A Swedish thesis has trashed the commonplace notion that combined oral contraceptive pills (COCPs) cause weight gain, suggesting that birth control pills containing oestrogen and progesterone derivatives are a safe bet for women who don’t want to suffer from an unwanted side effect like obesity when on the pill.

1,749 Swedish women – born in a decade apart from 1962 to 1982 – were quizzed on contraception use, pregnancy, smoking habits and height-to-weight ratios by researchers from the Sahlgrenska Academy of University of Gothenburg.

On completion of the observation period, the researchers found that those on the pill for the long term did not gain more weight than those who never used oral contraception.

Study co-author Ingela Lindh said the combined oral contraceptive pill was found to be the most common method of birth control in women aged 29 or below and was then replaced with barrier methods such as condoms or intra-uterine devices.

Use of oral contraception and weight gain are unrelated, the study authors noted, adding that those who did pile on the pounds had other obesity risk factors, including smoking and age-induced obesity. It would be wrong not to use the pill for fear of becoming overweight or obese, assured Ms Lindh.