Birth control pills may get a pass when it comes to causing weight gain — at least according to most research — but not injectable birth control.
Currently, more than 2 million U.S. women, including 400,000 teens, rely on a once-a-month shot — known as Depo-Provera, or DMPA — as their method of birth control. But the shots, which the Food and Drug Administration approved for contraceptive use in 2004 and which offer a relatively inexpensive and highly effective method of pregnancy prevention, can trigger substantial weight gain.
One of the most comprehensive studies on the topic to date was conducted at the University of Texas and published in the American Journal of Obstetrics and Gynecology in March 2009. It started with 703 women ages 16 to 33. The women chose from three methods of birth control: DMPA shots (240 subjects), oral contraceptives (245) and a nonhormonal method of birth control such as a barrier method or abstinence (218).
When researchers compared the three groups after 36 months, DMPA users were more than twice as likely as women using nonhormonal birth control or oral birth control to have become obese. The average weight gain for DMPA users over three years was 11.2 pounds, but 25% gained 24 pounds in the first year.
"They ballooned," said author Abbey Berenson, director of the Center for Interdisciplinary Research in Women's Health at the UT medical branch.
The women using oral contraceptives did not gain more weight than the nonhormonal group (3.3 pounds compared with 4.6 pounds), but they did have an increase in body fat and a decrease in lean muscle mass. Significantly, the study was hampered by the number of women who dropped out.
"Trial results would have been strengthened by including weight change data for women who did not complete the trial," reported Berenson, a professor of obstetrics and gynecology. Of the 703 women who began the study, only 186 completed it.
The No. 1 reason women dropped out: weight gain.