 (33.4–40.5)b↑ 64.8 (61.1–68.4) 52.3 (48.6–56.0)b↓ 
Smoked Tobacco: Overall, % (95% CI)Marijuana Use: Overall, % (95% CI)Smoked Tobacco and/or Marijuana Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 50.5 (48.8–52.2)a 32.2 (30.2–34.2)a↓ 32.7 (31.1–34.2) 34.6 (32.6–36.6)↑ 55.9 (54.2–57.5)a 46.8 (44.7–48.9)a↓ 
 Sex       
  Male 55.8 (53.3–58.3)a,b 39.9 (36.8–43.0)a,b↓ 35.5 (33.1–38.0) 35.9 (32.9–39.0)↑ 60.2 (57.7–62.7)b 51.7 (48.5–54.9)a,b↓ 
  Female 45.8 (43.6–48.0)a,b 25.6 (23.2–28.1)a,b↓ 30.1 (28.1–32.1)a,b 33.5 (30.8–36.1)a↑ 52.0 (49.8–54.2)ab 42.6 (39.8–45.3)b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 56.2 (54.4–58.1)a,b 39.0 (36.3–41.8)a,b↓ 36.7 (34.9–38.6)b 38.7 (35.9–41.4)b↑ 61.6 (59.8–63.5)a,b 53.5 (50.7–56.2)a,b↓ 
  Non-Hispanic African American 32.2 (28.1–36.4)a,b 19.3 (15.2–23.4)a,b↓ 21.9 (18.2–25.6)a,b 35.0 (29.7–40.2)b↑ 38.6 (34.2–42.9)a,b 40.9 (35.5–46.2)b↑ 
  Hispanic 40.3 (33.8–46.8)b 27.8 (23.3–32.2)b ↓ 23.3 (18.2–28.4)b 29.8 (25.3–34.3)b↑ 45.5 (39.0–52.1)b 41.3 (36.5–46.1)b↓ 
  Non-Hispanic other 43.2 (36.7–49.7)a,b 23.2 (18.0–28.4)a,b↓ 26.5 (20.9–32.1)b 24.6 (19.4–29.7)b 47.1 (40.5–53.7)a,b 32.9 (27.1–38.6)a,b↓ 
 Status       
  Full-time 50.0 (48.2–51.8) 33.1 (30.9–35.4)↓ 33.0 (31.3–34.7) 35.6 (33.3–37.9)↑ 55.5 (53.7–57.4) 48.2 (45.8–50.5)b↓ 
  Part-time 53.3 (48.9–57.6) 28.3 (24.1–32.6)↓ 30.9 (26.9–34.8) 30.5 (26.0–35.0)↑ 57.6 (53.3–62.0) 41.0 (36.3–45.7)b↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 58.1 (56.6–59.7)a 40.8 (38.9–42.7)a↓ 31.7 (30.2–33.1) 34.2 (32.4–36.0)↑ 62.4 (60.9–64.0)a 51.6 (49.7–53.5)a↓ 
 Sex       
  Male 63.7 (61.5–65.8)a,b 46.3 (43.7–48.9)a,b↓ 35.8 (33.7–37.9)b 37.9 (35.4–40.4)b ↑ 68.0 (65.9–70.1)a,b 56.2 (53.6–58.8)a,b↓ 
  Female 51.7 (49.5–53.9)a,b 33.7 (31.2–36.3)a,b↓ 26.9 (24.9–28.8)a,b 29.5 (27.0–32.0)a,b↑ 56.0 (53.8–58.2)a,b 45.7 (43.0–48.5)b ↓ 
 Race and/or ethnicity       
  Non-Hispanic white 66.9 (65.1–68.7)a,b 48.4 (45.8–51.0)a,b↓ 36.4 (34.6–38.3)b 37.0 (34.5–39.5)b 70.8 (69.1–72.5)a,b 58.3 (55.8–60.9)a,b↓ 
  Non-Hispanic African American 44.9 (41.1–48.7)a,b 31.3 (27.3–35.2)a,b↓ 28.8 (25.2–32.3)a,b 33.7 (29.7–37.8)b ↑ 51.7 (47.8–55.5)a,b 45.6 (41.3–49.9)b 
  Hispanic 45.3 (41.4–49.2)b 30.8 (26.9–34.7)b↓ 21.5 (18.3–24.7)b 29.2 (25.4–33.0)b ↑ 48.9 (45.0–52.9)b 42.2 (38.0–46.4)b↓ 
  Non-Hispanic other 55.6 (48.1–63.1)a,b 35.6 (29.3–41.9)a,b↓ 32.4 (25.2–39.5)b 30.2 (24.2–36.2)b 59.8 (52.3–67.3)a,b 44.1 (37.5–50.7)a,b↓ 
 Education       
  Less than high school 59.0 (56.6–61.4) 35.5 (32.4–38.7)b↓ 31.3 (29.1–33.5) 30.9 (27.8–34.0)b 62.2 (59.8–64.6) 46.5 (43.2–49.9)b↓ 
  High school 56.6 (54.2–59.0) 45.1 (42.2–48.0)b↓ 31.5 (29.2–33.7) 34.8 (32.0–37.6)b↑ 61.9 (59.5–64.2) 54.9 (52.0–57.8)b↓ 
  Some college or more 59.6 (55.9–63.3) 40.2 (36.6–43.8)b↓ 33.5 (29.8–37.1) 36.9 (33.4–40.5)b↑ 64.8 (61.1–68.4) 52.3 (48.6–56.0)b↓ 

↑ indicates prevalence linearly increased during 2002–2016 (P < .05), and ↓ indicates prevalence linearly decreased during 2002–2016 (P < .05). Overall use of smoked tobacco was defined as use of cigarettes and/or cigars (big cigars, cigarillos, and/or little cigars) regardless of marijuana use. Overall use of marijuana was defined as use of marijuana (regardless of the mode of consumption) regardless of smoked tobacco use. CI, confidence interval.

a

Results significantly differ between college students and noncollege individuals (P < .05).

b

Responses vary significantly (P < .05) within the assessed demographic subgroups.

