Washington, DC -- Concerns about the effects of depot medroxyprogesterone acetate (DMPA)—the contraceptive shot—on bone mineral density (BMD) should not prevent clinicians from prescribing this method of contraception nor should its use be limited to two years, according to a new Committee Opinion released today by The American College of Obstetricians and Gynecologists (ACOG). Though DMPA has a known link to BMD loss, studies show that most of the loss is temporary and is similar to the BMD loss caused by pregnancy and breastfeeding.
"Women should be thoroughly counseled about the risks and benefits of DMPA so they can make an informed decision about whether it's right for them," said Denise Jamieson, MD, chair of ACOG's Committee on Gynecologic Practice. "Many women would choose the theoretical risk of future fracture over the very real risk of an unintended pregnancy. For example, a teen at high risk of pregnancy—who faces a similar rate of bone loss from either pregnancy or DMPA use—may find the risk worthwhile."
In 2004, the US Food and Drug Administration issued a black box warning discouraging the use of DMPA for more than two consecutive years. The warning states that prolonged use of DMPA may result in significant loss of BMD, that bone loss is greater the longer the drug is used, and that the loss may not be completely reversible after discontinuation. It also advises that DMPA use beyond two years should only be considered if other contraceptive methods are inadequate. Additionally, one DMPA manufacturer has recommended bone scans for women after two years of use.
Bone loss does occur, especially within the first two years of DMPA use. But evidence suggests that within one to two years after discontinuation, BMD in most adolescents and women rebounds to near baseline levels. The FDA's warning is based on intermediate effects on BMD, which may or may not be relevant to increased risk of fracture. Studies show that former adult DMPA users have BMD rates similar to women who have never used the drug.
Bone loss in reproductive-aged women is not exclusive to DMPA users. Adult women show similar rates of temporary bone loss during pregnancy and breastfeeding (2%-8% and 3%-5%, respectively) when compared with BMD loss sustained by DMPA users (approximately 3%-5%).
Adolescents using DMPA lose BMD at a time when their BMD would typically increase, which can be a cause of concern. However, while low BMD is linked to an increased risk of fracture in older women, no studies have linked DMPA-related BMD loss with increased rates of fracture in younger women with a low-fracture risk.
More than 2 million American women use DMPA, including approximately 400,000 teens. Injected once every three months, it is a safe method of birth control that is between 97% and 98% effective at preventing pregnancy. "DMPA has a number of characteristics that make it particularly appealing to certain populations such as adolescents or women who may have a hard time successfully using a daily or partner-dependent method of contraception," said Dr. Jamieson. "Some women also prefer it over other methods of contraception because of the privacy that it provides. Increased use of DMPA has likely been a contributing factor in the drop of adolescent pregnancy rates in the past decade."
Daily exercise and age-appropriate calcium and Vitamin-D intake should be encouraged in DMPA users, especially in teens, who often do not get enough calcium. Although studies have shown that low-dose estrogen supplementation slows bone DMPA bone loss, ACOG does not currently recommend it. Clinicians should counsel women on the side effects of DMPA, such as breakthrough bleeding, to curb the high discontinuation rate for this contraceptive method.
ACOG recommends that other effective, long-term methods of contraception that have no effect on bone density—such as contraceptive implants and intrauterine devices—should also be considered as first-line methods for adolescents.
Committee Opinion #415, "Depot Medroxyprogesterone Acetate and Bone Effects," is published in the September 2008 issue of Obstetrics & Gynecology.