Adolescent Cannabis Use After Cannabis Legalization and the COVID-19 Pandemic

Kelly C Young-Wolff; Natalie E Slama; Rosalie Liccardo Pacula; Alisa A Padon; Lynn D Silver; Stacy A Sterling; Derek D Satre; Cynthia I Campbell; Monique B Does; Stacey E Alexeeff

doi:10.1001/jamanetworkopen.2026.7720

. 2026 Apr 17;9(4):e267720. doi: 10.1001/jamanetworkopen.2026.7720

Adolescent Cannabis Use After Cannabis Legalization and the COVID-19 Pandemic

Kelly C Young-Wolff ^1,^2,^✉, Natalie E Slama ¹, Rosalie Liccardo Pacula ^3,⁴, Alisa A Padon ⁵, Lynn D Silver ⁵, Stacy A Sterling ^1,², Derek D Satre ^1,², Cynthia I Campbell ^1,², Monique B Does ¹, Stacey E Alexeeff ¹

¹Division of Research, Kaiser Permanente Northern California, Pleasanton

²Department of Psychiatry and Behavioral Sciences, University of California, San Francisco

³Institute for Addiction Science, University of Southern California, Los Angeles

⁴Leonard D. Schaeffer Center for Health Policy and Economics, Sol Price School of Public Policy, University of Southern California, Los Angeles

⁵Public Health Institute, Oakland, California

Accepted for Publication: February 24, 2026.

Published: April 17, 2026. doi:10.1001/jamanetworkopen.2026.7720

Open Access: This is an open access article distributed under the terms of the CC-BY-NC-ND License, which does not permit alteration or commercial use, including those for text and data mining, AI training, and similar technologies. © 2026 Young-Wolff KC et al. JAMA Network Open.

^✉

Corresponding Author: Kelly C. Young-Wolff, PhD, MPH, Division of Research, Kaiser Permanente Northern California, 4480 Hacienda Dr, Pleasanton, CA 94588 (kelly.c.young-wolff@kp.org).

Author Contributions: Dr Young-Wolff had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Young-Wolff, Pacula, Padon, Silver, Sterling, Alexeeff.

Acquisition, analysis, or interpretation of data: Slama, Pacula, Padon, Sterling, Satre, Campbell, Does, Alexeeff.

Drafting of the manuscript: Young-Wolff, Slama, Padon, Alexeeff.

Critical review of the manuscript for important intellectual content: Young-Wolff, Pacula, Silver, Sterling, Satre, Campbell, Does, Alexeeff.

Statistical analysis: Slama, Pacula, Alexeeff.

Obtained funding: Young-Wolff, Pacula, Padon, Campbell.

Administrative, technical, or material support: Sterling, Campbell, Does.

Supervision: Young-Wolff.

Conflict of Interest Disclosures: Dr Pacula reported receiving grants from National Institute on Drug Abuse (NIDA) and National Institute on Alcohol Abuse and Alcoholism (NIAAA) outside the submitted work. Dr Padon reported receiving grants from California Department of Public Health, California Department of Cannabis Control, and Tobacco-Related Disease Research Program outside the submitted work. Dr Campbell reported receiving research support from PMR Consortium outside the submitted work. Ms Does reported receiving research support from PMR Consortium outside the submitted work. No other disclosures were reported.

Funding/Support: This study was supported by a grant No. R01 DA0531920 from NIDA.

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Data Sharing Statement: See Supplement 2.

^✉

Corresponding author.

PMCID: PMC13090854 PMID: 41996112

Key Points

Question

Did rates of adolescent cannabis use in northern California change after recreational cannabis legalization or the COVID-19 pandemic?

Findings

This cross-sectional study of 1 308 655 questionnaires from adolescents universally screened for past-year cannabis use during standard well-child visits from 2011 to 2024 found that rates of adolescent cannabis use increased after recreational cannabis legalization passage and continued to increase after implementation of legal retail sales, then decreased after the COVID-19 pandemic.

Meaning

These findings suggest that adolescent cannabis use was sensitive to broader changes in cannabis policy and societal disruptions, including the COVID-19 pandemic.

This cross-sectional study examines how rates of adolescent cannabis use in California changed after recreational cannabis legalization and the COVID-19 pandemic.

Abstract

Importance

Understanding how cannabis legalization and large-scale societal disruptions influence adolescent cannabis use is important, as early use is associated with adverse health and educational outcomes. California has the largest regulated cannabis market in the US and provides a unique context to study how major policy and societal shifts are associated with adolescent cannabis use.

Objective

To examine how rates of adolescent cannabis use in California changed after recreational cannabis legalization (RCL) and the COVID-19 pandemic.

Design, Setting, and Participants

This population-based time-series cross-sectional study included adolescents aged 13 to 17 years in a large, integrated health care delivery system in California who were universally screened for cannabis use during standard pediatric care from January 2011 to December 2024. Data were analyzed from March to September 2025.