Among noncollege young adults compared with college students, significantly higher prevalence was reported for overall smoked tobacco use, as well as overall use of smoked tobacco and/or marijuana for both past-30-day and past-12-month use, in 2002 and 2016 (Tables 1 and 2).

Among college students, exclusive tobacco smoking declined during 2002 to 2016, from 23.5% to 10.4% (RPC = −55.7) for past-30-day use and from 23.2% to 12.2% (RPC = −47.4) for past-12-month use (Tables 3 and 4, Fig 1, Supplemental Fig 2). Declines were significant within all population subgroups assessed. During 2016, prevalence was significantly higher among male than among female college students for both past-30-day use (13.5% vs 7.8%) and past-12-month use (15.8% vs 9.1%). By race and/or ethnicity, prevalence was highest among white college students for both past-30-day (12.5%) and past-12-month (14.8%) use (all P < .05).

TABLE 3

Prevalence of Past 30 Days Exclusive Smoked Tobacco Use, Marijuana Use, and Dual Use Among Adults Aged 18 to 22 Years, by College Enrollment Status (NSDUH, United States, 2002–2016)

Smoked Tobacco: Exclusive, % (95% CI)Marijuana Use: Exclusive, % (95% CI)Dual Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 23.5 (22.0–24.9)a 10.4 (9.1–11.7)a↓ 3.6 (3.0–4.2) 11.5 (10.1–12.9)a↑ 14.4 (13.3–15.6) 8.7 (7.5–9.9)a↓ 
 Sex       
  Male 24.6 (22.4–26.8)a 13.5 (11.3–15.6)a,b↓ 3.9 (3.1–4.8) 11.0 (9.0–13.0)↑ 17.5 (15.6–19.4)b 11.6 (9.4–13.7)a,b↓ 
  Female 22.5 (20.6–24.3)a 7.8 (6.2–9.3)a,b↓ 3.3 (2.6–4.0) 11.9 (10.0–13.8)a↑ 11.7 (10.3–13.0)b 6.3 (5.1–7.6)a,b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 25.7 (24.0–27.3)a,b 12.5 (10.6–14.4)a,b↓ 4.3 (3.5–5.0)a,b 11.8 (9.9–13.7)a↑ 17.1 (15.6–18.6)b 11.0 (9.3–12.8)a,b↓ 
  Non-Hispanic African American 15.4 (12.1–18.6)a,b 5.9 (3.6–8.3)a,b↓ 2.1 (1.0–3.3)a,b 15.3 (10.9–19.6)↑ 9.1 (6.5–11.7)b 8.1 (5.3–10.9)b 
  Hispanic 19.3 (13.8–24.9)a,b 8.8 (6.1–11.5)b↓ — 10.2 (7.2–13.3)↑ 7.3 (4.6–10.1)b 5.9 (3.3–8.4)a,b 
  Non-Hispanic other 22.5 (16.9–28.2)a,b 8.6 (5.2–12.0)a,b↓ — 8.4 (4.9–11.9)↑ 8.9 (5.6–12.2)b 4.3 (2.2–6.5)a,b↓ 
 Status       
  Full-time 28.0 (24.1–32.0)b 9.2 (6.6–11.7)↓ 2.3 (1.3–3.4)b 11.1 (7.8–14.4)↑ 15.4 (12.3–18.6) 9.4 (6.7–12.2)↓ 
  Part-time 22.6 (21.1–24.2)b 10.7 (9.2–12.2)↓ 3.8 (3.2–4.5)b 11.6 (10.1–13.1)↑ 14.2 (13.0–15.5) 8.6 (7.2–9.9)↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 33.6 (32.2–35.1)a 17.7 (16.3–19.1)a↓ 3.2 (2.7–3.8) 8.6 (7.5–9.6)a↑ 15.7 (14.6–16.8) 13.0 (11.7–14.3)a↓ 
 Sex       
  Male 35.4 (33.3–37.5)a,b 18.8 (16.8–20.7)a↓ 3.7 (2.8–4.6) 9.3 (7.8–10.8)↑ 19.0 (17.3–20.6)b 15.8 (13.9–17.8)a,b↓ 
  Female 31.5 (29.5–33.5)a,b 16.4 (14.3–18.4)a↓ 2.6 (2.0–3.3) 7.7 (6.2–9.2)a↑ 11.8 (10.4–13.1)b 9.4 (7.9–10.9)a,b 
 Race and/or ethnicity       
  Non-Hispanic white 38.6 (36.7–40.4)a,b 21.8 (19.7–23.9)a,b↓ 3.1 (2.4–3.7)a,b 7.7 (6.3–9.1)a↑ 19.1 (17.6–20.6)b 14.9 (13.1–16.8)a,b↓ 
  Non-Hispanic African American 25.3 (21.9–28.6)a,b 12.1 (9.4–14.8)a,b↓ 5.1 (3.6–6.7)a,b 10.7 (8.0–13.5)↑ 11.8 (9.4–14.2)b 12.1 (9.4–14.8)b 
  Hispanic 26.6 (23.1–30.0)a,b 12.1 (9.4–14.8)b↓ — 9.6 (7.2–12.1)↑ 9.8 (7.8–11.9)b 9.9 (7.3–12.6)a,b↑ 
  Non-Hispanic other 33.8 (26.7–41.0)a,b 16.8 (11.9–21.7)a,b↓ — 7.6 (4.4–10.8)↑ 14.3 (8.9–19.7)b 10.5 (6.9–14.2)a,b 
 Education       
  Less than high school 33.2 (30.9–35.5) 16.3 (14.0–18.6)b↓ 3.0 (2.2–3.8) 8.1 (6.2–10.0)↑ 16.9 (15.2–18.7)↓ 12.8 (10.5–15.1) 
