STATS ARTICLES 2006

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Guardian Goes Potty Over Cannabis-Schizophrenia Link

February 20 2006
Maia Szalavitz
Guardian/Observer report takes its cues from U.S. drug czar not science

The quality British press doesn’t usually go in for American-style drug hysteria, but this article from last week’s Guardian/Observer could have been mistaken for a press release from the U.S. drug czar. It contained accounts of violent crimes committed by cannabis users and an essay by a thirteen-year-old about why she hates her brother who is “currently ill with squitsaphrenia [sic] due to taking drugs (cannabis) from an early age.”

The misinformation begins with the sub-head, which claims that “a series of new studies proves the link between cannabis dependency and mental illness,” implying that marijuana causes mental illness. In fact, the new research, like the previous data, does not prove that marijuana makes people mentally ill, but merely finds that people who are mentally ill are more likely to smoke pot.

The article also mischaracterizes a recent report by the British government’s Advisory Council on the Misuse of Drugs. The UK recently “reclassified” cannabis possession as an offense so minor that users cannot be arrested simply for having small quantities in their possession. The ACMD was recently asked to determine whether the government should reconsider that decision, in light of a possible link between marijuana and mental illness.

The Guardian/Observer piece described the ACMD report as having argued “against reclassification,” and claimed that it “suggested for the first time that cannabis may not only cause schizophrenia in those with pre-existing mental conditions, but could also exacerbate a range of other mental health problems.”

The ACMD report actually said that marijuana should remain reclassified as a non-arrestable offense and here are some of its key points:

The high prevalence of cannabis use, as well as use of other controlled substances, among those with schizophrenia or psychotic disorders is not understood. It may be cultural or related to peer pressure; and it has been postulated that cannabis either helps deal with certain aspects of the condition, or that it even ameliorates some of the adverse consequences of medication …

Over the past few years, there has been growing concern as to whether cannabis use might precipitate chronic, or enduring, psychotic illnesses, including schizophrenia. In view of the ability of cannabis to precipitate relapse in individuals with established schizophrenia…it is clearly a biologically plausible hypothesis. However, research in this area is fraught with problems of both study design and interpretation.

…For individuals, the current evidence suggests, at worst, that using cannabis increases the lifetime risk of developing schizophrenia by 1%.

…The most recent data are not, overall, persuasive of a causal association between cannabis use and the development of depression, bipolar disorder or anxiety.

The Guardian/Observer claims that marijuana-related admissions to hospital for mental illness in the UK have almost doubled in recent years, citing 490 such admissions in 2001, compared to 710 in 2004 and the same number in 2005. But what it doesn’t cite is a source for those numbers, nor does it say how a “cannabis-related” hospital admission is defined.

When doctors go looking for an association, one is often found — so it’s quite possible that admissions that previously would not have been classified as “cannabis related” are now being linked with the drug.

Also, annual marijuana use rates by teenagers and young adults actually fell in the UK during that period — from 28% in 1998 to under 24% in 2005, a fact unmentioned by the newspaper. Nor is there evidence that marijuana potency suddenly skyrocketed in the 00’s. Claims about super-strong pot go back much further.

Finally, the article doesn’t mention the most compelling evidence against a causal link between marijuana and schizophrenia. Schizophrenia rates have been stable around the world at roughly 1% of the population for as long as they have been measured. Marijuana use rose in the West from virtually zero in the early 20th century to 50-60% of the adult population having tried it at least once in recent decades, with substantial proportions of the population taking it regularly at some point in their lives, often during adolescence. Schizophrenia rates haven’t budged.