Exposures

California state RCL passage (November 9, 2016), which reduced penalties for underage possession of cannabis; implementation of legal sales of cannabis for adults (January 1, 2018); and the COVID-19 pandemic (March 19, 2020).

Main Outcomes and Measures

Any cannabis use in the past-year, self-reported based on universal screening at standard pediatric well-child visits. Interrupted time series analyses were fit using Poisson regression, standardized for sociodemographic characteristics of the adolescent Kaiser Permanente Northern California population.

Results

The study included 1 308 655 screening questionnaires completed over the 14-year study period (mean [SD] 7789 [3673] adolescent screenings per month), with a mean (SD) age of 15.0 (1.4) years at screening and 666 881 (51.0%) questionnaires from female participants. Before RCL passage, the mean rate of adolescent cannabis use was decreasing, from 10.39% (95% CI, 9.96%-10.82%) in January 2011 to 6.83% (95% CI, 6.54%-7.14%) in October 2016 (annual trend rate ratio [RR], 0.93 [95% CI, 0.92-0.94] per year). Rates started increasing at the time of RCL passage (slope change RR, 1.19 [95% CI, 1.06-1.35]), and rates continued to increase after implementation of legal retail sales (annual trend RR, 1.06 [95% CI, 1.02-1.11] per year). After the COVID-19 pandemic began, rates of adolescent cannabis use decreased substantially (level change RR, 0.86 [95% CI, 0.76-0.97]; slope change RR, 0.80 [95% CI, 0.70-0.91]). Rates of adolescent cannabis use continued to decrease slightly in the years after COVID-19, reaching a mean of 6.45% (95% CI, 6.15%-6.77%) in December 2024 (annual trend RR, 0.98 [95% CI, 0.96-0.997] per year).

Conclusions and Relevance

In this large, retrospective cross-sectional study, adolescent cannabis use increased following RCL and decreased following the COVID-19 pandemic, returning to prelegalization rates by 2024. These results have important implications for clinicians and policymakers and could help estimate future changes in adolescent cannabis use in response to broad policy changes and societal shifts and inform more effective prevention strategies.

Introduction

Cannabis is the most commonly used federally illicit substance among US adolescents¹ and is associated with adverse educational, neurodevelopmental, mental health, substance use, and physical health outcomes.^{2,3,4,5,6,7,8,9,10} Adolescent substance use is impacted by environmental factors, such as accessibility and acceptability of substance use, parent and peer use, and structural economic factors.^11,12,13 It is critical to understand how broader changes in cannabis policy and societal disruptions, like the COVID-19 pandemic, impact adolescent cannabis use to inform more effective policy, prevention, and early intervention programs.

Recreational cannabis legalization (RCL) for adults aged 21 years and older is typically put into effect in 2 parts: immediate legal changes at the time of law passage, such as decriminalization and legalized home grow, and a later full implementation when adult legal sales at storefronts begin. RCL could unintentionally influence adolescent cannabis use both at the time of passage, through normalization or reduced penalties for underage possession, and at implementation, through increased access (via adults or purchasing with fake identification), marketing that further normalizes cannabis use, lower prices, and more diverse routes of administration (eg, vaping, edibles).^{14,15,16,17,18} However, despite the spread of state-level cannabis legalization across the US, the prevalence of adolescent cannabis use is declining nationally.¹⁹ Results from studies on RCL and adolescent cannabis use are heterogeneous and inconsistent,²⁰ with some finding no post-RCL increases in use,^21,22,23 others finding increases in use,¹⁴ and some finding rates of frequent use are either stable or increasing nationally after RCL.^24,25 A 2024 systematic review and meta-analysis²⁶ found that RCL was associated with modest increases in past-month cannabis use among youths, with relatively small changes among adolescents compared with young adults. These studies are typically limited by short follow-up periods, sometimes preceding full implementation, which restrict the ability to assess long-term outcomes or delayed outcomes, and often aggregate data across states, potentially masking important differences. Longitudinal studies that test the associations of state RCL with adolescent cannabis use with longer follow-up are needed to guide policy recommendations.

The COVID-19 pandemic and shelter-in-place orders led to statewide school closures and extended social isolation for children and adolescents, contributing to increased mental health risks, including depression, anxiety, and self-injury.^27,28,29 Cannabis retailers were deemed essential businesses in California during the pandemic, with record sales reported in 2020.³⁰ Yet, findings from studies examining the association of the COVID-19 pandemic with adolescent cannabis use are mixed, with some studies reporting postpandemic declines in use, others reporting postpandemic increases, and some finding no change.^31,32,33 Existing research has been limited by cross-sectional designs, short observation windows, and reliance on convenience samples. Furthermore, many states did not legalize recreational cannabis use until 2019 or later, making it particularly hard to differentiate legalization associations from pandemic associations. Yet, few studies have examined the associations of legalization or the pandemic with adolescent cannabis use separately, and we know little about how these factors intersect.

