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| MMWR Surveillance Summaries Vol. 65, No. SS-11 September 2, 2016 |
National Estimates of Marijuana Use and Related Indicators — National Survey on Drug Use and Health, United States, 2002–2014
Surveillance Summaries / September 2, 2016 / 65(11);1–25
Alejandro Azofeifa, DDS1; Margaret E. Mattson, PhD1; Gillian Schauer, PhD2; Tim McAfee, MD3;
View suggested citationAbstract
Problem/Condition: In the United States, marijuana is the most commonly used illicit drug. In 2013, 7.5% (19.8 million) of the U.S. population aged ≥12 years reported using marijuana during the preceding month. Because of certain state-level policies that have legalized marijuana for medical or recreational use, population-based data on marijuana use and other related indicators are needed to help monitor behavioral health changes in the United States.
Period Covered: 2002–2014.
Description of System: The National Survey on Drug Use and Health (NSDUH) is a national- and state-level survey of a representative sample of the civilian, noninstitutionalized U.S. population aged ≥12 years. NSDUH collects information about the use of illicit drugs, alcohol, and tobacco; initiation of substance use; frequency of substance use; substance dependence and abuse; perception of substance harm risk or no risk; and other related behavioral health indicators. This report describes national trends for selected marijuana use and related indicators, including prevalence of marijuana use; initiation; perception of harm risk, approval, and attitudes; perception of availability and mode of acquisition; dependence and abuse; and perception of legal penalty for marijuana possession.
Results: In 2014, a total of 2.5 million persons aged ≥12 years had used marijuana for the first time during the preceding 12 months, an average of approximately 7,000 new users each day. During 2002–2014, the prevalence of marijuana use during the past month, past year, and daily or almost daily increased among persons aged ≥18 years, but not among those aged 12–17 years. Among persons aged ≥12 years, the prevalence of perceived great risk from smoking marijuana once or twice a week and once a month decreased and the prevalence of perceived no risk increased. The prevalence of past year marijuana dependence and abuse decreased, except among persons aged ≥26 years. Among persons aged ≥12 years, the percentage reporting that marijuana was fairly easy or very easy to obtain increased. The percentage of persons aged ≥12 reporting the mode of acquisition of marijuana was buying it and growing it increased versus getting it for free and sharing it. The percentage of persons aged ≥12 years reporting that the perceived maximum legal penalty for the possession of an ounce or less of marijuana in their state is a fine and no penalty increased versus probation, community service, possible prison sentence, and mandatory prison sentence.
Interpretation: Since 2002, marijuana use in the United States has increased among persons aged ≥18 years, but not among those aged 12–17 years. A decrease in the perception of great risk from smoking marijuana combined with increases in the perception of availability (i.e., fairly easy or very easy to obtain marijuana) and fewer punitive legal penalties (e.g., no penalty) for the possession of marijuana for personal use might play a role in increased use among adults.
Public Health Action: National- and state-level data can help federal, state, and local public health officials develop targeted prevention activities to reduce youth initiation of marijuana use, prevent marijuana dependence and abuse, and prevent adverse health effects. As state-level laws on medical and recreational marijuana use change, modifications might be needed to national- and state-level surveys and more timely and comprehensive surveillance systems might be necessary to provide these data. Marijuana use in younger age groups is a particular public health concern, and changing the perception of harm risk from smoking marijuana is needed.
Introduction
In the United States, marijuana (cannabis) is the most commonly used illicit drug (1). In 2013, data from the National Survey on Drug Use and Health (NSDUH) indicated that approximately 2.4 million persons aged ≥12 years had used marijuana for the first time during the preceding 12 months, an average of approximately 6,600 new users each day (1). Among persons aged ≥12 years, approximately 8.1 million had used marijuana on 20 or more days during the preceding month (1), and approximately 4.2 million met the criteria for marijuana dependence and abuse* during the preceding year (1). Increased trends in substance use can coincide with decreased trends in perceived risk (1). According to NSDUH data, the prevalence of past month marijuana use among persons aged 12–17 years increased from 6.7% in 2006 to 7.1% in 2013, and the percentage who perceived great risk from smoking marijuana once a month decreased from 34.6% in 2006 to 24.2% in 2013 (1).
The health effects associated with marijuana use are widely debated. However, regular use (i.e., daily or almost daily use) of marijuana or use during adolescence poses potential public health concerns, including reduced educational attainment, potential long-term health consequences, addiction in some users, increased risk for psychoses disorders, altered brain structure and function, and increased risk for injury from driving while under the influence (2–8).
