Overweight people often dream about a magic bullet that will make them slim overnight. But dexfenfluramine is one bullet that can be hit or miss, sometimes with serious consequences.

Controversially, it has finally won Food and Drug Administration (FDA) approval to be marketed in America from this summer. Dexfenfluramine is a serotonin reuptake inhibitor which makes the patient feel sated. It's available in the US as Redux, marketed by Wyeth Ayerst, and in Britain as Adifax, marketed by Servier.

Not for the first time, the US drug regulators have been far more rigorous than their European counterparts. Its first application was refused by the FDA advisory committee, while the pressure group, Public Citizen's Health Research Group, maintains its risks outweigh any benefits.

The Group says that those on the drug for more than three months are nine times more likely to have primary hypertension of the lung. It also warns that the drug may not be very effective; studies have shown that patients have lost no more than 3.4 kg (about 8 lbs) more than those on placebo, it maintains. The Group advises patients to come off the drug after three months if they have not lost weight in that time, a recommendation that is also voiced by some European regulators.

Common side effects include dry mouth, nausea, constipation, drowsiness, dizziness, headache, mood disturbance, depression, insomnia, nervousness and conjunctivitis.

There's been at least one fatal case of pulmonary hypertension during long term use of dexfenfluramine, although a direct link with the drug hasn't been established.

A study in 1994 involving animals showed that the drug can lead to persistent and permanent brain damage.

Oh well, there's always dieting, we suppose.