Synthetic cannabinoid poisonings and access to the legal cannabis market: findings from US national poison centre data 2016-2019

Aim To investigate trends in synthetic cannabinoid exposures reported to United States (US) poison control centres, and their association with status of state cannabis legalisation. Methods A retrospective study of National Poison Data System (NPDS) data from 2016 to 2019 identified and associated synthetic poisoning reports with annual state cannabis law and market status. State status was categorised as restrictive (cannabis illegal or limited medical legalisation), medical (allowing THC-containing medical cannabis use) and permissive (allowing non-medical use of THC-containing cannabis by adults). We categorised a subset of states with permissive policies by their implementation of legal adult possession/use and opening retail markets, on a quarterly basis. Mixed-effects Poisson regression models assessed synthetic exposures associated with legal status, first among all states using annual counts, and then among states that implemented permissive law alone using quarterly counts. Results A total of 7600 exposures were reported during the study period. Overall, reported synthetic exposures declined over time. Most reported exposures (64.8%) required medical attention, and 61 deaths were documented. State implementation of medical cannabis law was associated with 13% fewer reported annual exposures. Adoption of permissive state cannabis policy was independently and significantly associated with 37% lower reported annual synthetic exposures, relative to restrictive policies (IRR: 0.63, 95% CI: 0.50-0.79). Among states with permissive law during the period, implementation of legal adult possession/use was associated with 22% fewer reported quarterly exposures. Opening of retail markets was associated with 36% fewer reported exposures, relative to states with medical cannabis only. Conclusions Adoption of permissive cannabis law was associated with significant reductions in reported synthetic cannabinoid exposures. More permissive cannabis law may have the unintended benefit of reducing both motivation and harms associated with use of synthetic cannabis products.