Average bone density at the hip fell 2.8 percent one year after starting Depo-Provera and 5.8 percent after two years. Loss of bone density in the spine was similar.

In contrast, average bone loss at the hip and spine was less than 0.9 percent among the comparison group of women, the team reports in the medical journal Fertility and Sterility.

"We clearly show that bone density is lost with DMPA use," Clark told Reuters Health.

She also noted that in mid-November, the U.S. Food and Drug Administration issued a black box warning on Depo-Provera stating, in essence, that bone density is lost and may not be regained, particularly when it is used for more than two years.

"Without information on the magnitude of bone mineral density loss, clinicians cannot weigh the potential benefits of a highly effective method of contraception to the potential problems associated with bone loss. Our study provides this information," Clark said.

She emphasized that most women between the ages of 18 and 35 who are using Depo-Provera for contraception will not have immediate problems related to osteoporosis. However, whether there are long-term problems following menopause will depend on whether lost bone is regained when Depo-Provera is discontinued.

Clark's team is close to completing the phase of their study that is looking at what happens to bone density when women stop using the contraceptive. "It is hard to speculate on recovery without complete data," she said.

The results of a study released in 2002 hint that bone density returns to normal about 15 months following discontinuation.

However, Clark sees a problem with that study. "Most of the women were enrolled after they had been on DMPA for a while, so they did not have baseline data and would have no way of knowing what the true bone loss was since beginning DMPA," she commented.

SOURCE: Fertility and Sterility, December 2004