THERE are few more reliable routes to an early grave than cigarette smoking. But despite the dangers, nicotine addicts find it almost impossible to kick the habit. Half of those who try to stop “cold turkey” will fail within a week. Fewer than 5% manage to stay clean for a year or more. Crutches such as nicotine patches or gum, which provide the drug without the cigarettes, can help—but only a little.

One reason is that addiction is about more than mere chemistry. The rituals involved, such as holding a cigarette between the fingers or taking a long, luxuriant puff, can be as habit-forming as nicotine itself. So a better way to stop smoking might be a drug-delivery system that mimicked an ordinary cigarette as closely as possible, but had none of the pesky carcinogens and other poisons which come from burning a rolled-up mix of paper, tobacco leaves and additives.

Electronic cigarettes would seem to fit that bill. They use a small electric heater to vaporise a mix of glycerine and propylene glycol (two fairly inoffensive chemicals) in which nicotine has been dissolved, turning it into a breathable mist that can be savoured much as cigarette smoke is. And because some of these devices are designed to resemble traditional cigarettes, they can be held between the fingers and jabbed in the air for emphasis, just like the real thing.

However, the novelty of e-cigarettes (the first of which hit the market in 2006) means there is only a smattering of evidence addressing the question of whether they actually do help smokers ditch the real thing. On December 17th, though, more evidence arrived—in the form of a review published by the Cochrane Collaboration, an international medical research organisation. The review’s authors, led by Peter Hajek of Queen Mary, a college of the University of London, examined results from 13 trials of e-cigarettes. The results, though a long way from being definitive, are encouraging.

Two of the studies the team looked at were randomised control trials. These are the highest form of medical evidence, in which doctors assign volunteers at random to the treatment being studied or to something else, and compare the results. In the cases examined, the something else was a placebo e-cigarette. This resembled the real thing, but delivered no nicotine. About 9% of people using electronic cigarettes in these studies managed to abstain from smoking for six months, as against 4% of those using the placebos. One of the studies also found that e-cigarettes were at least as useful as nicotine patches in encouraging abstinence (the other did not examine this question).

Giving up smoking is the ideal outcome, but puffing less is good for you as well. Both studies suggested that e-cigarettes help those who cannot face giving up completely to cut their consumption significantly. Some 27% of smokers using placebo e-cigarettes, and 36% of those using the genuine electronic article, were able to do so by half or more. One of the trials also compared e-cigarettes with nicotine patches. In that study, 61% of e-cigarette users were able to cut their consumption by half, compared with only 44% of those using patches. These general conclusions were supported by the 11 remaining investigations, known as cohort studies, in which doctors merely monitored people for a time, without attempting to influence their behaviour.

And now for the health warnings

There are, inevitably, caveats. Dr Hajek’s review includes only a small number of studies, each of which involved what was, by the standards of such trials, a small number of people. (Because successfully quitting smoking is a rare event, statisticians need to follow a lot of people to extract a clear signal.) People claiming to have quit were given biochemical tests to make sure they were telling the truth, but those who claimed merely to have cut back on their intake had to be taken at their word. In general, Dr Hajek and his team rated the quality of the evidence as either “low” or “very low”. And the two clinical trials used now-obsolete forms of e-cigarette that do not pack as much of a nicotinic punch as that delivered by more modern varieties.

Moreover, unlike conventional cigarettes, which are made by the zillion by big tobacco companies, using standardised industrial processes, e-cigarettes are manufactured by hundreds of firms of varying sizes, most of which are located in China. Their quality is therefore variable. Some have been found to have heavy metals from the heating element in the supposedly clean nicotine mist. Others have fibres of silica, which could irritate users’ lungs, in the vapour.

Such things will, no doubt, change as more reputable firms displace the less reputable. And more data on the effectiveness of e-cigarettes are now being collected. The study’s authors have identified nine trials now under way. If these, too, come back positive, then grounds for scepticism will be much diminished.