  High school 33.7 (31.5–36.0) 21.3 (18.9–23.7)b↓ 3.5 (2.5–4.4) 8.3 (6.7–10.0)↑ 14.9 (13.3–16.5) 12.5 (10.6–14.4) 
  Some college or more 34.5 (30.9–38.1) 13.8 (11.2–16.4)b↓ 3.1 (1.9–4.3) 9.5 (7.4–11.6)↑ 14.0 (11.3–16.6) 13.9 (11.4–16.6) 
Smoked Tobacco: Exclusive, % (95% CI)Marijuana Use: Exclusive, % (95% CI)Dual Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 23.5 (22.0–24.9)a 10.4 (9.1–11.7)a↓ 3.6 (3.0–4.2) 11.5 (10.1–12.9)a↑ 14.4 (13.3–15.6) 8.7 (7.5–9.9)a↓ 
 Sex       
  Male 24.6 (22.4–26.8)a 13.5 (11.3–15.6)a,b↓ 3.9 (3.1–4.8) 11.0 (9.0–13.0)↑ 17.5 (15.6–19.4)b 11.6 (9.4–13.7)a,b↓ 
  Female 22.5 (20.6–24.3)a 7.8 (6.2–9.3)a,b↓ 3.3 (2.6–4.0) 11.9 (10.0–13.8)a↑ 11.7 (10.3–13.0)b 6.3 (5.1–7.6)a,b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 25.7 (24.0–27.3)a,b 12.5 (10.6–14.4)a,b↓ 4.3 (3.5–5.0)a,b 11.8 (9.9–13.7)a↑ 17.1 (15.6–18.6)b 11.0 (9.3–12.8)a,b↓ 
  Non-Hispanic African American 15.4 (12.1–18.6)a,b 5.9 (3.6–8.3)a,b↓ 2.1 (1.0–3.3)a,b 15.3 (10.9–19.6)↑ 9.1 (6.5–11.7)b 8.1 (5.3–10.9)b 
  Hispanic 19.3 (13.8–24.9)a,b 8.8 (6.1–11.5)b↓ — 10.2 (7.2–13.3)↑ 7.3 (4.6–10.1)b 5.9 (3.3–8.4)a,b 
  Non-Hispanic other 22.5 (16.9–28.2)a,b 8.6 (5.2–12.0)a,b↓ — 8.4 (4.9–11.9)↑ 8.9 (5.6–12.2)b 4.3 (2.2–6.5)a,b↓ 
 Status       
  Full-time 28.0 (24.1–32.0)b 9.2 (6.6–11.7)↓ 2.3 (1.3–3.4)b 11.1 (7.8–14.4)↑ 15.4 (12.3–18.6) 9.4 (6.7–12.2)↓ 
  Part-time 22.6 (21.1–24.2)b 10.7 (9.2–12.2)↓ 3.8 (3.2–4.5)b 11.6 (10.1–13.1)↑ 14.2 (13.0–15.5) 8.6 (7.2–9.9)↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 33.6 (32.2–35.1)a 17.7 (16.3–19.1)a↓ 3.2 (2.7–3.8) 8.6 (7.5–9.6)a↑ 15.7 (14.6–16.8) 13.0 (11.7–14.3)a↓ 
 Sex       
  Male 35.4 (33.3–37.5)a,b 18.8 (16.8–20.7)a↓ 3.7 (2.8–4.6) 9.3 (7.8–10.8)↑ 19.0 (17.3–20.6)b 15.8 (13.9–17.8)a,b↓ 
  Female 31.5 (29.5–33.5)a,b 16.4 (14.3–18.4)a↓ 2.6 (2.0–3.3) 7.7 (6.2–9.2)a↑ 11.8 (10.4–13.1)b 9.4 (7.9–10.9)a,b 
 Race and/or ethnicity       
  Non-Hispanic white 38.6 (36.7–40.4)a,b 21.8 (19.7–23.9)a,b↓ 3.1 (2.4–3.7)a,b 7.7 (6.3–9.1)a↑ 19.1 (17.6–20.6)b 14.9 (13.1–16.8)a,b↓ 
  Non-Hispanic African American 25.3 (21.9–28.6)a,b 12.1 (9.4–14.8)a,b↓ 5.1 (3.6–6.7)a,b 10.7 (8.0–13.5)↑ 11.8 (9.4–14.2)b 12.1 (9.4–14.8)b 
  Hispanic 26.6 (23.1–30.0)a,b 12.1 (9.4–14.8)b↓ — 9.6 (7.2–12.1)↑ 9.8 (7.8–11.9)b 9.9 (7.3–12.6)a,b↑ 
  Non-Hispanic other 33.8 (26.7–41.0)a,b 16.8 (11.9–21.7)a,b↓ — 7.6 (4.4–10.8)↑ 14.3 (8.9–19.7)b 10.5 (6.9–14.2)a,b 
 Education       
  Less than high school 33.2 (30.9–35.5) 16.3 (14.0–18.6)b↓ 3.0 (2.2–3.8) 8.1 (6.2–10.0)↑ 16.9 (15.2–18.7)↓ 12.8 (10.5–15.1) 
  High school 33.7 (31.5–36.0) 21.3 (18.9–23.7)b↓ 3.5 (2.5–4.4) 8.3 (6.7–10.0)↑ 14.9 (13.3–16.5) 12.5 (10.6–14.4) 
  Some college or more 34.5 (30.9–38.1) 13.8 (11.2–16.4)b↓ 3.1 (1.9–4.3) 9.5 (7.4–11.6)↑ 14.0 (11.3–16.6) 13.9 (11.4–16.6) 

↑ indicates prevalence linearly increased during 2002 to 2016 (P < .05), and ↓ indicates prevalence linearly decreased during 2002 to 2016 (P < .05). Exclusive use of smoked tobacco was defined as use of cigarettes and/or cigars (big cigars, cigarillos, and/or little cigars) without using marijuana. Exclusive use of marijuana was defined as use of marijuana (regardless of the mode of consumption) without using smoked tobacco. CI, confidence interval; —, estimates suppressed because of relative SE ≥30%.

a

Results significantly differ between college students and noncollege individuals (P < .05).

b

Responses vary significantly (P < .05) within the assessed demographic subgroups.