California has the largest cannabis market in the US^21,34 and legalized recreational cannabis use in 2016, providing a unique context to examine changes in adolescent cannabis use over time in relation to recreational cannabis legalization and the COVID-19 pandemic. This study uses 14 years of data from a large health care system in California with universal screening for adolescent cannabis use to directly address key gaps in the literature by testing whether rates of adolescent cannabis use changed following RCL and the COVID-19 pandemic.

Methods

The Kaiser Permanente Northern California (KPNC) institutional review board approved this project with a waiver of consent and authorization because study procedures meet Health Insurance Portability and Accountability Act requirements and 42 CFR Part 2 regarding medical records, and all KPNC members are informed upon enrollment in the health plan that their data may be used for research. We followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Setting and Study Population

KPNC is an integrated health care system that serves more than 4.6 million members representative of the insured population of northern California.³⁵ For this study, all adolescents aged 13 to 17 years with a valid address within KPNC’s 35-county catchment area who completed a teenage well-child questionnaire (TWCQ) as part of standard pediatric care during January 1, 2011, to December 31, 2024, were eligible (1 320 919 questionnaires from 729 813 adolescents) (eFigure 1 and eResults in Supplement 1). A total of 10 137 questionnaires (0.8%) missing self-reported past-year cannabis use were excluded. There were negligible differences in age, sex, race and ethnicity, and neighborhood deprivation index (NDI) among those included vs excluded due to missing data on past-year cannabis use (all standardized differences, <0.2) (eTable 1 in Supplement 1). For 526 adolescents (0.04%) with more than 1 questionnaire per month, we kept only the first response. Questionnaires completed by adolescents who were missing electronic health record (EHR) data on covariates were excluded (other or unknown sex: 873 individuals [0.07%]; NDI: 728 individuals [0.06%]).

Measures

Sociodemographics

Age, sex, and census-based NDI³⁶ from the home address at the time of the well-child questionnaire were obtained from the EHR. We categorized NDI into quartiles using cut points from the general insured KPNC population. We also included data on self-reported race and ethnicity (Hispanic and non-Hispanic: Asian, Black, White, and other [including Alaska Native, American Indian, Hawaiian Islander, and Pacific Islander], multiracial, unknown) as a social construct due to known differences in the prevalence of adolescent cannabis use by race and ethnicity.³⁷

Cannabis Use

KPNC conducts universal screenings for overall health (eg, diet, sleep) and sensitive health topics (eg, mental health and past-year substance use) among adolescents aged 13 to 17 years during pediatric well-child visits, following national guidelines. This TWCQ is completed solely by the adolescent, and includes a specific confidential question about cannabis use: “During the past year, did you use marijuana?”

Recreational Cannabis Legalization

We examined RCL passage and implementation. California voters passed RCL on November 9, 2016.³⁸ After RCL passage, medical use was further decriminalized, home cultivation and cannabis possession became legal for adults, and possession by minors was reduced to an infraction. RCL full implementation started when state-licensed recreational retailers began to open (January 1, 2018).

COVID-19 Pandemic

The COVID-19 pandemic began in March 2020. In California, 6 Bay Area counties announced shelter-in-place orders by March 16, 2020 and a statewide shelter-in-place order was issued on March 19, 2020.³⁹ The shelter-in-place mandate was lifted on January 25, 2021, but many schools were closed through April 2021.⁴⁰ In California, cannabis retailers were designated as essential businesses and remained open during the pandemic.

Statistical Analysis

Monthly rates of past-year cannabis use were standardized to the age, sex, race and ethnicity, and NDI distribution of the cumulative total monthly KPNC adolescent (age 13-17 years) membership during the study period (January 1, 2011, to December 31, 2024) to account for any differences in distributions of these sociodemographic characteristics over time.⁴¹ We conducted interrupted time series (ITS) analyses with segmented Poisson regression models accounting for overdispersion using the quasi-Poisson family.⁴² The outcome was the monthly count of questionnaires positive for past-year cannabis use, and the offset was the log of the standardized population count that month. We followed an established methodologic framework for defining the ITS model.⁴³ We first assessed the data prior to the first interruption for linearity, seasonality, and autocorrelation. Based on these preliminary models, all models included seasonal adjustment using Fourier terms.⁴⁴ Because the unit of analysis was the monthly rate of adolescent cannabis use over thousands of questionnaires, repeated questionnaires from the same adolescent separated by many months or years during the 14-year study period do not induce correlation in the monthly aggregated data.

The ITS analysis included 3 interruptions: RCL passage in 2016, RCL implementation in 2018, and the COVID-19 pandemic in 2020. The time periods were pre-RCL passage (January 2011 to October 2016), post-RCL passage and pre-RCL implementation (November 2016 to December 2017), post-RCL implementation and pre–COVID-19 (January 2018 to March 2020), and post–COVID-19 (June 2020 to December 2024). Data in March 2020 included adolescents primarily screened in the first half of March (99%), before the California statewide shelter in place mandate, and the months of April and May 2020 were excluded from the analyses due to sparsity (155 questionnaires [<0.1%]).

