Recent rapid decrease in adolescents’ perception that marijuana is harmful, but no concurrent increase in use

Highlights

• Perception that marijuana is not harmful has increased rapidly among adolescents.

• The large shift in perception was not accompanied by increased marijuana use.

• Practices of predicting adolescent marijuana use trends should be updated.

Abstract

Background

National trends in adolescent’s marijuana risk perceptions are traditionally used as a predictor of concurrent and future trends in adolescent marijuana use. We test the validity of this practice during a time of rapid marijuana policy change.

Methods

Two repeated cross-sectional U.S. nationally-representative surveys of 8th, 10th, and 12th-graders: Monitoring the Future (MTF) (1991–2015; N = 1,181,692) and National Survey on Drug Use and Health (NSDUH) (2002–2014; N = 113,317). We examined trends in the year-to-year prevalence of perceiving no risk of harm in using marijuana regularly, and prevalence of regular marijuana use within the previous month. A piecewise linear regression model tested for a change in the relationship between trends. Similar analyses examined any past-month use and controlled for demographic characteristics.

Results

Among MTF 12th-graders, the prevalence of regular marijuana use and risk perceptions changed similarly between 1991 and 2006 but diverged sharply afterward. The prevalence of regular marijuana use increased by ∼1 percentage point to 6.03% by 2015. In contrast, the proportion of 12th-graders that perceived marijuana as posing no risk increased over 11 percentage points to 21.39%. A similar divergence was found among NSDUH 12th-graders and other grades, for any past month marijuana use, and when controlling demographic characteristics.

Conclusions

An increase in adolescent marijuana use has not accompanied recent rapid decreases in marijuana risk perceptions. Policy makers may consider broader prevention strategies in addition to targeting marijuana risk perceptions. Further monitoring of predictors of marijuana use trends is needed as states legalize recreational marijuana use.

Introduction

In November 1996, California passed the first U.S. state law legalizing marijuana for medical use. Less than a year later, General Barry R. McCaffrey, Director of the Office of National Drug Control Policy (ONDCP), testified before the Senate Judiciary Committee on the Medical Marijuana Referenda Movement:

“Whether intended or not, permitting the ‘medical’ use of smoked marijuana will send the false and powerful message to our adolescents that marijuana use is beneficial. If pot is medicine, teenagers will rightfully reason, how can it hurt you?⋯No one should make the mistake of believing that increased societal acceptance of marijuana will not cause drug abuse to increase among our children” U.S. Congress House Committee on the Judiciary Subcommittee on Crime (1997).

The perceived harmfulness of marijuana is frequently cited as one of the most important protective factors preventing use among adolescents (Janz and Becker, 1984; Keyes et al., 2016; Piontek et al., 2013; Schmidt et al., 2016), which may pose deleterious risks to their health (Volkow et al., 2014) including addiction (Chen et al., 2009), altered brain development (Meier et al., 2012; Zalesky et al., 2012) and poor educational outcomes (Lynskey and Hall, 2000; Maggs et al., 2015), especially when use is frequent, i.e. nearly daily. During the decade after the ONDCP was established in 1988, increasing the perceived harmfulness of illicit drugs was the focus of multi-billion dollar national media campaigns (mandated by the National Narcotics Leadership Act of 1987) The National Youth Anti-Drug Media Campaign (1999) as well as large school-based substance use prevention programs (e.g., D.A.R.E.) (Rosenbaum, 2007). The Monitoring the Future Study – an ongoing national study of high school youth, launched in 1975 with the support of the National Institute of Drug Abuse director and former ONDCP director Robert Dupont – provided the earliest evidence of a strong inverse relationship between national trends in perceived harmfulness and marijuana use during the last quarter of the 20th century (Bachman et al., 1998; Bachman et al., 1988; Johnston et al., 1981). The national level of the perceived harmfulness of marijuana has been viewed as an important policy lever by law-makers and government executives (U.S. Congress House Committee on Education and Labor, 1986; U.S. Congress House Committee on the Judiciary Subcommittee on Crime, 1997; The National Youth Anti-Drug Media Campaign, 1999; Effectiveness of the National Youth Anti-Drug Media Campaign, 2000; Executive Office of the President of the United States, 2015).

However, since General McCaffrey’s testimony in 1997, the legal context of U.S. marijuana use has changed dramatically. Twenty-eight states have now passed laws permitting individuals to receive marijuana for medical purposes legally, and as of 2016, eight of these states and the District of Columbia have additionally legalized adult recreational marijuana use. During these times of shifting legal policies towards marijuana, previous assumptions about the relationship between trends in the perceived harmfulness of marijuana and trends in adolescent use may no longer hold. One study recently observed divergence between trends in marijuana risk perceptions and marijuana use in Washington State (Fleming et al., 2016) but this relationship in the trends had not been systematically evaluated at the national level. In addition, the way in which perceived harm relates to marijuana use at the individual level may be changing. A recent study (Miech et al., 2017) concluded this relationship between perceived harm and any marijuana use was similar by year across the last two decades but did not consider more intense, risky levels of use.

National trends in adolescent marijuana use and risk perceptions are documented yearly in reports by the Monitoring the Future study (MTF) (Johnston et al., 2016a, Johnston et al., 2016b) and the National Survey on Drug Use and Health (NSDUH) (Center for Behavioral Health Statistics and Quality, 2015b; Lipari et al., 2015). In the present study, using these two independent nationally representative samples of adolescents as replicable evidence, we directly examined whether the relationship between trends in perceived harmfulness of marijuana and concurrent trends in marijuana use has changed among high school seniors, a key transitional age representing the culmination of secondary school-based and parent-oriented substance use prevention efforts. Because of the potential differences in risk factors of marijuana use associated with the last year of high school, possibly due to preparation for college (Chen et al., 2016), we similarly examine whether these relationships have also changed for 8th and 10th-graders.