ImportanceWhether state implementation of medical and recreational cannabis laws is associated with increased cannabis use disorder (CUD) and/or cannabis poisoning among adults is not evident.ObjectiveTo examine state-level medical and recreational cannabis laws’ associations with CUD and cannabis poisoning, overall and by sex and age subgroups.Design, Setting, and ParticipantsIn this longitudinal cohort study, state-level CUD and cannabis poisoning diagnoses from January 2011 to December 2021 were examined across all 50 US states and the District of Columbia before and after the implementation of medical and recreational cannabis laws (MCLs and RCLs, respectively) using a staggered adoption difference-in-differences approach. Event studies were conducted to estimate the magnitude of the association for each year-quarter relative to the time of each policy implementation. This study was conducted among all adults aged 18 to 64 years enrolled in the Merative MarketScan Commercial Claims and Encounters Database, a database of employer-sponsored health insurance enrollees, with 1 year or more of continuous enrollment from 2011 to 2021. Data analysis was performed from January to August 2024.ExposuresState implementation of an MCL, opening a medical cannabis dispensary (MCD), allowing home cultivation of medical cannabis (HC-MC), and passage of an RCL.Main Outcomes and MeasuresCUD and cannabis poisoning diagnoses per 100 000 enrollees per quarter.ResultsThis study included 110 256 536 enrollees, of whom 56 843 030 (52%) were female and the mean (SD) enrollee age was 41.0 (13.5) years. MCLs were associated with significant increases in CUD and cannabis poisoning by 31.09 (95% CI, 20.20-41.99; P < .001) and 0.76 (95% CI, 0.52-1.00; P < .001) diagnoses per 100 000 enrollees per quarter, respectively, and RCLs were associated with a significant increase in cannabis poisoning by 0.34 (95% CI, 0.19-0.48; P < .001) per 100 000 enrollees per quarter in states with RCLs compared to states without these laws. No significant associations were observed for MCDs or HC-MC. Relative increases in CUD associated with MCLs were higher among female enrollees and among enrollees aged 35 to 44 years compared with male enrollees and other age groups, respectively. Sensitivity analysis results of 2011 to 2019 data were consistent with the 2011 to 2021 results.Conclusions and RelevanceIn this longitudinal cohort study, MCLs were associated with increased CUD and cannabis poisoning diagnoses, and RCLs were associated with increased cannabis poisoning in adults aged 18 to 64 years with employer-sponsored health insurance. Communities with increased access to cannabis may experience increased health care use and costs due to increases in cannabis poisoning and CUD, and new clinical and policy interventions are needed to curb these rising diagnoses.