TABLE 4

Prevalence of Past 12 Months Exclusive Smoked Tobacco Use, Marijuana Use, and Dual Use Among Adults Aged 18 to 22 Years by College Enrollment Status (NSDUH, United States, 2002–2016)

Smoked Tobacco: Exclusive, % (95% CI)Marijuana: Exclusive, % (95% CI)Dual Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 23.2 (21.7–24.6)a 12.2 (10.8–13.5)a↓ 5.5 (4.8–6.2) 14.6 (13.1–16.1)a↑ 27.2 (25.7–28.7) 20.0 (18.3–21.7)a↓ 
 Sex       
  Male 24.6 (22.3–26.8)a 15.8 (13.6–18.0)b↓ 4.5 (3.5–5.4)b 11.9 (9.8–13.9)b↑ 31.1 (28.7–33.4)b 24.0 (21.3–26.8)a,b↓ 
  Female 21.9 (20.1–23.7)a 9.1 (7.5–10.7)b↓ 6.4 (5.3–7.4)a,b 16.9 (14.8–19.0)b↑ 23.7 (21.9–25.6)b 16.5 (14.4–18.7)b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 24.8 (23.2–26.5)a,b 14.8 (12.8–16.8)a,b↓ 5.5 (4.7–6.4)a 14.4 (12.4–16.4)a,b↑ 31.2 (29.4–33.1)b 24.3 (21.8–26.7)b↓ 
  Non-Hispanic African American 16.6 (13.4–19.9)ab, 5.9 (3.6–8.2)a,b↓ 6.9 (4.7–9.1) 21.6 (16.9–26.2)a,b↑ 15.0 (11.8–18.2)a,b 13.4 (9.8–17.0)a,b 
  Hispanic 22.1 (16.0–28.2) 11.5 (8.6–14.4)b↓ 5.0 (2.6–7.5) 13.7 (10.5–16.8)b↑ 18.3 (13.7–22.9)b 16.1 (12.2–20.1)b 
  Non-Hispanic other 20.5 (15.0–26.0) 8.3 (5.0–11.6)a,b↓ — 9.7 (6.5–12.9)b↑ 22.8 (17.4–28.1)b 14.9 (10.5–19.3)b↓ 
 Status       
  Full-time 26.6 (22.5–30.6) 10.5 (7.8–13.2)↓ 4.4 (2.9–5.9) 12.7 (9.3–16.0)↑ 26.5 (22.7–30.3) 17.8 (14.1–21.6)↓ 
  Part-time 22.6 (21.0–24.1) 12.6 (11.1–14.1)↓ 5.7 (4.9–6.5) 15.1 (13.4–16.7)↑ 27.3 (25.7–28.9) 20.5 (18.6–22.5)↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 30.7 (29.2–32.1)a 17.4 (16.0–18.9)a ↓ 4.6 (3.9–5.3) 10.8 (9.6–12.0)a↑ 27.1 (25.7–28.4) 23.4 (21.8–25.0)a↓ 
 Sex       
  Male 32.1 (30.0–34.1)a,b 18.3 (16.3–20.3)↓ 4.7 (3.7–5.7) 9.9 (8.3–11.4)↑ 31.1 (29.1–33.1)b 28.1 (25.7–30.4)a,b↓ 
  Female 29.0 (27.1–31.0)a,b 16.3 (14.3–18.3)↓ 4.5 (3.6–5.4)a 12.0 (10.2–13.8)↑ 22.3 (20.5–24.2)b 17.4 (15.4–19.4)b 
 Race and/or ethnicity       
  Non-Hispanic white 34.3 (32.5–36.0)a,b 21.4 (19.3–23.5)a,b↓ 4.1 (3.3–4.9)a,b 9.9 (8.3–11.5)a,b↑ 32.4 (30.6–34.1)b 27.0 (24.7–29.3)b↓ 
  Non-Hispanic African American 22.8 (19.5–26.0)a,b 11.9 (9.2–14.6)a,b↓ 7.6 (5.7–9.6)b 14.3 (11.4–17.3)a,b↑ 21.1 (17.9–24.3)a,b 19.4 (16.0–22.8)a,b 
  Hispanic 27.4 (23.9–30.9)b 13.0 (10.2–15.8)b↓ 4.0 (2.2–5.8)b 11.3 (8.7–13.9)b↑ 17.5 (14.6–20.4)b 17.9 (14.6–21.2)b↑ 
  Non-Hispanic other 27.4 (20.8–34.0)b 13.8 (9.5–18.2)a,b↓ 4.8 (2.0–7.7)b 8.4 (5.2–11.6)b↑ 27.5 (20.6–34.5)b 21.8 (16.4–27.3)b 
 Education       
  Less than high school 30.8 (28.5–33.0) 15.7 (13.4–18.0)b↓ 3.7 (2.7–4.6)b 10.9 (8.8–13.1)↑ 27.6 (25.5–29.8) 19.9 (17.2–22.6)b↓ 
  High school 30.3 (28.2–32.5) 20.1 (17.7–22.4)b↓ 5.4 (4.2–6.7)b 9.8 (8.1–11.6)↑ 26.0 (23.9–28.1) 25.0 (22.4–27.6)b 
  Some college or higher 31.3 (27.9–34.7) 15.4 (12.7–18.1)b↓ 5.2 (3.6–6.9)b 12.1 (9.7–14.4)↑ 28.2 (24.7–31.7) 24.8 (21.6–28.0)b 
Smoked Tobacco: Exclusive, % (95% CI)Marijuana: Exclusive, % (95% CI)Dual Use, % (95% CI)
200220162002201620022016
College students n = 5131 n = 3707 n = 5131 n = 3707 n = 5131 n = 3707 
 Overall 23.2 (21.7–24.6)a 12.2 (10.8–13.5)a↓ 5.5 (4.8–6.2) 14.6 (13.1–16.1)a↑ 27.2 (25.7–28.7) 20.0 (18.3–21.7)a↓ 
 Sex       
  Male 24.6 (22.3–26.8)a 15.8 (13.6–18.0)b↓ 4.5 (3.5–5.4)b 11.9 (9.8–13.9)b↑ 31.1 (28.7–33.4)b 24.0 (21.3–26.8)a,b↓ 
  Female 21.9 (20.1–23.7)a 9.1 (7.5–10.7)b↓ 6.4 (5.3–7.4)a,b 16.9 (14.8–19.0)b↑ 23.7 (21.9–25.6)b 16.5 (14.4–18.7)b↓ 
 Race and/or ethnicity       
  Non-Hispanic white 24.8 (23.2–26.5)a,b 14.8 (12.8–16.8)a,b↓ 5.5 (4.7–6.4)a 14.4 (12.4–16.4)a,b↑ 31.2 (29.4–33.1)b 24.3 (21.8–26.7)b↓ 
  Non-Hispanic African American 16.6 (13.4–19.9)ab, 5.9 (3.6–8.2)a,b↓ 6.9 (4.7–9.1) 21.6 (16.9–26.2)a,b↑ 15.0 (11.8–18.2)a,b 13.4 (9.8–17.0)a,b 
  Hispanic 22.1 (16.0–28.2) 11.5 (8.6–14.4)b↓ 5.0 (2.6–7.5) 13.7 (10.5–16.8)b↑ 18.3 (13.7–22.9)b 16.1 (12.2–20.1)b 
  Non-Hispanic other 20.5 (15.0–26.0) 8.3 (5.0–11.6)a,b↓ — 9.7 (6.5–12.9)b↑ 22.8 (17.4–28.1)b 14.9 (10.5–19.3)b↓ 
 Status       
  Full-time 26.6 (22.5–30.6) 10.5 (7.8–13.2)↓ 4.4 (2.9–5.9) 12.7 (9.3–16.0)↑ 26.5 (22.7–30.3) 17.8 (14.1–21.6)↓ 
  Part-time 22.6 (21.0–24.1) 12.6 (11.1–14.1)↓ 5.7 (4.9–6.5) 15.1 (13.4–16.7)↑ 27.3 (25.7–28.9) 20.5 (18.6–22.5)↓ 
       
