Birth Control Pills Do Not Lead to Major Weight Gain

Despite a common belief that birth control pills cause weight gain, a new comprehensive review of previous studies finds no evidence it is true.

"There's evidence that women may switch methods of birth control or stop using the pill because they think it contributes to weight gain," said Laureen Lopez, Ph.D., a review co-author. "The good news is that this review found no evidence to support a causal association between combination contraceptives and weight gain."

Birth control pills containing two hormones (estrogen and progestin) are the most well-known form of combination contraceptives; however, women can also be given combination contraceptives by other methods such as skin patches or injections.

Lopez, of the nonprofit organization Family Health International, and colleagues analyzed data from 44 randomized controlled trials that compared a combination hormonal contraceptive to a placebo or to another hormonal contraceptive. All studies included information on change in body weight. While the evidence was not strong enough to rule out the possibility of weight gain with combination hormonal contraceptives, it did not find a major effect.

The review appears in the current issue of The Cochrane Library, a publication of the Cochrane Collaboration, an international nonprofit organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Only three of the 44 studies compared a hormonal contraceptive to an inactive placebo. Two were trials of contraceptive pills, while one used a skin patch. None of these three studies showed a significant increase in weight in women using the contraceptive compared to those using the placebo.

For the 41 head-to-head studies that compared different hormonal contraceptives or different doses or regimens, most comparisons did not show substantial differences in weight.

"Weight gain is a major problem in the U.S.," said Lopez. "Over time, many people do put on weight, and some women's perception about weight gain may be that it's because of the pill."

Fear of weight gain is one of the most common reasons that women don't use - or discontinue use of - the pill. In a national survey of American women ages 18 to 45, published in 2000 in the International Journal of Gynecology and Obstetrics, half believed that oral contraceptives cause weight gain, and one in five women claimed that fear of gaining weight was a reason they would not start or would discontinue the pill.

"The myth that the pill causes weight gain is deeply entrenched," said Carolyn Westhoff, M.D., professor of obstetrics and gynecology at Columbia University, "and the most weight-obsessed segment of the female population just won't take hormonal contraception at all because they think they're going to gain weight."