Since 1971, NSDUH has been the principal national source of statistical information on the use of illicit drugs, alcohol, and tobacco. Several national- and state-level reports on substance use have been published by the Substance Abuse and Mental Health Services Administration (SAMHSA) using NSDUH data (9). To date, no comprehensive national report has focused only on a specific substance (e.g., marijuana). This report is the first to present an overview of national estimates for marijuana use and related indicators for the U.S. civilian noninstitutionalized population aged ≥12 years using 2002–2014 NSDUH data. Findings from this report can provide federal, state, and local public health officials with information about behavioral trends for marijuana use and related indicators. Public health officials can use these findings to develop and implement targeted prevention activities to reduce youth initiation and use of marijuana. Findings can also be used to assess the quality, relevance, and timeliness of surveillance capacity to effectively monitor trends of marijuana use.
Methods
Data Source and Collection
NSDUH collects information about the use of illicit drugs, alcohol, and tobacco among the U.S. noninstitutionalized civilian population aged ≥12 years (10). NSDUH respondents include residents of households and noninstitutional group quarters (e.g., shelters, rooming houses, dormitories, migratory workers’ camps, and halfway houses) and civilians living on military bases. Homeless persons who do not use shelters, active duty military personnel, and residents of institutional group quarters (e.g., correctional facilities, nursing homes, mental institutions, and long-term hospitals) are excluded. NSDUH data are collected annually via household face-to-face interviews using computer-assisted personal interviewing methods. An independent, multistage area probability sample design for each of the 50 states and the District of Columbia allows for the production of state-level estimates. NSDUH oversamples youth (aged 12–17 years) and young adults (aged 18–25 years) to allow increased precision in those age groups. Additional information about sample design can be found elsewhere (11,12).
NSDUH is planned and managed by the Center for Behavioral Health Statistics and Quality (CBHSQ) at SAMHSA. Data are collected and processed by RTI International (Research Triangle Park, North Carolina) through a contract with CBHSQ. The data presented in this report are limited to the years 2002–2014 using NSDUH’s restricted files. Data are protected under the Confidential Information Protection and Statistical Efficiency Act of 2002 (PL 107-347), which ensures that all NSDUH data are used for statistical purposes only and cannot be used for any other purposes. NSDUH was reviewed and approved by RTI International’s Institutional Review Board (protocol ID no. 13961, project no. 0213986). NSDUH is authorized by Section 505 of the Public Health Service Act (available at https://www.gpo.gov/fdsys/pkg/USCODE-2010-title42/pdf/USCODE-2010-title42-chap6A-subchapIII-partA-sec282.pdf). More information about confidentiality and Office of Management and Budget approval is available at http://www.reginfo.gov/public/do/PRAViewICR?ref_nbr=200106-0930-004. Changes to the NSDUH survey design and methodology occurred in 1999 and 2002; therefore, survey data collected before 2002 are not comparable to those collected during 2002–2014. These changes included a transition from paper-and-pencil interviewing to computer-assisted interviewing, improvements to data collection quality control procedures, and the addition of a $30 monetary incentive. During 2002–2014, the only change implemented involved the use of census data to produce the sample weights. In 2002, the 2000 decennial census data were introduced and used in the 2002–2010 sample weights and in 2011, the 2010 census data were introduced and used in the 2011–2014 sample weights. However, those weight changes were not substantial enough to cause a break in comparability with earlier years. Detailed information regarding the NSDUH methodology and questionnaire is available elsewhere (9–12).
Sample Design
During 2002–2013, states with the largest population were designated as large sample states (California, Florida, Illinois, Michigan, New York, Ohio, Pennsylvania, and Texas); these eight states had an annual target sample size of 3,600 participants per state. The remaining 42 states and the District of Columbia had an annual target sample size of 900 participants per state. Beginning in 2014, the sample was redesigned from a two-state sample size group (i.e., 3,600 and 900) to a six-state sample size group (i.e., 4,560, 3,300, 2,400, 1,500, 967, and 960) along with a change in the age-group allocation. This redesign means that the sample allocation is more proportional to the population size in each state (compared with the 2002–2013 sample design), which will result in generally increased precision of national estimates among various age groups (11,12). Additional details about the NSDUH 2014 redesign are available elsewhere (12).