For the main model, we hypothesized level and slope increases at each interruption based on prior research showing post-RCL changes in adolescent cannabis use⁴⁵ and growth of licensed retailers after implementation.⁴⁶ We hypothesized a decrease in use after COVID-19 based on other published research.³³ We also hypothesized a lag shift following the onset of COVID-19 because the outcome was defined as past-year cannabis use, such that each monthly estimate continued to incorporate use during pre–COVID-19 months until sufficient time had elapsed. We modeled the lag shift in June 2021, a year after the initial COVID-19 interruption. We reported rate ratios (RRs) and 95% CIs for level and slope changes at each interruption relative to the previous time period, adjusted for the composition of age, sex, race and ethnicity, and NDI in the underlying adolescent study population via the standardization. Thus, the RRs are interpreted as relative changes in population-level cannabis use rates over time, adjusted for changes in the composition of the underlying adolescent study population.

We then assessed model fit using established model selection methods for ITS modeling.⁴³ We compared our hypothesized model to simpler models and compared model fit using the quasi-Akaike Information Criterion since ITS models were fit under the quasi-Poisson distribution. We also compared model fit of the timing of the post–COVID-19 lag shift. We selected the best fitting model and reported secondary results under this parsimonious model (eResults in Supplement 1). Results by age were estimated by including interaction terms with each year of age in the parsimonious ITS model.

We computed e-values as a sensitivity analysis to evaluate the potential impact of unmeasured confounding.^47,48 In descriptive tables, the standardized difference was calculated as the difference in proportions divided by the standard error.⁴⁹

Analyses were conducted in SAS version 9.4 (SAS Institute) and R version 4.3.1 (R Project for Statistical Computing) from March to September 2025. Two-sided P < .05 was considered statistically significant.

Results

The study included 1 308 655 questionnaires (mean [SD] age at screening, 15.0 [1.4] years; 666 881 [51.0%] female) over 14 years (mean [SD] 7789 [3463] adolescent screenings per month). The sample was racially and ethnically diverse, with 383 544 questionnaires (29.3%) from Hispanic adolescents, 267 031 questionnaires (20.4%) from non-Hispanic Asian adolescents, 104 670 questionnaires (8.0%) from non-Hispanic Black adolescents, 114 537 questionnaires (8.8%) from non-Hispanic adolescents with other, multiple, or unknown race(s), and 438 873 questionnaires (33.5%) from non-Hispanic White adolescents. Approximately half of adolescents in the sample completed more than 1 questionnaire during the study period (353 920 adolescents [48.7%] with 1 questionnaire; 220 228 adolescents [30.3%] with 2 questionnaires; 152 053 adolescents [21.0%] with ≥3 questionnaires). Overall, 97 235 questionnaires (7.4%) self-reported past-year cannabis use. Across the time periods, past-year cannabis use was reported in 41 657 of 522 037 questionnaires (8.0%) pre-RCL passage, 8184 of 112 069 questionnaires (7.3%) post-RCL passage and pre-RCL implementation, 19 111 of 228 634 questionnaires (8.4%) post-RCL implementation and pre–COVID-19, and 28 283 of 445 915 questionnaires (6.3%) post–COVID-19. There were negligible differences in age, sex, race and ethnicity, and NDI among the 4 time periods (all standardized differences <0.2) (Table 1).

Table 1. Baseline Characteristics of Questionnaires From Adolescents Screened for Past-Year Cannabis Use Between January 1, 2011, to December 31, 2024.

Characteristic	Questionnaires, No. (%)					Standardized difference^e
	Overall (N = 1 308 655)	Time period
	Overall (N = 1 308 655)	Pre-RCL passage (n = 522 037)^a	Post-RCL passage, pre-RCL implementation (n = 112 069)^b	Post-RCL implementation, pre–COVID-19 (n = 228 634)^c	Post–COVID-19 (n = 445 915)^d
Age, mean (SD), y	15.0 (1.4)	15.0 (1.4)	15.0 (1.4)	15.0 (1.4)	15.0 (1.4)	0.0
Sex
Female	641 774 (49.0)	257 332 (49.3)	55 057 (49.1)	112 022 (49.0)	217 363 (48.7)	0.0
Male	666 881 (51.0)	264 705 (50.7)	57 012 (50.9)	116 612 (51.0)	228 552 (51.3)	0.0
Race and ethnicity
Hispanic	383 544 (29.3)	160 674 (30.8)	32 883 (29.3)	65 047 (28.5)	124 940 (28.0)	0.09
Non-Hispanic
Asian	267 031 (20.4)	96 150 (18.4)	23 338 (20.8)	50 063 (21.9)	97 480 (21.9)
Black	104 670 (8.0)	46 707 (8.9)	8965 (8.0)	17 149 (7.5)	31 849 (7.1)
Other^f	114 537 (8.8)	38 044 (7.3)	8622 (7.7)	19 135 (8.4)	48 736 (10.9)
White	438 873 (33.5)	180 462 (34.6)	38 261 (34.1)	77 240 (33.8)	142 910 (32.0)
NDI, quartile
First (least deprivation)	293 461 (22.4)	89 532 (17.2)	24 150 (21.5)	56 055 (24.5)	123 724 (27.7)	0.15
Second	388 588 (29.7)	160 597 (30.8)	35 400 (31.6)	67 346 (29.5)	125 245 (28.1)
Third	352 516 (26.9)	146 479 (28.1)	29 180 (26.0)	61 484 (26.9)	115 373 (25.9)
Fourth (most deprivation)	274 090 (20.9)	125 429 (24.0)	23 339 (20.8)	43 749 (19.1)	81 573 (18.3)

