Depo-Provera (depot medroxyprogesterone), a popular birth control injection, seems to promote bone loss, and the effects increase over a 2-year period, new research shows.

Dr. Abbey B. Berenson, of the University of Texas Medical Branch, Galveston, and colleagues compared the bone-thinning effects of Depo-Provera, birth control pills, and non-hormone contraception in a study of 191 young women.

Women who used Depo-Provera for 24 months had an average loss in bone density of 5.7 percent. These patients experienced a 3.2-percent loss between months 12 and 24. Those who used pills, by contrast, had a 2.6-percent loss at 24 months.

The results are published in the medical journal Obstetrics and Gynecology.

Depo-Provera “is intended for long-term use,” the authors write. “Thus, additional studies that follow users of this method for extended periods of time and those that determine whether these changes are reversible are critical so that physicians can accurately counsel patients regarding this method.”

SOURCE: Obstetrics and Gynecology, April 2004.