The medicalisation of obesity goes ahead at full tilt. Increasingly, fat people are not seen as self-indulgent or slothful but as victims of an "obesogenic environment", incapable of taking their fate in their own hands and prime candidates for medication.

Indeed, even to suggest that this is a matter for individual decision, and not for national hand-wringing, is to step over an invisible line. Overweight people are victims and to imply that they have brought their problems on themselves is to deny their victimhood.

So turning obesity into a medical problem suits everybody: the Government because it has decided that obesity is a problem but has no idea how to deal with it; obese people because they can console themselves that they have a disease; and the drug companies, which see a pot of gold in developing anti-obesity drugs and vaccines.

Acomplia, a drug that reduces weight by acting on the appetite pathway, got a rapturous reception in June when it won a licence from the European drug regulatory agency. This week a team from California reported success with an obesity vaccine. Scientists from the Scripps Research Institute, in La Jolla, reported that when they gave rats a vaccine against a hunger hormone called ghrelin, the animals were able to eat what they wanted without putting on fat.

If this vaccine ever becomes a reality for human beings, it will be aimed at "yo-yo" dieters whose weight oscillates wildly. What gives the vaccine its unique selling proposition, however, is that it appears to affect the rats' metabolism, not just their appetite. Fat people often claim — possibly with some justification — that their metabolism is different from leaner folk. A vaccine that could put that right would have the punters clamouring.

But changing people's metabolism, or messing with their hormones, is not a trivial matter. Drugs that are to be used by healthy people, such as the Pill and HRT, have to meet far more stringent safety requirements than those intended for the ill.

So the medicalisation of obesity matters because if the overweight are defined as ill, it lowers the threshold of safety that a drug has to meet. And there are dangers in that, as another of this week's stories pointed out.

Acomplia is a close relation of the cannabinoids, the active ingredients in marijuana. But while hash can give users the "munchies" — a powerful desire for food — Acomplia is designed to do the opposite. Both work by affecting a chemical called anandamide, which has effects both in the brain and in other organs as well.

A study of the effects of marijuana, this time among mice, showed that it can disturb the anandamide balance and cause a lot of complications in pregnancy, including ectopic pregnancies, when the foetus is implanted in the wrong place.

The research did not show that the same was true for Acomplia but it suggested it might be. No drug that has yet been invented has effects but no side-effects, so we must be especially careful that the anti-obesity drugs really do more good than harm.

But surely the benefits of cutting weight will outweigh any small side-effects? Maybe, but actually the health benefits of being thin are not quite as clear-cut as everybody believes. Being fit is more important than not being fat, as an abundance of evidence has shown.

Among the middle-aged, those who live longest are those who are a little overweight but not obese.

So we should beware of the obesity panic driving us into medical solutions until we are really sure that the cure is safe.

Ten years ago, the hugely popular slimming drug Fen-phen was removed from the US market after it was found to have caused heart problems. It would be careless to make the same mistake again.