Women using depot medroxyprogesterone acetate (DMPA), commonly known as the birth control shot, gained an average of 11 pounds and increased their body fat by 3.4 percent over three years, according to researchers at the University of Texas Medical Branch (UTMB).
However, women who switched to nonhormonal contraception began to slowly lose the weight and fat mass they gained – nearly four pounds over two years, while those who used oral contraception after the shots gained an average of four additional pounds in the same time span. The amount of weight gain was dependent on the length of time DMPA was used, as the rate of weight gain slowed over time.
The study, which appears in the March 4 issue of the American Journal of Obstetrics and Gynecology , is one of the most comprehensive studies of its kind.
DMPA is an injected contraceptive administered to patients every three months. More than two million American women use DMPA, including approximately 400,000 teens. DMPA is relatively inexpensive compared to some other forms of birth control, has a low failure rate and doesn't need to be administered daily, which contributes to the contraceptive's popularity.
"Women and their doctors should factor in this new data when choosing the most appropriate birth control method," said lead author Abbey Berenson, M.D., professor in the Department of Obstetrics and Gynecology and director of the Center for Interdisciplinary Research in Women's Health at UTMB.
"One concern is DMPA's link to increased abdominal fat, a known component of metabolic syndrome, which increases the risk of cardiovascular disease, stroke and diabetes," said Berenson.
The study followed 703 women in two age categories, 16- to 24-years-old, and 25- to 33-years-old, using DMPA, oral (desogestrel) or nonhormonal (bilateral tubal ligation, condom or abstinence) contraception for three years. DMPA users who discontinued this method and selected another form of birth control were followed for up to two additional years. Throughout the course of the study, researchers compared changes in body weight and composition and took into account the influence of age, race, caloric intake and exercise, among other factors.
When researchers compared all three groups, DMPA users were more than twice as likely as women using nonhormonal or oral birth control to become obese over the next three years. "The findings are worrisome; however, more research is needed to determine if DMPA use directly contributes to obesity-related conditions and puts patients' overall health at risk," said Berenson.