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Abbreviations: NDI, Neighborhood Deprivation Index; RCL, recreational cannabis legalization.

^{^a}

January 1, 2011, to October 31, 2016.

^{^b}

November 1, 2016, to December 31, 2017.

^{^c}

January 1, 2018, to May 31, 2020.

^{^d}

June 1, 2020, to December 31, 2024.

^{^e}

Difference in means or proportions divided by standard error; imbalance defined as absolute value greater than 0.20 (small effect size).⁴⁹

^{^f}

Other includes American Indian, Alaska Native, Hawaiian Islander, Pacific Islander, multiracial, or unknown.

RCL Passage and Implementation

Figure 1 shows results for the main model, with numeric results presented in Table 2. Before RCL passage, rates of adolescent past-year cannabis use were decreasing from a mean of 10.39% (95% CI, 9.96%-10.82%) in January 2011 to 6.83% in October 2016 (95% CI, 6.54%-7.14%), just prior to RCL passage (annual trend RR, 0.93 [95% CI, 0.92-0.94]) (Figure 1). At the time of RCL passage there was a slope change in the rate of adolescent cannabis use (slope change RR, 1.19 [95% CI, 1.06-1.35]) but no level change (level change RR, 1.05 [95% CI, 0.95-1.15]) (Table 2). The mean rate of adolescent cannabis use reached 8.12% (95% CI, 7.51%-8.77%) in December 2017, just prior to RCL implementation.

Table 2. Model Terms and Annual Trends From the Interrupted Time Series Analysis.

Measure	RR (95% CI)	Pre vs post P value^a
Pre-RCL passage time trend, annual^b	0.93 (0.92-0.94)	NA
RCL passage
Level change	1.05 (0.95-1.15)	.32
Slope change, annual	1.19 (1.06-1.35)	.005
RCL implementation^c
Level change	1.02 (0.93-1.11)	.70
Slope change, annual	0.96 (0.84-1.09)	.48
COVID-19^d
Level change	0.86 (0.76-0.97)	.02
Slope change, annual	0.80 (0.7-0.91)	.001
Lagged slope change, annual	1.16 (1.01-1.32)	.04
Annual trend
Pre-RCL passage^b	0.93 (0.92-0.94)	NA
Post-RCL passage, pre-RCL implementation^c	1.11 (0.98-1.26)	NA
Post-RCL implementation, pre-COVID-19^d	1.06 (1.02-1.11)	NA
Post–COVID-19, pre–COVID-19 lag^e	0.85 (0.75-0.96)	NA
Post–COVID-19 lag^e	0.98 (0.96-0.997)	NA

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Abbreviations: NA, not applicable; RCL, recreational cannabis legalization; RR, rate ratio.

^{^a}

P value for level change or slope change.

^{^b}

January 1, 2011, to October 31, 2016.

^{^c}

November 1, 2016, to December 31, 2017.

^{^d}

January 1, 2018, to May 31, 2020.

^{^e}

June 1, 2020, to December 31, 2024.

The trend remained similar after RCL implementation in 2018, with an increasing trend in rates (RR, 1.06 [95% CI, 1.02-1.11] per year) and no statistically significant slope or level change (slope change RR, 1.00 [95% CI, 0.99-1.01]; level change RR, 1.02 [95% CI, 0.93-1.11]) (Figure 1 and Table 2). Two years after RCL implementation, just prior to the start of the COVID-19 pandemic, cannabis use rates had increased to a mean level of 9.45% (95% CI, 8.95%-9.98%).