Questionnaire
Marijuana use was defined in NSDUH as a self-report of using marijuana (pot or grass) or hashish (hash). All questions about marijuana in NSDUH were screened by answering positively to the following question: “Have you ever, even once, used marijuana or hashish?” For this report, national estimates were developed from six related indicators of marijuana use patterns and perceptions: 1) marijuana use; 2) marijuana initiation; 3) perception of harm risk, approval, and attitudes; 4) perception of availability and mode of acquisition; 5) marijuana dependence and abuse; and 6) marijuana possession–criminal justice (Box). The detailed NSDUH questionnaire is available at http://www.samhsa.gov/data/population-data-nsduh/reports?tab=39.
Variables
NSDUH data on marijuana use during the preceding month include the following demographic characteristics: age, sex, race/ethnicity, highest level of education completed, current employment status, and geographic area of residence (i.e., census region). Age was categorized into four groups: total (≥12 years), 12–17 years, 18–25 years, and ≥26 years. Sex was categorized into males and females. Race/ethnicity was categorized into seven groups: non-Hispanic white, non-Hispanic black or African America, non-Hispanic American Indian/Alaska Native, non-Hispanic Hawaiian/Other Pacific Islander, non-Hispanic Asian, non-Hispanic two or more races,† and Hispanic or Latino. Highest level of education completed was categorized into four groups: less than high school, high school, some college, and college graduate. Current employment status was categorized into four groups: full-time employment, part-time employment, unemployed, and other (e.g., student, keeping house or caring for children full-time, retired, or disabled). Geographic area of residence was divided into four regions (Northeast, South, Midwest, and West) as defined by the Census Bureau.§ This report presents national estimates of marijuana use and related indicators for all persons aged ≥12 years and three age subgroups (12–17 years, 18–25 years, and ≥26 years).
Analysis
Statistical analyses were performed using SUDAAN version 11.0.1 (RTI International, Research Triangle Park, North Carolina). Prevalence measures, 95% confidence intervals, linear p-values, and relative prevalence differences for marijuana use and related indicators are presented in this report. Population weights were calibrated through a model-based procedure to state, age group, sex, and race/ethnicity groupings, and variances were calculated accounting for the complex survey design. Thirteen years (2002–2014) of sample survey weights were used to produce national population estimates. Logistic regression analysis was used to examine linear temporal trends during 2002–2014. Each dichotomous indicator (e.g., marijuana use status: yes/no for each group) was separately regressed on year of survey to determine whether year could be a predictor of the likelihood of persons using marijuana over time. A level of α≤0.05 was used to determine the statistical significance of the trends. The relative prevalence difference (diff) was calculated between the 2002 and 2014 national estimates, as an overall measure of the relative change in marijuana use or other related indicator over the period. A plus sign (+) indicates an increase in prevalence, a minus sign (-) indicates a decrease in prevalence, and no sign indicates no difference. National estimates presented in the report have met the criteria for statistical reliability. The criteria used to define unreliability of direct estimates from NSDUH are determined on the basis of the prevalence (proportion estimates), relative standard error (RSE, defined as the ratio of the standard error over the estimate), and sample size for each estimate. Estimates not meeting these criteria were suppressed and not included in the tables or figures, and suppressed estimates were not included in the statistical test analysis. Prevalence estimates were suppressed if any of the following occurred: 1) the prevalence estimate was <0.005% or >99.995%; 2) the RSE of the negative natural logarithm of the estimated proportion p (where p is the prevalence divided by 100) was >0.175 if the prevalence is ≤50%; 3) the RSE of the negative of the natural logarithm of (1-p) is >0.175 if the prevalence is >50%; 4) the actual sample size is <100; or 5) the effective sample size (defined as the sample size divided by the design effect) is <68. Additional information about NSDUH and its statistical methods and definitions is available elsewhere (9–11). Detailed national and state-level estimates on marijuana use and related indicators are available at http://www.samhsa.gov/atod/marijuana.
Results
Sample Size, Response Rates, and Population Estimates
During 2002–2014, NSDUH data were collected from 884,742 completed individual respondent interviews (68,057 annual average). Annual average weighted response rates for interviews were 74.8%, for an estimated total of 250,065,195 persons of the U.S. population during the 2002–2014 period. Person-level weights were determined on the basis of probabilities of selection, nonresponse adjustments, and poststratification to population estimates obtained from the Census Bureau. Table 1 displays the survey year distributions of sample size, weighted interview rates, and population estimates in NSDUH during 2002–2014.
