The Marshall Project: This first question is for all of you. Let’s start with the core question Alex set out to answer in reporting his book: What do we know about the connection between marijuana and mental illness? What would you say is established medical science, and what is still unresolved?
Alex Berenson: Okay, I’ll jump in. Marijuana causes psychosis. This is an established medical fact, not open to debate. It can cause temporary psychotic episodes even in healthy people. It worsens the course of schizophrenia and provokes severe relapses in people with schizophrenia whose disorder was controlled.
The mainstream literature and the physician-scientists who have done the most work on the issue also believe it is responsible for some cases of schizophrenia that otherwise would not have occurred—that is to say, that it can cause schizophrenia, especially when used regularly to heavily by adolescents. The advocacy community focuses on that part of the issue and overstates the uncertainties surrounding it, which after 30 years of research are relatively minor, and probably relate more to risk ratios than anything else. But in doing so, advocates elide an equally significant issue. Even if marijuana did not produce a single de novo case of schizophrenia, its use frequently causes temporary episodes of psychosis. To say otherwise is to ignore the reality of emergency rooms all over the United States.
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What research does indicate is that some people with certain genetic markers for schizophrenia and other psychiatric disorders may be more likely to use marijuana and other drugs. There is also research to suggest that individuals with certain markers may be more likely to experience psychosis or develop psychiatric disorders, including schizophrenia, due to substance use.
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