HOLLYWOOD seldom depicts junkies in suits and ties. But in recent weeks several public figures have admitted taking hard drugs while working in high-powered jobs. Toronto’s serially scandalous mayor, Rob Ford, has admitted that he smoked crack cocaine two years ago, while in office. Trey Radel, a Florida congressman, is under pressure to resign after being convicted of possessing powder cocaine. In Britain Paul Flowers, a former chairman of the Co-op bank (and a Methodist preacher to boot) was arrested after a newspaper filmed him apparently buying methamphetamine and other drugs. If people can take hard drugs and still go on running a national bank or Canada’s biggest city, how dangerous can such substances be? One way of judging a drug’s harmfulness might be to see how it is treated in the courts. But the drug laws are frequently eccentric. Until recently in America an automatic five-year jail sentence was mandated by the possession of just five grams of crack cocaine, while it took at least 500 grams of powder cocaine to trigger the same penalty. (The Fair Sentencing Act of 2010 reduced the disparity from 100:1 to 18:1.) In Britain, the government classifies drugs’ harmfulness on a scale from A to C. But ministers' tendency to use the system to send warning messages to the public means that popular drugs are sometimes given higher ratings than they might deserve. Cannabis, which has been smoked by nearly one in three British adults, is officially deemed more dangerous than GHB, a “date rape” drug that can kill. Even the sanest legal systems cannot keep up with the stream of potentially harmful “legal highs” that are too new to have been classified at all.

Researchers have sometimes tried to compare drugs' harmfulness on a more scientific basis. Perhaps the best-known recent ranking was led by Professor David Nutt, a former chief drugs adviser to the British government, and published in the Lancet in 2010 (we reproduced a simplified version of its results here). Its conclusion was that alcohol was more harmful than any banned drug—which might seem odd, given that Mr Radel cited his alcohol abuse as the reason for his (implicitly far worse) cocaine habit. But to reach this conclusion the study factored in the harm done not just to the user, but to society. If one looks only at the risk to the user then banned drugs are indeed somewhat more harmful than alcohol. In the Lancet study crack, heroin and methamphetamine were all judged to do more harm to the user than alcohol (powder cocaine was not). The direct risk of death, which often grabs headlines, was reckoned to be highest under heroin and its cousin methadone. Crack and crystal meth contributed most to the “impairment of mental functioning”.

So is it better to have a politician who is an alcoholic or a drug addict? An alcoholic is a bit more likely than a crack-smoker to die, but the crack-smoker is more likely to have his judgment fuddled. Drinkers are also slightly less likely to slip into dependency; crack, heroin and meth are more moreish than alcohol (though no more so than tobacco). Drug-using public figures may also have more trouble maintaining the trust of voters. For one thing, taking drugs implies breaking laws, an undesirable characteristic in those who write them. There is also evidence that users of certain illegal drugs are slightly more likely to experience breakdowns in personal relationships than those who abuse alcohol. Professor Nutt and his colleagues found that on this score, meth and crack were the most damaging substances. That seems to have been borne out by Mr Flowers, the “crystal Methodist”, who has been disowned by many former allies and whose appointment to the Co-op is to be the subject of an inquiry. Mr Ford, by contrast, is doing his best to prove the researchers wrong. Still in his post, he has promised to run for re-election next year. One recent poll suggested that his approval rating had not been affected much by the scandal. Indeed, one-third of Torontonians intend to vote for him again.