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Cumulative frequency of policy changes by US state. Photo credit: UC San Diego Health Sciences
The study period coincided with significant policy reforms on substance use. In 2012, Colorado became the first U.S. state to permit recreational cannabis use, and by 2023, 24 states had followed suit, encompassing half of the U.S. adult population. Additionally, eight states had cities or counties decriminalize psychedelic use, and two states legalized psychedelic-assisted therapy and decriminalized psychedelics statewide.
Using a dynamic event-time difference-in-difference model, the researchers assessed the causal effects of these policy changes. They used the year before a policy enactment as the reference and states that never adopted the policy as controls. Separate analyses for cannabis and psychedelic policies measured microdosing searches per 10 million Google queries, examining annual and monthly changes in search rates across the U.S.
The results showed that policies reducing criminal penalties for psychedelic and cannabis use were associated with increased interest in microdosing, with the largest increases occurring in states with the most permissive policies, such as Oregon and Colorado. By 2023, these policy reforms accounted for over a quarter of the differences in monthly microdosing search rates across states.
The study also examined trends in terms related to microdosing, such as substances commonly used for microdosing. Between 2015 and 2018, LSD was the top term related to the microdosing, while from 2019 to 2023, mushrooms were most frequently searched. Other terms included Adderall, cannabis, CBD, DMT, ketamine, and MDMA.