Is Cannabis-Linked Schizophrenia on the Rise?

A new study out of Denmark has found an increase in schizophrenia cases linked to excessive marijuana use. The findings were published in JAMA Psychiatry and could carry significant implications for drug and mental health policy.

The proportion of schizophrenia cases linked to marijuana increased 3 to 4 times over the last two decades, the researchers found. Cases rose from around 2% in the period to 1995 to approximately 6% to 8% since 2010.

In addition to cannabis’ growing popularity, increased potency was hypothesized as a factor.

“Cannabis use disorder is not responsible for most schizophrenia cases, but it is responsible for a nonnegligible and increasing proportion,” wrote J. VanderWeele, a professor in the Departments of Epidemiology and Biostatistics at the Harvard T. H. Chan School of Public Health. “This should be considered in discussions regarding legalization and regulation of the use of cannabis.”

Schizophrenia is a long-term psychiatric disorder characterized by disordered patterns of thought, hallucinations and/or delusions, and behavior that interferes with daily life. Onset typically occurs in early adulthood.