Noncollege individuals n = 6203 n = 4502 n = 6203 n = 4502 n = 6203 n = 4502 
 Overall 30.7 (29.2–32.1)a 17.4 (16.0–18.9)a ↓ 4.6 (3.9–5.3) 10.8 (9.6–12.0)a↑ 27.1 (25.7–28.4) 23.4 (21.8–25.0)a↓ 
 Sex       
  Male 32.1 (30.0–34.1)a,b 18.3 (16.3–20.3)↓ 4.7 (3.7–5.7) 9.9 (8.3–11.4)↑ 31.1 (29.1–33.1)b 28.1 (25.7–30.4)a,b↓ 
  Female 29.0 (27.1–31.0)a,b 16.3 (14.3–18.3)↓ 4.5 (3.6–5.4)a 12.0 (10.2–13.8)↑ 22.3 (20.5–24.2)b 17.4 (15.4–19.4)b 
 Race and/or ethnicity       
  Non-Hispanic white 34.3 (32.5–36.0)a,b 21.4 (19.3–23.5)a,b↓ 4.1 (3.3–4.9)a,b 9.9 (8.3–11.5)a,b↑ 32.4 (30.6–34.1)b 27.0 (24.7–29.3)b↓ 
  Non-Hispanic African American 22.8 (19.5–26.0)a,b 11.9 (9.2–14.6)a,b↓ 7.6 (5.7–9.6)b 14.3 (11.4–17.3)a,b↑ 21.1 (17.9–24.3)a,b 19.4 (16.0–22.8)a,b 
  Hispanic 27.4 (23.9–30.9)b 13.0 (10.2–15.8)b↓ 4.0 (2.2–5.8)b 11.3 (8.7–13.9)b↑ 17.5 (14.6–20.4)b 17.9 (14.6–21.2)b↑ 
  Non-Hispanic other 27.4 (20.8–34.0)b 13.8 (9.5–18.2)a,b↓ 4.8 (2.0–7.7)b 8.4 (5.2–11.6)b↑ 27.5 (20.6–34.5)b 21.8 (16.4–27.3)b 
 Education       
  Less than high school 30.8 (28.5–33.0) 15.7 (13.4–18.0)b↓ 3.7 (2.7–4.6)b 10.9 (8.8–13.1)↑ 27.6 (25.5–29.8) 19.9 (17.2–22.6)b↓ 
  High school 30.3 (28.2–32.5) 20.1 (17.7–22.4)b↓ 5.4 (4.2–6.7)b 9.8 (8.1–11.6)↑ 26.0 (23.9–28.1) 25.0 (22.4–27.6)b 
  Some college or higher 31.3 (27.9–34.7) 15.4 (12.7–18.1)b↓ 5.2 (3.6–6.9)b 12.1 (9.7–14.4)↑ 28.2 (24.7–31.7) 24.8 (21.6–28.0)b 

Data are presented as % (95% CI). ↑ indicates prevalence linearly increased during 2002–2016 (P < .05), and ↓ indicates prevalence linearly decreased during 2002–2016 (P < .05). Exclusive use of smoked tobacco was defined as use of cigarettes and/or cigars (big cigars, cigarillos, and/or little cigars) without using marijuana. Exclusive use of marijuana was defined as use of marijuana (regardless of the mode of consumption) without using smoked tobacco. CI, confidence interval; —, estimates suppressed because of relative SE ≥30%.

a

Results significantly differ from corresponding estimate among college and noncollege young adults (P < .05).

b

Responses vary significantly (P < .05) within the assessed demographic subgroups.