Marijuana Use
Past Month Use
In 2014, the estimated national prevalence of past month marijuana use among persons aged ≥12 years was 8.4%. From 2002 to 2014, the prevalence of past month marijuana use increased by 35.0% (from 6.2% in 2002 to 8.4% in 2014; p<0.001) among persons aged ≥12 years. The prevalence of past month marijuana use increased among persons aged ≥18 years; the increase was greatest among adults aged ≥55 years (Table 2). In general, the prevalence of past month marijuana use increased across the majority of selected demographic characteristics (i.e., sex, race/ethnicity, highest level of education completed, current employment status, and U.S. geographic region) (Figures 1, 2, 3, 4, and 5).
Past Year Use
In 2014, the estimated national prevalence of past year marijuana use among persons aged ≥12 years was 13.2%. From 2002 to 2014, the prevalence of marijuana use in the past year increased by 20.0% (from 11.0% in 2002 to 13.2% in 2014; p<0.001) among persons aged ≥12 years. The prevalence of past year marijuana use decreased by 17.0% (from 15.8% in 2002 to 13.1% in 2014; p<0.001) among persons aged 12–17 years. In contrast, the prevalence of past year marijuana use increased by 7.0% among persons aged 18–25 years (from 29.8% in 2002 to 31.9% in 2014; p<0.001) and by 44.0% among those aged ≥26 years (from 7.0% in 2002 to 10.1% in 2014; p<0.001) (Table 3).
Daily or Almost Daily Use
In 2014, the estimated national prevalence of daily or almost daily use of marijuana in the past year and in the past month among persons aged ≥12 years was 2.5% and 3.5%, respectively. From 2002 to 2014, the prevalence of daily or almost daily marijuana use in the past year increased by 92.0% (from 1.3% in 2002 to 2.5% in 2014; p<0.001) and in the past month increased by 75.0% (from 2.0% in 2002 to 3.5% in 2014; p<0.001) among persons aged ≥12 years. Stratifying the data by age, an increase in past year and past month daily or almost daily use occurred among almost all persons aged ≥18 years, but a decrease occurred among persons aged 12–17 years (Table 4). These trends were the same when restricting the analyses to only past year or past month marijuana users for the reporting period (Table 5).
Marijuana Initiation
Initiation and Mean Age
In 2014, the estimated national prevalence of past year initiation among persons at risk (i.e., those who did not use marijuana in their lifetime or who used marijuana for the first time during the preceding 12 months) among persons aged ≥12 years was 1.7%. From 2002 to 2014, the prevalence of past year initiation among persons at risk increased by 13.0% (from 1.5% in 2002 to 1.7% in 2014; p<0.001) among persons aged ≥12 years (range: 2.1 million new users in 2002 to 2.5 million new users in 2014); in 2014, this averaged to about 7,000 new users each day (approximately 1,000 more new users each day compared with 2002). Furthermore, the prevalence of past year initiation increased by 27.0% (from 4.9% in 2002 to 6.2% in 2014; p<0.001) among persons at risk aged 18–25 years. Overall, the mean age at first use had increased for all age groups during 2002–2014. In 2014, the mean age at first use estimate among persons aged ≥12 years was <19 years; among persons aged 12–17 years, the estimated mean age at first use of marijuana among past year initiates was <15 years (Table 6).
Perception of Harm Risk, Approval, and Attitudes
Perceived Great Risk and No Risk from Smoking Marijuana Once a Month
In 2014, the estimated national prevalence of perceived great risk from smoking marijuana once a month among persons aged ≥12 years was 26.5%. From 2002 to 2014, the prevalence of perceived great risk from smoking marijuana once a month decreased by 31.0% (from 38.3% in 2002 to 26.5% in 2014; p<0.001) among persons aged ≥12 years. A linear decrease in the prevalence of perceived great risk from smoking marijuana once a month was also observed in all age groups. Conversely, during 2002–2014 the percentage of persons perceiving no risk from smoking marijuana once a month increased in all age groups (Table 7).
