No evidence OCs cause weight gain.

There is no evidence that oral contraceptives (OCs) cause weight gain, according to an FHI-conducted review of 39 clinical trials of women using this effective method of family planning. The review, published in late April 2003 in the Cochrane Library, was the first large systematic review to address the topic.

Each of the 39 trials included weight measurements for women who were using combined OCs (those containing estrogen and progestin) for at least three menstrual cycles. The review was limited to randomized controlled trials, the "gold standard" of trial designs for reducing the potential for bias. Two of the trials compared weight changes in women taking oral contraceptives versus weight changes in women taking placebos. Neither trial showed an association between oral contraceptives and weight gain. The remaining trials compared weight changes among women taking different oral contraceptive regimens. While some women gained weight and some lost weight over time, overall differences between groups were minimal. The largest difference in weight change between groups was less than five pounds.

"It is interesting to compare different combination contraceptives, because if the estrogen or the progestin in the pills or the type of pill is causing weight gain, then you would expect differences between groups," says Maria Gallo, an FHI research associate and lead author of the review. "But we did not see any substantial differences between groups taking pills or placebo or between groups taking different types of pills," she says.

"It is very reassuring news," says coauthor Dr. David Grimes, FHI vice president of biomedical affairs. "A widely held myth suggests that oral contraceptives cause weight gain, but the answer as best we can tell is they do not."

Recognizing that some women may still perceive a gain in weight while using OCs, providers may want to explain to clients that the studies do not rule out a small increase in weight among some women. "Counseling should be tailored and flexible," says Dr. James D. Shelton, senior medical scientist at the U.S. Agency for International Development (USAID). "Providers might say, for example, 'On average, pills do not cause weight gain. However, as an individual, you might experience some modest weight gain or loss. Would that be important to you?'"

The Cochrane Library, where the review was published, is an electronic database of the Cochrane Collaboration (http://www.conhrane.org), an international organization committed to helping people make informed health care decisions by preparing, maintaining, and promoting systematic reviews of the effects of health care interventions. FHI contributes to the Cochrane Collaboration by producing reviews of randomized clinical trials of contraceptive methods.