COVID-19 Pandemic

After the COVID-19 pandemic began, rates of adolescent past-year cannabis use decreased. There was a level change (RR, 0.86 [95% CI, 0.76-0.97]) and slope change (RR, 0.98 [95% CI, 0.97-0.99]) (Table 2). During the lag period from June 2020 until June 2021, rates of adolescent cannabis use decreased to a mean rate of 6.97% (95% CI, 6.65-7.30) (annual trend RR, 0.85 [95% CI, 0.75-0.96]). After the lag period, rates of adolescent past-year cannabis use continued to decrease, although less sharply (annual trend RR, 0.98 [95% CI, 0.96-0.997], slope change RR, 1.01 [95% CI, 1.00-1.02]). At the end of the study period in December 2024, rates of adolescent past-year cannabis use reached a mean level of 6.45% (95% CI, 6.15%-6.77%).

Sensitivity Analyses

The best fitting parsimonious model based on quasi-Akaike Information Criterion did not include level changes at RCL passage and RCL implementation (eTable 2 in Supplement 1). Results from the parsimonious model were very similar to the main model (eResults, eFigure 2, and eTable 3 in Supplement 1). The e-values for the annual slope changes ranged from 1.27 to 1.82 in the main model and 1.44 to 1.82 in the parsimonious model (eTable 4 in Supplement 1). An unmeasured confounder would need to have at least associations of that magnitude with both the exposure and the outcome to fully explain the reported RRs. Since all exposures were time-series interruptions, the unmeasured confounder would need to be associated with the timing of the interruption.

Results by Age Group

Figure 2 shows the ITS results by age. Older adolescents had higher rates of past-year cannabis use throughout the study period. Relative changes in rates of use were similar across age groups for RCL passage, RCL implementation, and the COVID-19 pandemic (eTable 5 in Supplement 1).

Discussion

In this large, sociodemographically diverse cross-sectional time-series study of adolescents universally screened for past-year cannabis use during pediatric care, rates of cannabis use increased following RCL and decreased following the COVID-19 pandemic, returning to pre-RCL rates by 2024. The post-RCL increase in rates of adolescent cannabis use followed a prior decline and could be mediated by factors such as declining perceptions of harm or of legal risk, normalization, increased availability, exposure to advertising, reductions in cannabis prices, or greater exposure to nonsmoked or flavored modes of cannabis use (eg, vaping) that may be more appealing to adolescents.^{14,15,16,17,18} Adolescence is an important period of development when cannabis use is especially harmful. It is critical to monitor how changes in policy and broader social changes shape adolescent cannabis use to inform prevention and policy measures.

The increase in rates of adolescent past-year cannabis use following RCL is consistent with a 2024 meta-analysis²⁶ that found modest increases associated with RCL among more recent studies. Furthermore, a synthetic control analysis¹⁴ of state-level data from the National Survey on Drug Use and Health found that RCL was associated with an increased prevalence and initiation of adolescent cannabis use. Our results also align with studies showing pre-RCL declines in adolescent cannabis use⁴⁵ and post-RCL declines in the perceptions of harm and increases in use among adolescents in eighth and tenth grades.⁵⁰ Notably, our findings complement studies that have found post-RCL increases in adolescent cannabis-related harms, including cannabis use disorder,¹⁷ cannabis-related emergency department visits, cannabis-related hospitalization,⁵¹ and hospital encounters for psychosis.⁵⁰ However, not all studies report increased adolescent cannabis past-year use following RCL, highlighting the importance of contextual factors, such as state-specific local policies and social environments, which are not held fixed when doing analyses with data from multiple states.¹⁸

A key strength of our study is the differentiation between RCL passage and implementation when adult-use retailers were allowed to open. Prior studies have primarily relied on comparing the prevalence of adolescent cannabis use before and after RCL, comparing states with and without RCL, or using difference-in-difference models that do not account for the gap between law passage and implementation.²⁶ We found that rates of adolescent cannabis use increased at the time of RCL in northern California, even before adult-use stores opened, suggesting that changes in attitudes or beliefs may drive early increases. Reductions in legal consequences for underage possession may also have contributed. Notably, after RCL passage, only the slope change was statistically significant, indicating that increases in adolescent cannabis use unfolded gradually over time rather than as an abrupt response at the time of policy change. This pattern is consistent with gradual changes in attitudes and perceptions of harm, which differs from a level change that would suggest an immediate shift is use. These findings contrast with our prior study of pregnant individuals, where an immediate increase in prenatal cannabis use was found after implementation when adult-use stores opened.⁵² Taken together, these results underscore population-specific changes in cannabis use following RCL and highlight the need for further research to clarify the mechanisms through which RCL is associated with increased risk of adolescent cannabis use and whether risk varies by individual or local cannabis policy characteristics. Our findings support the importance of universal screening for adolescent cannabis use along with preventive strategies that address youth access and exposure following policy change.

