Objectives: To study how often women put on weight when on the pill and to analyse the relationship between that gain in weight and the characteristics of the last 2 types of pill that had been used.

Patients and methods: Three thousand six hundred and nine women representative of the French female population, aged 15 to 45, were recruited thanks to a survey that took place in 2001. Our study mainly concerned the 1665 women who were actually taking the pill at the time of the survey. The data were collected from self-questionnaires.

Results: Thirty per cent of women declared to have gained weight since using their latest pill - only one more kg for 4% of them, 2 kg for 10% but 3 kg or more for the remaining 16%. Gain in weight was more frequent with women less than 25 years of age (35%) than with older ones (29%). This gain in weight did not vary according to either the type of pill, which was then used, or the length of time spent in using it, or the age of first using. It was more frequent when found with other side effects such as breast pain, skin disorders or metrorrhaegias; it was less frequent among women who had already been on the pill in the past than among women using an oral contraceptive for the first time (28% vs 34%; P = 0.008). The shorter the taking the latest pill had been, the greater the frequency of gain in weight was (P = 0.005), women who had presented the most side-effects in the past having changed their pill more rapidly than other women. Finally, a gain in weight was found far more often in women who "did" put on weight with their latest pill than in those who "did not" (53% vs 14%; P = 0.0001). All in all, 8% of women who had been previously been taking the pill had given up this method over a weight problem.

Discussion and conclusion: Putting on weight when on the pill being in the long term independent of the type of patent medicine used, it would seem necessary to orientate new research centred both on a chemical and a biological as well as a nutritional approach, so as to answer one of the major preoccupations of oral contraceptive users to the fullest.