ImportanceIt is unknown whether state recreational cannabis legalization (RCL) is related to increased rates of prenatal cannabis use or whether RCL-related changes vary with cannabis screening methods or the local policy environment.ObjectiveTo test whether RCL in California was associated with changes in prenatal cannabis use rates, whether changes were evident in both self-report and urine toxicology testing, and whether rates varied by local policies banning vs allowing adult-use retailers post-RCL.Design, Setting, and ParticipantsThis population-based time-series study used data from pregnancies in Kaiser Permanente Northern California universally screened for cannabis use during early pregnancy by self-report and toxicology testing from January 1, 2012, to December 31, 2019. Analyses were conducted from September 2022 to August 2024.ExposuresCalifornia state RCL passage (November 9, 2016) and implementation of legal sales (January 1, 2018) were examined with a 1-month lag. Local policies allowing vs banning medical retailers pre-RCL and adult-use retailers post-RCL were also examined.Main Outcomes and MeasuresAny prenatal cannabis use was based on screening at entrance to prenatal care (typically at 8-10 weeks’ gestation) and defined as (1) a positive urine toxicology test result or self-report, (2) a positive urine toxicology test result, or (3) self-report. Interrupted time series models were fit using Poisson regression, adjusting for age, race and ethnicity, and neighborhood deprivation index.ResultsThe sample of 300 993 pregnancies (236 327 unique individuals) comprised 25.9% Asian individuals, 6.4% Black individuals, 26.0% Hispanic individuals, 37.7% White individuals, and 4.1% individuals of other, multiple, or unknown race, with a mean (SD) age of 30.3 (5.4) years. Before RCL implementation, rates of prenatal cannabis use rose steadily from 4.5% in January 2012 to 7.1% in January 2018. There was no change in use rates at the time of RCL passage (level change rate ratio [RR], 1.03; 95% CI, 0.96-1.11) and a statistically significant increase in rates in the first month after RCL implementation, increasing to 8.6% in February 2018 (level change RR, 1.10; 95% CI, 1.04-1.16). Results were similar when defining prenatal cannabis use by (1) a toxicology test or (2) self-report. In local policy analyses, the post-RCL implementation increase in use was only found among those in jurisdictions allowing adult-use cannabis retailers (allowed RR, 1.21; 95% CI, 1.10-1.33; banned RR, 1.01; 95% CI, 0.93-1.10).Conclusions and RelevanceIn this time-series study, RCL implementation in California was associated with an increase in rates of cannabis use during early pregnancy, defined by both self-report and toxicology testing, driven by individuals living in jurisdictions that allowed adult-use retailers.