Our study also found that rates of adolescent cannabis use declined following the onset of the COVID-19 pandemic. These findings are consistent with nationally representative US data, indicating that adolescent cannabis use dropped between 2020 and 2021 and after the COVID-19 pandemic and remained below prepandemic levels through 2024.³³ Notably, these declines occurred despite contemporaneous increases in adolescent mental health symptoms during the pandemic,²⁸ suggesting that changes in substance use were not driven by improvements in mental health. Prior studies suggest that pandemic-era declines in adolescent substance use, including alcohol, were explained primarily by social distancing and reduced social interactions, increased parental supervision, and reduced access to substances.^53,54 While these mechanisms may explain initial declines in cannabis use, continued low rates through 2024 suggest broader and more persistent social or cultural contextual factors. The pandemic-era decline in rates of adolescent cannabis use is particularly notable in the context of increases in use after the passage of RCL. Taken together, our results suggest that adolescent cannabis use shows temporal variation across environmental and structural contexts. These findings indicate that state-level policy evaluations may mask meaningful heterogeneity at the local level. Future research is needed to examine how local policy environments, such as municipal bans on storefront retailers and policies requiring additional buffers between retailers and schools, may influence patterns of cannabis use associated with RCL.

Strengths and Limitations

Strengths of our study included a large, sociodemographically diverse population of adolescents screened for cannabis use during standard pediatric well-child visits during a 14-year period that covered RCL passage, sales implementation, and the COVID-19 pandemic. Our study took place in California, where a mature medical cannabis market and relatively high baseline exposure allowed us to assess differences in adolescent cannabis use before and after legalization. Furthermore, we used a rigorous quasiexperimental design by applying interrupted time series, which directly models trends and overcomes limitations of difference-in-difference designs.

This study also has several limitations. Findings from KPNC adolescents may not generalize to uninsured adolescents, those who did not come in for routine care or did not complete the TWCQ, those outside of northern California, or those living in states where medical cannabis is illegal. As with any ITS analysis, inference relies on model assumptions that cannot be fully verified empirically, including correct specification of underlying secular trends and the absence of concurrent interventions. We do not have a concurrent control group to account for broader secular trends that may also be influencing adolescent cannabis use rates. Information on adolescent cannabis use was limited to any self-reported past-year cannabis use. Both dependence on self-report and measurement of only past-year use may underestimate true use. Adolescents’ willingness to disclose cannabis use may have changed following RCL, and differential reporting could have impacted findings. We measured any self-reported cannabis during the past year, and we did not have information about key aspects of cannabis use, including past–30-day use, use frequency, mode, product strength, or perceptions of cannabis-related harms. Several studies indicate that frequency of use or other factors, such as parental history of cannabis use, matter when considering associations between RCL and cannabis use.^55,56,57 Future studies that examine more detailed measures of adolescent cannabis use and include information about the local cannabis policy and retail environment are needed.

Conclusions

In this large, retrospective cross-sectional time-series study, adolescent cannabis use increased following RCL and decreased following the COVID-19 pandemic, returning to prelegalization rates by 2024. Additional research is needed to determine the specific mechanisms underlying these changes in use and whether these trends continue or change further over time. Yet, these findings have important implications for clinicians and policymakers and could help estimate future changes in adolescent cannabis use in response to broad policy changes and societal shifts and inform more effective prevention strategies.

Supplement 1.

eResults.

eTable 1. Comparison between adolescents included vs excluded due to missing self-reported past-year cannabis use

eTable 2. Main and additional models and QAIC

eTable 3. Model terms and annual trends from the interrupted time series analysis

eTable 4. E-values for the main and parsimonious interrupted time series analyses

eTable 5. Level and slope changes in the Interrupted time series analysis

eFigure 1. Participant enrollment flowchart

eFigure 2. Parsimonious model examining changes in rates of self-reported past-year cannabis use among adolescents aged 13 to 17 years

jamanetwopen-e267720-s001.pdf^{(433.8KB, pdf)}

Supplement 2.

Data Sharing Statement

jamanetwopen-e267720-s002.pdf^{(13.3KB, pdf)}

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplement 1.

eResults.

eTable 1. Comparison between adolescents included vs excluded due to missing self-reported past-year cannabis use

eTable 2. Main and additional models and QAIC

eTable 3. Model terms and annual trends from the interrupted time series analysis

eTable 4. E-values for the main and parsimonious interrupted time series analyses

eTable 5. Level and slope changes in the Interrupted time series analysis

eFigure 1. Participant enrollment flowchart

eFigure 2. Parsimonious model examining changes in rates of self-reported past-year cannabis use among adolescents aged 13 to 17 years

jamanetwopen-e267720-s001.pdf^{(433.8KB, pdf)}

Supplement 2.