Perceived Great Risk and No Risk from Smoking Marijuana Once or Twice a Week
In 2014, the estimated national prevalence of perceived great risk from smoking marijuana once or twice a week among persons aged ≥12 years was 34.3%. From 2002 to 2014, the prevalence of perceived great risk from smoking marijuana once or twice a week decreased by 33.0% (from 51.3% in 2002 to 34.3% in 2014; p<0.001) among persons aged ≥12 years. A linear decrease in the prevalence of perceived great risk from smoking marijuana once or twice a week was also observed in all age groups. Conversely, during 2002–2014 the percentage of persons perceiving no risk from smoking marijuana once or twice a week increased in all age groups (Table 7).
Perceived Parental Disapproval of Trying Marijuana Once or Twice and Using Marijuana Once a Month or More
In 2014, the estimated national prevalence of perceived parental disapproval of trying marijuana once or twice among all persons aged 12–17 and past month marijuana users aged 12–17 years was 95.4% and 78.5%, respectively. From 2002 to 2014, the prevalence of perceived parental disapproval of trying marijuana once or twice decreased by 6.0% (from 83.8% in 2002 to 78.5% in 2014; p<0.001) only among past month marijuana users aged 12–17 years (Figure 6). No change was observed among all persons aged 12–17 years.
In 2014, the estimated national prevalence of perceived parental disapproval of using marijuana once a month or more among all persons aged 12–17 years and past month marijuana users aged 12–17 years was 95.7% and 78.8%, respectively. From 2002 to 2014, the prevalence of perceived parental disapproval of using marijuana once a month or more decreased by 1.0% among all persons aged 12–17 years (from 96.3% in 2002 to 95.7% in 2014; p<0.001) and by 8.0% (from 85.7% in 2002 to 78.8% in 2014; p<0.001) among past month marijuana users aged 12–17 years (Figure 7).
Attitudes Toward Peers Trying Marijuana Once or Twice and Using Marijuana Once a Month or More
In 2014, the estimated national prevalence of disapproving attitudes toward peers trying marijuana once or twice among all persons aged 12–17 years and past month marijuana users aged 12–17 years was 79.5% and 25.3%, respectively. From 2002 to 2014, the prevalence of disapproving attitudes toward peers trying marijuana once a month or more decreased by 16.0% (from 30.2% in 2002 to 25.3% in 2014; p<0.001) only among past month marijuana users aged 12–17 years. No change was observed among all persons aged 12–17 years (Figure 8).
In 2014, the estimated national prevalence of disapproving attitudes toward peers using marijuana once a month or more among all persons aged 12–17 years and past month marijuana users aged 12–17 years was 79.2% and 21.7%, respectively. From 2002 to 2014, the prevalence of disapproving attitudes toward peers using marijuana once a month or more decreased by 1.0% (from 80.4% in 2002 to 79.2% in 2014; p<0.001) among all persons aged 12–17 years. The prevalence of disapproving attitudes toward peers using marijuana once a month or more decreased by 23.0% (from 28.1% in 2002 to 21.7% in 2014; p<0.001) among past month marijuana users aged 12–17 years (Figure 9).
Perception of Availability and Mode of Acquisition of Marijuana
Perceived Availability
In 2014, the estimated national prevalence of perceived availability (i.e., that it would be fairly easy or very easy to obtain marijuana) among persons aged ≥12 years was 60.2%. From 2002 to 2014, the perceived availability increased by 4.0% (from 58.0% in 2002 to 60.2% in 2014; p<0.05) among persons aged ≥12 years. In contrast, the perceived availability decreased by 13.0% among persons aged 12–17 years (from 55.0% in 2002 to 47.8% in 2014; p<0.001) and by 3.0% among persons aged 18−25 years (from 77.4% in 2002 to 74.9% in 2014; p<0.001). The prevalence of perceived availability of marijuana increased by 8.0% (from 54.9% in 2002 to 59.2% in 2014; p<0.001) among persons aged ≥26 years (Table 8).
Mode of Acquisition
In 2014, the estimated national prevalence of self-reported modes of marijuana acquisition among past year marijuana users aged ≥12 years was bought it (48.4%), traded something for it (1.1%), got it for free or shared with someone else (49.3%), and grew it yourself (1.2%). From 2002 to 2014, the prevalence of modes of acquisition increased by 20.0% when bought it was reported (from 40.4% in 2002 to 48.4% in 2014; p<0.001), increased by 100% when grew it yourself was reported (from 0.6% in 2002 to 1.2% in 2014; p<0.001), and decreased by 14.0% when got it for free or shared with someone else was reported (from 57.6% in 2002 to 49.3% in 2014; p<0.001) among persons aged ≥12 years. Furthermore, a linear increase in the prevalence of modes of acquisition was observed in the majority of age groups when bought it and grew it yourself were reported. In contrast, a linear decrease in the prevalence of modes of acquisition was observed in all age groups when got it for free or shared with someone else were reported (Table 8).
