Almost everything you think you know about the health effects of cannabis, almost everything advocates and the media have told you for a generation, is wrong.

Seventy miles northwest of New York City is a hospital that looks like a prison, its drab brick buildings wrapped in layers of fencing and barbed wire. This grim facility is called the Mid-Hudson Forensic Psychiatric Institute. It’s one of three places the state of New York sends the criminally mentally ill—defendants judged not guilty by reason of insanity. Until recently, my wife Jackie­—Dr. Jacqueline Berenson—was a senior psychiatrist there. Many of Mid-Hudson’s 300 patients are killers and arsonists. At least one is a cannibal. Most have been diagnosed with psychotic disorders like schizophrenia that provoked them to violence against family members or strangers. A couple of years ago, Jackie was telling me about a patient. In passing, she said something like, Of course he’d been smoking pot his whole life. Of course? I said. Yes, they all smoke. So marijuana causes schizophrenia? I was surprised, to say the least.

Jackie would have been within her rights to say, I know what I’m talking about, unlike you. Instead she offered something neutral like, I think that’s what the big studies say. You should read them. So I did. The big studies, the little ones, and all the rest. I read everything I could find. I talked to every psychiatrist and brain scientist who would talk to me. And I soon realized that in all my years as a journalist I had never seen a story where the gap between insider and outsider knowledge was so great, or the stakes so high. I began to wonder why—with the stocks of cannabis companies soaring and politicians promoting legalization as a low-risk way to raise tax revenue and reduce crime—I had never heard the truth about marijuana, mental illness, and violence.

More From Hillsdale - Imprimus: