As concerns about the possible health consequences of recreational cannabis rise in U.S. states where the substance is legalized, Yale's Deepak D'Souza isn't surprised. He first noticed the negative impacts of cannabis on patients with serious mental illness when he started practicing psychiatry 30 years ago.
In 2013, while serving on the Physicians Advisory Board as Connecticut drafted its medical marijuana laws, D'Souza expressed some reservations.
"It's been clear for a while that at least in people with serious mental illness - including conditions like schizophrenia and bipolar disorder - cannabis has a negative consequence on both the expression and course of the illness," said D'Souza, the Vikram Sodhi Professor of Psychiatry at Yale School of Medicine. "People with schizophrenia who use cannabis are more likely to end up in the emergency room or hospitalized."
When Connecticut and other states began adopting policies legalizing recreational cannabis in the early 2020s, D'Souza grew increasingly concerned. It was already clear that cannabis posed risks to those previously diagnosed with serious mental illnesses. But the rub, he said, is that it can be difficult to predict who will develop such an illness in the future. Family history is an obvious risk factor, but for many young people who will develop these illnesses - and may be extra vulnerable to cannabis - there may be no known family history.
In addition to behavioral health concerns, recent reports have linked cannabis use to elevated risks of heart disease and stroke, brain developmental disorders, and spikes in emergency visits. In Massachusetts, which legalized recreational marijuana in 2016, a statewide referendum campaign to reverse the legalization policy has gained support.
A keen observer of the ongoing recreational cannabis debate, D'Souza is also director of the Yale Center for the Science of Cannabis and Cannabinoids, which studies the effects of cannabis on neurodevelopment and mental health, among other research topics.
