Quarterly trends in past-month cannabis use in the United States, 2015-2019.

Background: Prevalence of cannabis use has been increasing among select subgroups in the US; however, trend analyses typically examine prevalence of use across years. We sought to determine whether there is seasonal variation in use.

Methods: We conducted a secondary analysis of the National Survey on Drug Use and Health, a repeated cross-sectional survey of nationally representative probability samples of noninstitutionalized populations age ≥12 in the US. Quarterly trends in any past-month cannabis use were estimated using data from 2015-2019 (N = 282,768).

Results: Prevalence of past-month cannabis use increased significantly from 2015 to 2019 from 8.3%-11.5%, a 38.2 % increase (P < 0.001). Prevalence increased across calendar quarters on average from 8.9 % in January-March to 10.1 % in October-December, a 13.0 % increase (P < 0.001). Controlling for survey year and participant demographics, each subsequent quarter was associated with a 6% increase in odds for use (aOR=1.06, 95 % CI: 1.04-1.07). There were significant increases by quarter among all subgroups of sex, race/ethnicity, education, and among most adult age groups (Ps<0.05), with a 52.7 % increase among those age ≥65. Prevalence also significantly increased among those without a medical cannabis prescription and those not proxy-diagnosed with cannabis use disorder (Ps<0.01), suggesting recreational use may be driving increases more than medical or more chronic use. Those reporting past-year LSD or blunt use in particular were more likely to report higher prevalence of use later in the year (a 4.9 % and 3.3 % absolute increase, respectively; Ps<0.05).

Conclusion: The prevalence of cannabis use increases throughout the year, independently of annual increases.