The bogus claim:
A single joint of cannabis raises the risk of schizophrenia by more than 40 per cent, a disturbing study warns. The Government-commissioned report has also found that taking the drug regularly more than doubles the risk of serious mental illness. Overall, cannabis could be to blame for one in seven cases of schizophrenia and other life-shattering mental illness, the Lancet reports. The grim statistics – the latest to link teenage cannabis use with mental illness in later life – come only days after Gordon Brown ordered a review of the decision to downgrade cannabis to class C, the least serious category.
Talk about politicizing science. You think it’s a coincidence the study comes out right when the UK government’s evaluating re-scheduling the drug for stiff new penalties? Similar studies have been published in the Lancet many times over the years. But where are all the schizophrenics? And why is now the time for such wildly sensationalized banner headlines?
The only way I can interpret the Lancet study is that the small natural statistical risk of schizophrenia (about 1 in 120) may rise 40% to about 1 in 86. but the article seems to contradict this:
‘While the majority can take the drug with no mind-altering effects, it is estimated that 10 per cent are at risk.
So which is it: a 40% increase across the board, or a 40% increase among the 10 percent at risk? The journalists who wrote the article didn’t clarify what they meant. There’s a big difference between saying “everyone is at risk,” and certain people with certain predispositions are at risk.
Pot is America’s (and likely also the UK’s) top cash crop (previous post), which translates into tens of millions of pot smokers. If the 40% increase in risk were true for “one joint”, we should have at least 266,667 additional schizophrenics (out of 80 million people who’ve tried at least one joint). According to the NORML FAQ:
Marijuana is the third most popular recreational drug in America (behind only alcohol and tobacco), and has been used by nearly 80 million Americans. According to government surveys, some 20 million Americans have smoked marijuana in the past year, and more than 11 million do so regularly despite harsh laws against its use.
In addition, any such study would have to control for all other risk factors, genetic and environmental, for mental illness. Without far more precise tools of genetic analysis, we can’t make such a judgment. And since the study claims lifelong risk, it would have to have been conducted over many decades.
Clearly, the vast majority of pot-smokers view the effects of cannabis to be positive enough to warrant taking that risk. Especially medical marijuana users who may have other even greater risk factors, (such as loss of vision for glaucoma patients, or debilitating nausea), if they don’t smoke.
Either way, life cannot be made completely safe. Every decision we make is a risk-reward calculus. Here’s another statistic: A person has about a 1 in 84 chance over the course of a lifetime of being killed in a car accident. But who would argue on that basis that we should all stop driving?
UPDATE: Yahoo has a much better article on the study, indicating the increased risk is inconclusive, and almost certainly much lower than 40%.
The researchers said they couldn’t prove that marijuana use itself increases the risk of psychosis [emphasis added], a category of several disorders with schizophrenia being the most commonly known.
There could be something else about marijuana users, “like their tendency to use other drugs or certain personality traits, that could be causing the psychoses,” Zammit said.
Zammit and colleagues from the University of Bristol, Imperial College and Cambridge University examined 35 studies that tracked tens of thousands of people for periods ranging from one year to 27 years to examine the effect of marijuana on mental health.
They looked for psychotic illnesses as well as cognitive disorders including delusions and hallucinations, bipolar disorder, depression, anxiety, neuroses and suicidal tendencies.
They found that people who used marijuana had roughly a 40 percent higher chance of developing a psychotic disorder later in life. The overall risk remains very low [emphasis added].
For example, Zammit said the risk of developing schizophrenia for most people is less than 1 percent. The prevalence of schizophrenia is believed to be about five in 1,000 people. But because of the drug’s wide popularity, the researchers estimate that about 800 new cases of psychosis could be prevented by reducing marijuana use [emphasis added–reducing driving could reduce fatal auto accidents as well].
The scientists found a more disturbing outlook for “heavy users” of pot, those who used it daily or weekly: Their risk for psychosis jumped to a range of 50 percent to 200 percent.