By Mitch Earleywine, Ph.D.

The Office of National Drug Control Policy now asserts that teens who smoke pot increase their risk of mental illness—a claim based largely on misinterpretations of scientific studies, most recently one published in late 2005 in the British Journal of Psychiatry and another presented at last year’s annual meeting of the Radiological Society of North America. By the time the Drug Czar’s message was dutifully amplified in the media, it had become “Marijuana causes schizophrenia.” Soon enough, the Independent newspaper in the UK was reporting that British Prime Minister Tony Blair now plans to use the alleged link as cover for a move to roll back British cannabis-law reform, returning marijuana to a more restrictive Class B status after more than two years in Class C.

Schizophrenia is no joke. Its delusions and hallucinations affect only about 1 percent of the world, but those few have a rough time. I lived with 10 schizophrenics in a halfway house for a couple of years—not so much because I’m crazy, but to pay the rent in graduate school—and these weren’t the mildly quirky mentally ill stereotyped on sitcoms as witty and wise. I had one housemate ask me if the people on TV could see him; another believed that an elite commando group was planning his assassination. If marijuana actually was behind this, we really would need to do something. I only wish schizophrenia were that easy to fix.

Worries about marijuana and mental illness date back at least to the year 200, when Asian physicians warned that large doses could lead to seeing demons. In the 1840s, the French physician Dr. Jacques-Joseph Moreau, who had supplied the legendary European artists of the Hashish Club with their monthly doses, suggested that marijuana intoxication paralleled mental illness. In 1936, Reefer Madness reflected the popular wisdom that the plant caused users to become “criminally insane.” The cult-classic movie shows pot leading to paranoia and violence, as well as an absurd desire to hear piano music played faster and faster.

In 1944, legitimate researchers tried to come to the rescue. They never wanted to free the weed, but they did want to understand the mentally ill, and their findings appeared in the LaGuardia report, prepared by the New York Academy of Medicine at the behest of Fiorella LaGuardia, the then mayor of New York (now best known for the airport named in his honor). The LaGuardia Commission concluded that a few folks with already-existing psychotic disorders were bound to have a bad reaction to marijuana, but that the herb made everyone else happy and relaxed. A report issued during the Johnson administration said essentially the same thing. And then another during Nixon’s presidency confirmed the results.

But whatever’s old is new again.