FIGURE 1

Trends in the prevalence of past-12-month exclusive smoked tobacco use, marijuana use, and dual use among college and noncollege young adults aged 18 to 22 years (NSDUH, United States, 2002–2016). Exclusive use of smoked tobacco was defined as use of cigarettes and/or cigars (big cigars, cigarillos, and/or little cigars) without using marijuana. Exclusive use of marijuana was defined as use of marijuana (regardless of the mode of consumption) without using smoked tobacco.

FIGURE 1

Trends in the prevalence of past-12-month exclusive smoked tobacco use, marijuana use, and dual use among college and noncollege young adults aged 18 to 22 years (NSDUH, United States, 2002–2016). Exclusive use of smoked tobacco was defined as use of cigarettes and/or cigars (big cigars, cigarillos, and/or little cigars) without using marijuana. Exclusive use of marijuana was defined as use of marijuana (regardless of the mode of consumption) without using smoked tobacco.

Among noncollege young adults during 2002 to 2016, exclusive tobacco smoking declined from 33.6% to 17.7% (RPC = −47.3) for past-30-day use and from 30.7% to 17.4% (RPC = −43.2) for past-12-month use (Tables 3 and 4, Fig 1, Supplemental Fig 2). Declines were significant within all noncollege population subgroups. During 2016, exclusive tobacco smoking prevalence was highest among non-Hispanic whites for both past-30-day (21.8%) and past-12-month (21.4%) usage. By education, prevalence was highest among high school graduates for past-30-day (21.3%) and past-12-month (20.1%) use. In 2016, compared with college students, noncollege young adults had a significantly higher prevalence of exclusive tobacco smoking for both past-30-day (17.7% vs 10.4%) and past-12-month (17.4% vs 12.2%) use (all P < .05).

Among college students, exclusive marijuana use increased during 2002 to 2016 from 3.6% to 11.5% (RPC = 219.7) for past-30-day use and 5.5% to 14.6% (RPC = 166.6) for past-12-month use (Tables 3 and 4, Fig 1, Supplemental Fig 2). Increases were significant within all population subgroups assessed. During 2016, past-30-day exclusive marijuana use did not differ by demographics, whereas past-12-month use was significantly higher among females than among males (16.9% vs 11.9%) and among non-Hispanic African Americans (21.6%) than among all other racial and/or ethnic groups (all P < .05).

Among noncollege young adults during 2002 to 2016, exclusive marijuana use increased from 3.2% to 8.6% (RPC = 167.2) for past-30-day use and from 4.6% to 10.8% (RPC = 133.7) for past-12-month use (Tables 3 and 4, Fig 1, Supplemental Fig 2). Increases were significant within all subgroups assessed. During 2016, past-30-day exclusive marijuana use did not differ by demographics, whereas past-12-month use was highest among non-Hispanic African Americans (14.3%). Compared with college students during 2016, exclusive marijuana use was significantly lower among noncollege young adults both for past-30-day (8.6% vs 11.5%) and past-12-month (10.8% vs 14.6%) use (all P < .05).

Among college students, dual use decreased during 2002 to 2016, from 14.4% to 8.7% (RPC = −39.4) for past-30-day use and from 27.2% to 20.0% (RPC = −26.4) for past-12-month use. Declines were significant among all population subgroups assessed except non-Hispanic African Americans and Hispanics (Tables 3 and 4). In 2016, prevalence was significantly higher among males than females for both past-30-day (11.6% vs 6.3%) and past-12-month (24.0% vs 16.5%) use. By race and/or ethnicity, prevalence was highest among white college students for both past-30-day (11.0%) and past-12-month (24.3%) use (all P < .05).

Among noncollege young adults, dual use decreased during 2002 to 2016, from 15.7% to 13.0% (RPC = −16.9) for past-30-day use and from 27.1% to 23.4% (RPC = −13.6) for past-12-month use (Tables 3 and 4, Fig 1, Supplemental Fig 2). Within subgroup analyses, declines were significant among males and non-Hispanic whites (for both past-30-day and past-12-month use) and those with less than a high school education (for past-12-month use); in contrast, prevalence increased among Hispanics (for both past-30-day and past-12-month use). During 2016, the prevalence of dual use was higher among males than among females for both past-30-day (15.8% vs 9.4%) and past-12-month use (28.1% vs 17.4%). By race and/or ethnicity, prevalence was highest among whites for both past-30-day (14.9%) and past-12-month use (27.0%). By education, prevalence was highest among high school graduates for past-12-month use (25.0%). Compared with college students during 2016, noncollege young adults had a significantly higher prevalence of dual use for both past-30-day (13.0% vs 8.7%) and past-12-month (23.4% vs 20.0%) use.

Among all college-aged young adults during 2002 to 2016, exclusive use of marijuana increased, whereas exclusive use of smoked tobacco products decreased, and rates of these changes were greater among college students. The contrasting trends in tobacco versus marijuana could reflect differences in risk perception and social norms regarding the use of these products. Specifically, the recent increase in legalization of marijuana in various states across the country could be an indication of changing social norms toward marijuana use.23,28,29 

Our findings revealed different behavioral patterns between college students and noncollege individuals. During 2016, whereas the prevalence of overall marijuana use was not significantly different between college students and noncollege young adults for both past-30-day and past-12-month usage, a larger segment of noncollege marijuana users concurrently engaged in smoking tobacco. During 2002, however, the prevalence of dual use did not vary between college students and noncollege individuals. Furthermore, among noncollege young adults during 2002 to 2016, the prevalence of past-12-month exclusive tobacco smoking was lower than that of past-30-day exclusive tobacco smoking, suggesting that many individuals who recently smoked tobacco had engaged in concurrent use of marijuana earlier in the year. Tobacco products are still widely available for college-aged young adults, and marijuana sale continues to evolve across states. Given this landscape, our findings reinforce the importance of continued surveillance of the use, perceptions, and social acceptability of these products to understand usage behaviors among college-aged adults overall and in demographic subgroups coupled with research on the health effects of dual use of these products.

Use of marijuana in the past 12 months, but not in the past 30 days, could suggest experimental or occasional use rather than frequent use. Comparison of past-30-day and past-12-month prevalence estimates in this study indicate a high prevalence of such intermittent marijuana use for certain population subgroups. For example, in 2016, although no significant differences existed by race and/or ethnicity in past-30-day exclusive use of marijuana, significant differences were found for past-12-month exclusive marijuana use. The largest differences were noted for non-Hispanic African Americans, both among college students (9.8% vs 17.8% [past 30 days versus past 12 months]) and noncollege young adults (10.7% vs 14.3% [past 30 days versus past 12 months]). This pattern was not observed for exclusive smoked tobacco use. In light of these findings, further studies could be beneficial to better understand intermittent marijuana use behavior among college-aged young adults. The relatively high prevalence of intermittent marijuana use also reinforces the importance of continued surveillance of not only recent usage behaviors of marijuana and tobacco but also those extending over longer periods.

Issues of college-aged young adults are of importance for youth. Pediatric practitioners can play a key role in addressing some of the social underpinnings of marijuana use and tobacco smoking among young people, including addressing youth substance use behaviors during their visits. Furthermore, given that college-aged young adults are a reproductive population, the implications of use of or exposure to tobacco and marijuana smoke can extend beyond the immediate harms to the smoker and may also impact pregnancy outcomes.30,31  When counseling youth, pediatric practitioners can reinforce this point for preparing youth for life as early adults.

Strengths of this study include the use of nationally representative data over a continuous 15-year period to assess trends in marijuana and tobacco use behaviors among college students. The use of a comparison group (noncollege young adults) further strengthens the validity of the findings. Nonetheless, the findings in this study are subject to at least 4 limitations. First, data were self-reported, which might have resulted in recall and social desirability biases. Specifically, we were unable to examine whether decriminalization and legalization of adult marijuana use affected self-reporting bias; that is, respondents might have felt more comfortable reporting marijuana use as it became legal in more states. Second, the definition of tobacco smoking in this study did not include all forms of tobacco products available in the United States because cigarettes and cigars were the only products for which both past-30-day and past-12-month use were assessed. Third, the survey did not assess the mode by which marijuana was consumed (eg, smoking, vaping, or eating), which prevented nuanced analyses of marijuana consumption patterns and their relationships with tobacco use. Finally, because the survey does not include institutionalized populations and persons in the military in its sample, the results might not be generalizable to those populations.

Continued surveillance of tobacco and marijuana use will be important to monitor the impact that legal adult use of marijuana has on usage patterns among young people in the United States.

Ms Odani conceptualized and designed the study, conducted data analyses, and drafted the initial manuscript with Dr Soura; Drs Soura and King, Mr Tynan, and Ms Lavinghouze helped conceptualize the study and critically reviewed and revised the manuscript; Dr Agaku conceptualized and designed the study and critically reviewed and revised the manuscript; and all authors approve the final manuscript as submitted and agree to be accountable for all aspects of the work.

The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the US Centers for Disease Control and Prevention.

FUNDING: No external funding.

COMPANION PAPER: A companion to this article can be found online at www.pediatrics.org/cgi/doi/10.1542/peds.2019-3025.

