Trends and age, period and cohort effects for marijuana use prevalence in the 1984-2015 US National Alcohol Surveys.

BACKGROUND AND AIMS

Epidemiological trends show marijuana use in the United States to have increased in recent years. Previous research has identified cohort effects as contributing to the rising prevalence, in particular birth cohorts born after 1945. However, given recent policy efforts to regulate marijuana use at the state level, period effects could also play a contributory role. This study aimed to examine whether cohort or period effects play a larger role in explaining trends in marijuana use.

DESIGN

Using data from seven National Alcohol Surveys, we estimated age-period-cohort decomposition models for marijuana use, controlling for socio-demographic measures.

SETTING

United States.

PARTICIPANTS

US general population aged 18 and older from 1984 to 2015.

MEASUREMENTS

Any past-year marijuana use.

FINDINGS

Results indicated that period effects were the main driver of rising marijuana use prevalence. Models including indicators of medical and recreational marijuana policies did not find any significant positive impacts.

CONCLUSIONS

The steep rise in marijuana use in the United States since 2005 occurred across the population and is attributable to general period effects not linked specifically to the liberalization of marijuana policies in some states.