You may have seen recent headlines proclaiming that just one joint ever was enough to increase your risk of becoming schizophrenic by 40%. While we just tend to accept that most newspaper reports on drugs—their use and their effects—are inaccurate to the point of propaganda, it is sometimes good to get the figures behind the story. Ben Goldacre of the Guardian over at his Bad Science blog has the truth:
It was also interesting to see how the risk was numerically reported. The most dramatic figure is always the "relative risk increase", or rather: "cannabis doubles the risk of psychosis", "cannabis increases the risk by 40%". Because schizophrenia is comparatively rare, translated this into real numbers this works out - if the figures in the paper are correct, and causality is accepted - that about 800 yearly cases of schizophrenia are attributable to cannabis. This is not belittling the risk, merely expressing it clearly.
In turn, of course, this is linked to the Government wanting to re-re-classify pot. There are, no doubt, some very solid reasons for doing this, but in the absence of reason it seems scare-mongering might just work instead. Goldacre skewers this too:
And craziest of all is the fantasy that reclassifying cannabis will stop six million people smoking it, and so eradicate those 800 extra cases of psychosis. If anything, for all drugs, increased prohibition may create market conditions where more concentrated and dangerous forms are more commercially viable. We’re talking about communities, and markets, with people in them, after all: not molecules and neuroreceptors.