Allysia Finley continues her campaign to resurrect reefer madness in her Weekend Interview with Bertha Madras (May 11). Ms. Finley overstates the significance of weak, observational studies to suggest that adults who use marijuana recreationally are at a high risk of developing mental-health problems.

Ms. Finley cites a new study in the International Journal of Drug Policy to imply that regular users risk developing violent behavior and schizophrenia. But the study concludes, “Research is needed to ascertain the directionality of the associations between cannabis use and violent behavior and underlying sex-specific mechanism(s).” Correlation doesn’t equal causation, and even the direction of the correlation was unclear.

Many countries saw stable or declining rates of psychosis between the 1960s and 1980s, while the number of people using marijuana increased dramatically. A 2003 Australian study found “no causal relationship” between cannabis use and schizophrenia, and a 2012 British study found rates of schizophrenia stable from 1950 to 2009.

Ms. Finley implies that marijuana use might be more dangerous than alcohol use. People who heavily consume alcohol risk cirrhosis, gastric and esophageal cancer, cardiomyopathy, pancreatitis and brain damage. The CDC reported 178,000 alcohol-related deaths in 2021. Marijuana doesn’t have nearly as many harmful organic effects as alcohol and has zero overdose fatalities.

We abandoned Prohibition 90 years ago and respect adults’ right to use their own judgment about the risks and benefits and safest ways to consume alcohol. It is time we treated adult marijuana use the same way.