What happened when cannabis was legalised in the US?

This episode of The Lancet Voice explores the profound societal, health, and policy shifts resulting from the legalization of cannabis in the United States over the past two decades. Hosted by Niall Boyce and Miriam, with expert insights from Professor Deborah Hassan of Columbia University, the discussion traces the evolution from California's 1996 medical cannabis legalization to the current landscape where over 80% of U.S. states permit medical use and about 25 allow recreational access. Despite federal prohibition, state-level action has driven a cultural and commercial transformation, with cannabis now widely available in licensed dispensaries and increasingly normalized in public life—particularly in cities like New York. However, this shift has brought significant public health concerns, including rising rates of cannabis use disorder, increased risk of psychosis among vulnerable populations, and emerging conditions like cannabinoid hyperemesis syndrome. The episode also highlights critical gaps in regulation, such as the absence of standardized labeling, FDA oversight, and reliable roadside testing for impaired driving. While some benefits are noted—such as reduced opioid use and fewer cannabis-related arrests—the overall picture is complex, with evidence suggesting that legalization has amplified both access and risk, especially among adults with psychiatric or chronic pain conditions. The conversation underscores the urgent need for better research, particularly through rescheduling cannabis to allow more rigorous clinical trials. Professor Hassan reflects on her own journey from initial support for legalization to a more cautious stance, driven by data showing real harms. The episode concludes with a call for balanced, evidence-based public education and healthcare provider guidance, emphasizing that the U.S. is conducting a massive, real-world social experiment with long-term implications. With national surveys continuing to provide vital data, the hope is that future analysis will offer clearer insights into the true balance of harms and benefits, even as political and cultural divides persist across states.