The Politics of Schizophrenia

“There is now sufficient evidence to warn young people that using cannabis could increase their risk of developing a psychotic illness later in life,” according to a paper in The Lancet July 28.

The “evidence” was produced by an exercise in statistics. The authors (no MDS among them) searched databases for relevant studies and then analyzed 35 of they deemed worthy. They claim to have “adjusted for about 60 different confounding factors, including other substance use, personality traits, socio-demographic markers, intellectual ability and other mental health problems.” They concluded that people who have used cannabis face a 40% higher risk of psychosis, and that heavy use increases the risk to 50-200%.

The British government has been reconsidering the legal status of cannabis, which in 2004 was moved from Class B to Class C -a less dangerous drug category with less onerous penalties for growers, distributors and users. Prohibitionist forces -notably the big drug companies and law enforcement- protested. In 2005 the Advisory Council on the Misuse of Drugs reviewed the medical literature, held hearings and concluded that Class C indeed was the appropriate category. The Council’s report stated “for individuals, the current evidence suggests, at worst, that using cannabis increases the lifetime risk of developing schizophrenia by 1%.” The latest Lancet paper is being played as a trump card to that report:

“Smoking Just One Cannabis Joint Raises Danger of Mental Illness by 40%” -Daily Telegraph.

“Cannabis ‘Doubles Risk of Psychotic Illness'” -The Times

“Weed May Make You Go Psycho” -Daily Mail.

The Independent on Sunday, the most zealous advocate of returning cannabis to Class B, supplemented its summary of the Lancet paper with a survey headed “50 Top Experts Confirm Mental Health Risk Their poll does not and literally could not “confirm” the risk posed by cannabis, it can only “confirm that most believe…” As the story explains: “A poll of more than 50 of the world’s leading authorities on drugs and mental health, confirms that most believe cannabis, and particularly its stronger variant, skunk, pose significant health risks and increase users’ susceptibility to psychosis and schizophrenia.”

We sought a 51st opinion from Lester Grinspoon, MD, professor of psychiatry emeritus at Harvard who has been studying marijuana since 1967 and is the co-author of Schizophrenia: Pharmacotherapy and Psychotherapy and other textbooks. “It is hard to refute a study that alleges certain things are going to happen in the years ahead,” he says, “but smoking marijuana does not cause schizophrenia.”

Grinspoon and the psychiatric establishment agree that schizophrenia is caused by a damaged gene or an insult in the womb or infancy that results, when the brain develops and gets exposed to hormones produced in adulthood, in an organic malfunction. There ensues a break with reality, sometimes accompanied by visual hallucinations or “voices.” Very often the break has an apparent “precipitating event,” says Grinspoon, “-a serious automobile accident, loss of a loved one, an alcoholic binge a bad reaction to LSD or even, I imagine, to marijuana. But it’s important to distinguish between ‘precipitating event’ and ’cause.'”

Can those teenagers at risk for schizophrenia be warned that cannabis should be avoided? Grinspoon responded,”We have no way of identifying a pre-schizophrenic individual.” He recalled a study in which psychiatrists were shown home movies of young children, some of whom became schizophrenic in early adulthood. The specialists could identify the pre-schizophrenic children “in most cases,” said Grinspoon, but the warning signs were subtle and the study led to no practical application. Anecdotal evidence suggests that people heading for a schizophrenia diagnosis are often very original thinkers.

U.S. researchers have found that schizophrenics use cannabis at about twice the rate of the general population, and alcohol and nicotine at similarly high rates. Often these drugs are combined. Whether cannabis use exacerbates or quells symptoms of psychosis is at the heart of the centuries-old debate. People use cannabis for various reasons and have varying responses. Levels of anandamide -“the brain’s own marijuana,” as Scientific American put it- are higher in the brains of schizophrenics, but again it’s unclear whether this is in response to a problem or the cause of the problem.

The Lancet paper is “a meta-analysis of studies that are themselves flawed,” says Grinspoon (who discredited some of them himself). “It greatly exaggerates the risk to the individual.” The cannabis-causes-psychosis line is disproved, according to Grinspoon, by the absence of “even a blip in the incidence of schizophrenia in the US after millions of people started smoking marijuana in the 1960s.” The incidence of schizophrenia in adults is about 1% worldwide and seemingly independent of whether or not cannabis use is widespread in a given culture.

In a meta-analysis published in the Lancet in 2004, John Macleod and co-authors pointed out, “Cannabis use appears to have increased substantially amongst young people over the past 30 years, from around 10% reporting ever use in 1959-70, to around 50% reporting ever use in 2001 in Britain and Sweden. If the relation between use and schizophrenia were truly causal and if the relative risk was around five-fold, then the incidence of schizophrenia should have more than doubled since 1970. However, population trends in schizophrenia incidence suggest that incidence has either been stable or slightly decreased over the relevant time period.”

This sweeping, common-sense refutation of a causal link can only be gotten around by defining currently available cannabis as a new and different drug -which is what the prohibitionists are doing with their “skunk” appellation. But the increase in THC content is not a sudden phenomenon, it has occurred over the course of decades (documented in the U.S. by DEA analysis of confiscated cannabis), and the incidence of schizophrenia has not risen correspondingly. Nor has the widespread use of Marinol -synthetic THC, available by prescription in the U.S. since 1986- resulted in a higher incidence of schizophrenia.

Unmentioned in the media response to the recent Lancet paper is the fact that Prohibition has prevented growers from developing cannabis strains high in cannabidiol (CBD), a component of the plant that counters the anxiety- and confusion-producing effect that THC exerts on some people.

Some Unambiguous Dangers of Cannabis

According to Dr. John Macleod, lead author of the Lancet’s 2004 meta-analysis,

“It is unfortunate that the debate around whether cannabis causes schizophrenia has become conflated with the debate around the legal status of cannabis, and that this question has come to dominate discussions around the appropriate public-health response. The public-health case for prevention of cannabis use by young people is strong, irrespective of whether use also causes schizophrenia.”

And what is “the public-health case” against young people using cannabis? “Most users seem to smoke cannabis with tobacco,” writes Macleod. “Cannabis use can actually lead to initiation of tobacco use, reinforce toxic effects of tobacco, and make abstinence from tobacco more difficult. Moreover, in most jurisdictions, cannabis use exposes young people to risks of criminalisation that could have additional consequences for their health.”

Classification of Drugs in the UK

Class A (most harmful) includes cocaine, heroin, ecstasy and LSD. Class B (intermediate) includes amphetamines, barbiturates and codeine. Class C (least harmful) includes cannabis, benzodiazepines, anabolic steroids, and GHB.

FRED GARDNER edits O’Shaughnessy’s, the journal of cannabis in clinical practice. He can be reached at


Fred Gardner is the managing editor of O’Shaughnessy’s. He can be reached at