Marijuana Dependence and Abuse
In 2014, the estimated national prevalence of past year marijuana dependence and abuse among all persons aged ≥12 years and past year marijuana users aged ≥12 years was 1.6% and 11.9%, respectively. From 2002 to 2014, the prevalence of past year marijuana dependence and abuse decreased by 11.0% among all persons aged ≥12 years (from 1.8% in 2002 to 1.6% in 2014; p<0.001) and 29.0% (from 16.7% in 2002 to 11.9% in 2014; p<0.001) among past year marijuana users aged ≥12 years. In general, a linear decrease was observed in the prevalence of past year marijuana dependence and abuse among all persons aged ≥12 years (Table 9) and past year marijuana users (Table 10) in the majority of age groups.
Marijuana Possession–Criminal Justice
In 2014, the estimated national prevalence of self-reported perceived maximum legal penalty for first offense possession of an ounce or less of marijuana for own use among persons aged ≥12 years was a fine (36.3%), probation (16.7%), community service (7.1%), possible prison sentence (27.3%), mandatory prison sentence (4.8%), and no penalty (7.9%). From 2002 to 2014, the prevalence of self-reported perceived maximum legal penalty for first offense possession of an ounce or less of marijuana for own use increased by 25.0% for a fine (from 29.1% in 2002 to 36.3% in 2014; p<0.001) and by 119.0% for no penalty¶ (from 3.6% in 2006 to 7.9% in 2014; p<0.001). In contrast, the prevalence of perceived maximum legal penalty for first offense possession of an ounce or less of marijuana for own use decreased by 6.0% for probation (from 17.8% in 2002 to 16.7% in 2014; p<0.001), by 23.0% for community service (from 9.2% in 2002 to 7.1% in 2014; p<0.001), by 26.0% for possible prison sentence (from 37.0% in 2002 to 27.3% in 2014; p<0.001), and by 30.0% for mandatory prison sentence (from 6.9% in 2002 to 4.8% in 2014; p<0.001). In general, a linear increase in the prevalence of perceived maximum legal penalty of a fine and no penalty was observed in all age groups. In contrast, a linear decrease in perceived maximum legal penalty of probation, community service, possible prison sentence, and mandatory prison sentence was observed in the majority of age groups (Table 11).
Discussion
This report represents, for the first time, an overview of national estimates for marijuana use and other related indicators among the U.S. noninstitutionalized civilian population aged ≥12 years using 2002–2014 NSDUH data. The report includes at least seven important findings. First, in 2014, a total of 2.5 million persons aged ≥12 years had used marijuana for the first time during the preceding 12 months, an average of approximately 7,000 new users each day. Second, during 2002–2014, the prevalence of marijuana use during the past month, past year, and daily or almost daily increased among persons aged ≥18 years, but not among those aged 12–17 years. Third, among persons aged ≥12 years, the prevalence of perceived great risk from smoking marijuana once or twice a week and once a month decreased and the prevalence of perceived no risk increased. Fourth, the prevalence of past year marijuana dependence and abuse decreased, except among persons aged ≥26 years. Fifth, among persons aged ≥12 years, the percentage reporting that marijuana was fairly easy or very easy to obtain increased. Sixth, the percentage of persons aged ≥12 years reporting the mode of acquisition of marijuana was buying it and growing it increased versus getting it for free and sharing it. Finally, the percentage of persons aged ≥12 years reporting that the perceived maximum legal penalty for the possession of an ounce or less of marijuana in their state is a fine and no penalty increased versus probation, community service, possible prison sentence, and mandatory prison sentence.
During 2002–2014, national estimates for marijuana use have decreased, specifically the past month, past year, and daily or almost daily marijuana use and past year new initiates among the U.S. population aged 12–17 years. Concurrently, state laws and policies regarding medical or recreational marijuana use have changed (13). Although these behavioral changes in the U.S. population are temporally related to the implementation of new state laws and policies, findings cannot be used to infer causality. Legalization of recreational marijuana in some states is relatively recent, and continued monitoring of marijuana use and frequency of use among youth is needed because these effects might be delayed. Use patterns among youth do not yet provide an accurate reflection of how legalization in some states will affect national estimates on marijuana use. In the interim, additional evaluation might determine that community-based substance use prevention efforts have contributed to this decline.
