Oral Contraceptives and Weight Gain -- April 22, 2003

Research Triangle Park, NC -- Many women stop using oral contraceptives early or never even start using them because of concerns about gaining weight. But new research reviewing 39 clinical trials of women using this effective form of birth control found no scientific proof that the pills cause an increase in weight.

Researchers performed an exhaustive search of the scientific literature to identify the trials that were reviewed. Each of the trials included weight measurements for women who were using combined oral contraceptives (those containing estrogen and progestin) for at least three cycles of treatment. A strength of the review was that it 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 between 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 lead author Maria Gallo of Family Health International, where the review was conducted. "But we did not see any substantial differences between groups taking pills or placebo or between groups taking different types of pills," she says.

Combined oral contraceptives are the most common form of contraception in the United States and are used by more than 100 million women worldwide. If taken correctly and consistently, they are more than 99 percent effective at preventing pregnancy. Under typical use, which is much more frequent, they are less effective.

Studying the association between oral contraceptives and weight gain has been difficult for multiple reasons, including the facts that many different oral contraceptive regimens exist and some women gain weight over time regardless of whether they use contraception. This review, published today in The Cochrane Library, is the first large systematic review to address the topic.

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

Researchers from Family Health International also published two other reviews today in The Cochrane Library. One examines the use of hormonal contraception by women who are breastfeeding, and the other compares the standard latex condom with an alternative nonlatex condom.

The Cochrane Library is an electronic database of the Cochrane Collaboration, 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. Family Health International contributes to the Cochrane Collaboration by producing reviews of randomized clinical trials of contraceptive methods. For more information on the Cochrane Collaboration, see http://www.cochrane.org/. To learn more about Family Health International, see http://www.fhi.org/.

Source

Gallo MF, Grimes DA, Schulz KF, et al. Combination contraceptives: effects on weight (Cochrane Review). In: The Cochrane Library, Issue 2. Oxford, UK: Update Software, 2003.

Family Health International is dedicated to improving lives, knowledge, and understanding worldwide through a highly diversified program of research, education, and services in family health and HIV/AIDS prevention and care. Since our inception in 1971, FHI has formed partnerships with national governments and local communities throughout the developing world to support lasting improvements in the health of individuals and the effectiveness of entire health care systems.