Data Sharing Statement

jamanetwopen-e267720-s002.pdf^{(13.3KB, pdf)}

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[zoi260253r13] 13.Watts LL, Hamza EA, Bedewy DA, Moustafa AA. A meta-analysis study on peer influence and adolescent substance use. Curr Psychol. 2024;43(5):3866-3881. doi: 10.1007/s12144-023-04944-z [DOI] [Google Scholar]

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[zoi260253r15] 15.Hunt P, Pacula RL. Early impacts of marijuana legalization: an evaluation of prices in Colorado and Washington. J Prim Prev. 2017;38(3):221-248. doi: 10.1007/s10935-017-0471-x [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r16] 16.Smart R, Caulkins JP, Kilmer B, Davenport S, Midgette G. Variation in cannabis potency and prices in a newly legal market: evidence from 30 million cannabis sales in Washington state. Addiction. 2017;112(12):2167-2177. doi: 10.1111/add.13886 [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r17] 17.Cerdá M, Mauro C, Hamilton A, et al. Association between recreational marijuana legalization in the United States and changes in marijuana use and cannabis use disorder from 2008 to 2016. JAMA Psychiatry. 2020;77(2):165-171. doi: 10.1001/jamapsychiatry.2019.3254 [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r18] 18.Manthey J, Jacobsen B, Hayer T, et al. The impact of legal cannabis availability on cannabis use and health outcomes: a systematic review. Int J Drug Policy. 2023;116:104039. doi: 10.1016/j.drugpo.2023.104039 [DOI] [PubMed] [Google Scholar]

[zoi260253r19] 19.Miech RA, Johnston LD, Patrick ME, O’Malley PM. Monitoring the Future—National Survey Results on Drug Use, 1975–2024: Overview and Detailed Results for Secondary School Students. Institute for Social Research, University of Michigan; 2025. [Google Scholar]

[zoi260253r20] 20.Farrelly KN, Wardell JD, Marsden E, et al. The impact of recreational cannabis legalization on cannabis use and associated outcomes: a systematic review. Subst Abuse. Published online May 9, 2023. doi: 10.1177/11782218231172054 [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r21] 21.Athanassiou M, Dumais A, Zouaoui I, Potvin S. The clouded debate: a systematic review of comparative longitudinal studies examining the impact of recreational cannabis legalization on key public health outcomes. Front Psychiatry. 2023;13:1060656. doi: 10.3389/fpsyt.2022.1060656 [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r22] 22.Bailey JA, Tiberio SS, Kerr DCR, Epstein M, Henry KL, Capaldi DM. Effects of cannabis legalization on adolescent cannabis use across 3 studies. Am J Prev Med. 2023;64(3):361-367. doi: 10.1016/j.amepre.2022.09.019 [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r23] 23.O’Grady MA, Iverson MG, Suleiman AO, Rhee TG. Is legalization of recreational cannabis associated with levels of use and cannabis use disorder among youth in the United States: a rapid systematic review. Eur Child Adolesc Psychiatry. 2024;33(3):701-723. doi: 10.1007/s00787-022-01994-9 [DOI] [PubMed] [Google Scholar]

[zoi260253r24] 24.Coley RL, Carey N, Kruzik C, Hawkins SS, Baum CF. Recreational cannabis legalization, retail sales, and adolescent substance use through 2021. JAMA Pediatr. 2024;178(6):622-625. doi: 10.1001/jamapediatrics.2024.0555 [DOI] [PMC free article] [PubMed] [Google Scholar]

[zoi260253r25] 25.Hollingsworth A, Wing C, Bradford AC. Comparative effects of recreational and medical marijuana laws on drug use among adults and adolescents. J Law Econ. 2022;65(3):515-554. doi: 10.1086/721267 [DOI] [Google Scholar]

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PERMALINK

Adolescent Cannabis Use After Cannabis Legalization and the COVID-19 Pandemic

Kelly C Young-Wolff, PhD, MPH

Natalie E Slama, MPH

Rosalie Liccardo Pacula, PhD

Alisa A Padon, PhD

Lynn D Silver, MD, MPH

Stacy A Sterling, DrPH, MSW, MPH

Derek D Satre, PhD

Cynthia I Campbell, PhD, MPH

Monique B Does, MPH

Stacey E Alexeeff, PhD

Key Points

Question

Findings

Meaning

Abstract

Importance

Objective

Design, Setting, and Participants

Exposures

Main Outcomes and Measures

Results

Conclusions and Relevance

Introduction

Methods

Setting and Study Population

Measures

Sociodemographics

Cannabis Use

Recreational Cannabis Legalization

COVID-19 Pandemic

Statistical Analysis

Results

Table 1. Baseline Characteristics of Questionnaires From Adolescents Screened for Past-Year Cannabis Use Between January 1, 2011, to December 31, 2024.

RCL Passage and Implementation

Figure 1. Line Graph of Changes in Rates of Self-Reported Past-Year Cannabis Use Among Adolescents Aged 13 to 17 Years.

Table 2. Model Terms and Annual Trends From the Interrupted Time Series Analysis.

COVID-19 Pandemic

Sensitivity Analyses

Results by Age Group

Figure 2. Line Graph of Changes in Rates of Self-Reported Past-Year Cannabis Use by Age Among Adolescents Age 13 to 17 Years.

Discussion

Strengths and Limitations

Conclusions

References

Associated Data

Supplementary Materials

ACTIONS

PERMALINK

RESOURCES

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