Since 2002, the prevalence of marijuana use and initiation among U.S. youth has declined. However, findings also indicate that among youth and adults, the prevalence of perceived great risk from smoking marijuana has steadily decreased and the prevalence of perceived no risk from smoking marijuana once or twice a week and month has increased. In previous national survey analyses, perception of risk has been inversely associated with prevalence of use (14–17). The data in this report document that the inverse association between perception of great risk from smoking marijuana and prevalence of use was observed only among adults. The fact that this inverse association was not found among youth is notable, given the hypothesis that legalization of medical and recreational marijuana use could lead to increases in youth initiation. One possible explanation could be that changes in state laws might require more time to be reflected in measurable national changes in use among youth. In addition, despite increased perceptions of no risk from smoking marijuana, obtaining marijuana nationally remains more difficult for persons aged 12−17 years than for those aged ≥18, which could explain the lower prevalence of marijuana use and initiation in this age group. In fact, since 2002 the perceived availability (i.e., fairly easy or very easy to obtain marijuana) among persons aged 12–17 and 18–25 years has decreased. However, more local or regional surveillance data are needed to better understand how retail legalization might affect accessibility. Identifying and implementing policies that continue to restrict youth access to marijuana remain important. Ongoing public health prevention efforts are warranted to prevent increases in marijuana initiation and use among youth.
Although NSDUH data suggest increases in daily and almost daily use among adults (both in the overall population and among adult marijuana users), they also suggest steady decreases in the prevalence of marijuana dependence and abuse among adult marijuana users since 2002. Typically, increased prevalence of marijuana use has been linked to increased prevalence of marijuana dependence or abuse (17). These findings suggest that refined measures of frequency (e.g., number of times per day, week, month, or year) of use might be needed to better quantify how often and what types of products (e.g., inhaled, eaten, infused, drank) persons are using to better estimate and understand marijuana consumption in the United States. With changes in medical marijuana laws (13) and, in particular, state laws or policies allowing limited access to low percentages of delta-9-tetrahydrocannabinol (THC) or cannabidiol (CBD), persons who use marijuana daily for medical reasons might be using strains that pose lower risk for dependence or abuse. As marijuana use becomes more commonplace, different patterns of use behavior might account for a substantial proportion of the increase in marijuana use among persons aged ≥18 years. Therefore, more research and surveillance data on marijuana use, frequency of use, and dependence are warranted.
Public Health Implications
Reducing Marijuana Use Among Youth
Heavy or frequent marijuana use has a negative effect on cognitive development, academic achievement, and other health risk behaviors among youth (2–8). Therefore, strategies to prevent youth access and use are still needed. Under the Controlled Substances Act** marijuana is still considered an illegal Schedule I drug. However, since 1996, approximately 40 states have legalized marijuana or allowed the use of products containing CBD, a less-psychoactive compound of the cannabis plant, for medical conditions, retail sales, or both (four states have legalized retail marijuana sales, the District of Columbia has legalized personal use and home cultivation, 23 states and the District of Columbia have legalized medical marijuana use, and 17 states have legalized CBD use) (13). In 2013, the U.S. Department of Justice issued guidance†† on enforcement priorities that included preventing the distribution of marijuana to minors. Although recent trend data from NSDUH regarding marijuana use at the aggregate national level provides some short-term reassurance that national-level increases in use among persons aged 12–17 years have not yet resulted from the policy change, any reassurance is tempered by the knowledge that this situation might not be stable. Changes allowing for legal medical or recreational marijuana use, combined with the decreased prevalence of perceived great risk from smoking marijuana, potentially could lead to increased use patterns in other age groups. In addition, a study of confiscated marijuana by the Drug Enforcement Administration indicated an increase in potency (i.e., higher levels of THC, the psychoactive compound) of the cannabis plant, potentially posing higher risk for adverse health consequences from marijuana use, particularly among youth (18). Given the variability of state-level legalization of medical and recreational marijuana (13) and the increased potency of the marijuana plant (18), improved surveillance and increased attention to public health prevention strategies are warranted at the federal, state, and local levels. Regardless of whether legalization of medical and recreational marijuana expands or diminishes, public health and other organizations can consider important steps (e.g., educational and prevention activities) to minimize health harms.
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