     
  • RPC

    relative percentage change

  •  
  • NSDUH

    National Survey on Drug Use and Health

1
ProCon.org
.
Legal recreational marijuana states and DC. 2018. Available at: https://marijuana.procon.org/view.resource.php?resourceID=006868. Accessed March 14, 2019
2
Ramo
DE
,
Liu
H
,
Prochaska
JJ
.
Tobacco and marijuana use among adolescents and young adults: a systematic review of their co-use
.
Clin Psychol Rev
.
2012
;
32
(
2
):
105
121
3
Cohn
A
,
Johnson
A
,
Ehlke
S
,
Villanti
AC
.
Characterizing substance use and mental health profiles of cigar, blunt, and non-blunt marijuana users from the National Survey of Drug Use and Health
.
Drug Alcohol Depend
.
2016
;
160
:
105
111
4
Leafly
.
What’s the difference between joints, blunts, and spliffs? 2015. Available at: https://www.leafly.com/news/cannabis-101/whats-the-difference-between-joints-blunts-and-spliffs. Accessed March 14, 2019
5
Schauer
GL
,
Berg
CJ
,
Kegler
MC
,
Donovan
DM
,
Windle
M
.
Assessing the overlap between tobacco and marijuana: trends in patterns of co-use of tobacco and marijuana in adults from 2003-2012
.
Addict Behav
.
2015
;
49
:
26
32
6
Schauer
GL
,
Berg
CJ
,
Kegler
MC
,
Donovan
DM
,
Windle
M
.
Differences in tobacco product use among past month adult marijuana users and nonusers: findings from the 2003-2012 national survey on drug use and health
.
Nicotine Tob Res
.
2016
;
18
(
3
):
281
288
7
Giroud
C
,
de Cesare
M
,
Berthet
A
, et al
.
E-cigarettes: a review of new trends in cannabis use
.
Int J Environ Res Public Health
.
2015
;
12
(
8
):
9988
10008
8
Beenstock
M
,
Rahav
G
.
Testing Gateway Theory: do cigarette prices affect illicit drug use?
J Health Econ
.
2002
;
21
(
4
):
679
698
9
Bentler
P
,
Newcomb
M
,
Zimmerman
M
. Cigarette Use and Drug Use Progression: Growth Trajectory and Lagged Effect Hypotheses. In:
Kandel
DB
, ed.
Stages and Pathways of Drug Involvement Examining the Gateway Hypothesis
.
Cambridge, United Kingdom
:
Cambridge University Press
;
2002
:
223
253
10
Hindocha
C
,
Shaban
ND
,
Freeman
TP
, et al
.
Associations between cigarette smoking and cannabis dependence: a longitudinal study of young cannabis users in the United Kingdom
.
Drug Alcohol Depend
.
2015
;
148
:
165
171
11
Timberlake
DS
,
Haberstick
BC
,
Hopfer
CJ
, et al
.
Progression from marijuana use to daily smoking and nicotine dependence in a national sample of U.S. adolescents
.
Drug Alcohol Depend
.
2007
;
88
(
2–3
):
272
281
12
Agrawal
A
,
Madden
PA
,
Bucholz
KK
,
Heath
AC
,
Lynskey
MT
.
Transitions to regular smoking and to nicotine dependence in women using cannabis
.
Drug Alcohol Depend
.
2008
;
95
(
1–2
):
107
114
13
Behrendt
S
,
Wittchen
HU
,
Höfler
M
,
Lieb
R
,
Beesdo
K
.
Transitions from first substance use to substance use disorders in adolescence: is early onset associated with a rapid escalation?
Drug Alcohol Depend
.
2009
;
99
(
1–3
):
68
78
14
National Academies of Sciences, Engineering, and Medicine
;
Health and Medicine Division
;
Board on Population Health and Public Health Practice
;
Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda
. The National Academies Collection: Reports Funded by National Institutes of Health. In:
The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research
.
Washington, DC
:
National Academies Press (US)
;
2017
15
World Health Organization
.
The health and social effects of nonmedical cannabis use.
2015
. Available at: https://www.who.int/substance_abuse/publications/msbcannabis.pdf. Accessed March 14, 2019
16
Schauer
GL
,
King
BA
,
Bunnell
RE
,
Promoff
G
,
McAfee
TA
.
Toking, vaping, and eating for health or fun: marijuana use patterns in adults, US, 2014
.
Am J Prev Med
.
2016
;
50
(
1
):
1
8
17
Moir
D
,
Rickert
WS
,
Levasseur
G
, et al
.
A comparison of mainstream and sidestream marijuana and tobacco cigarette smoke produced under two machine smoking conditions
.
Chem Res Toxicol
.
2008
;
21
(
2
):
494
502
18
Fairman
BJ
,
Furr-Holden
CD
,
Johnson
RM
.
When marijuana is used before cigarettes or alcohol: demographic predictors and associations with heavy use, cannabis use disorder, and other drug-related outcomes [published correction appears in Prev Sci. 2019;20(2):234]
.
Prev Sci
.
2019
;
20
(
2
):
225
233
19
Kandel
D
,
Kandel
E
.
The Gateway Hypothesis of substance abuse: developmental, biological and societal perspectives
.
Acta Paediatr
.
2015
;
104
(
2
):
130
137
20
Brook
JS
,
Lee
JY
,
Brook
DW
.
Trajectories of marijuana use beginning in adolescence predict tobacco dependence in adulthood
.
Subst Abus
.
2015
;
36
(
4
):
470
477
21
Windle
M
,
Haardörfer
R
,
Lloyd
SA
,
Foster
B
,
Berg
CJ
.
Social influences on college student use of tobacco products, alcohol, and marijuana
.
Subst Use Misuse
.
2017
;
52
(
9
):
1111
1119
22
Schulenberg
JE
,
Johnston
LD
,
O’Malley
PM
, et al
.
Monitoring the Future National Survey Results on Drug Use, 1975–2016: Volume II, College Students and Adults Ages 19–55
.
Ann Arbor, MI
:
Institute for Social Research. University of Michigan
;
2017
23
Miech
RA
,
Patrick
ME
,
O’Malley
PM
,
Johnston
LD
.
The influence of college attendance on risk for marijuana initiation in the United States: 1977 to 2015
.
Am J Public Health
.
2017
;
107
(
6
):
996
1002
24
Ramo
DE
,
Delucchi
KL
,
Hall
SM
,
Liu
H
,
Prochaska
JJ
.
Marijuana and tobacco co-use in young adults: patterns and thoughts about use
.
J Stud Alcohol Drugs
.
2013
;
74
(
2
):
301
310
25
Montgomery
L
.
Marijuana and tobacco use and co-use among African Americans: results from the 2013 National Survey on Drug Use and Health
.
Addict Behav
.
2015
;
51
:
18
23
26
Centers for Disease Control and Prevention
.
National Adult Tobacco Survey (NATS). 2018. Available at: https://www.cdc.gov/tobacco/data_statistics/surveys/nats/index.htm. Accessed March 14, 2019
27
Meier
E
,
Hatsukami
DK
.
A review of the additive health risk of cannabis and tobacco co-use
.
Drug Alcohol Depend
.
2016
;
166
:
6
12
28
Maloff
D
.
A review of the effects of the decriminalization of marijuana
.
Contemp Drug Probl
.
1981
;
10
:
307
29
Pew Research Center
.
About six-in-ten Americans support marijuana legalization. 2018. Available at: www.pewresearch.org/fact-tank/2018/10/08/americans-support-marijuana-legalization/. Accessed March 14, 2019
30
Centers for Disease Control and Prevention
.
Smoking during pregnancy. 2018. Available at: https://www.cdc.gov/tobacco/basic_information/health_effects/pregnancy/index.htm. Accessed March 14, 2019
31
Centers for Disease Control and Prevention
.
What you need to know about marijuana and pregnancy. 2018. Available at: https://www.cdc.gov/marijuana/factsheets/pregnancy.htm. Accessed March 14, 2019

Competing Interests

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.

FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.

Supplementary data