Some women think that birth control pills make them fat. Some may avoid them because of that belief. In fact, for most women, hormonal contraceptives have little influence on their weight. This includes pills, birth control patches, vaginal rings, birth control implants, and birth control injections
Weight gain is listed as a possible side effect on the packages of some hormonal contraceptives. But weight loss is also listed. So what is going on here?
Some women do report gaining weight. Others report losing weight. That helps explain why both possibilities are listed. Research on groups of women have had mixed results.
When collected together, decades of studies have failed to show a definite association of any hormonal method with weight gain1,2.
- Researchers from the Cochrane Collaboration looked at 49 studies comparing different types of combination hormonal contraception. They found that “evidence was insufficient to determine the effect of combination contraceptives on weight, but no large effect was evident.” In other words, if there were a strong effect on weight, it would have been noticeable across these studies1.
- In a separate review, the Cochrane Collaboration looked at 22 studies examining progestin-only contraception and weight gain.
- They found no high-quality evidence that progestin-only users differed significantly from non-users in weight gain or change in lean body mass.
- There was some low-quality suggestion that progestin-injection users had slightly higher weight gain than controls. Adolescents using progestin-only pills or progestin-only intrauterine devices (IUDs) had greater loss of mean body weight2.
Early forms of birth control possibly caused fluid retention.
- Early forms of combined oral contraceptives had much higher doses of estrogen and progestin. They may have caused some women to gain weight. Estrogens can indirectly affect how the body handles water3. The weight gain is thought to have been related to retaining fluid.
- Today’s contraceptives have amounts of estrogen and progestin that are a fraction of those used in earlier versions.
Wight gain is normal as people age.
- Women who believe they’ve gained weight because of their birth control might be mistaken. They may have gained weight due to other factors entirely.
- Studies have found that women gain 1 to 2 pounds per year from early adulthood through middle age4.
- Many women take hormonal birth control for five to 10 years or longer.
- Ten or twenty pounds of weight gain over a decade could be easy to blame on hormonal birth control.
Most women shouldn’t worry that using hormonal contraceptives will cause them to gain weight.
- Cochrane Database of Systematic Reviews, January 2006.
- Cochrane Database of Systematic Reviews, August 2016.
- Journal of Applied Physiology 87, September 1999.
- Centers for Disease Control and Prevention, January 2016.