Pfizer’s injectable contraceptive, Depo-Provera (medroxyprogesterone), which was hit towards the end of last year by the double whammy of the start of generic competition and a label change warning of a risk of bone loss with extended use, has been lifted by a new trial suggesting that the latter side effect is reversible.

First introduced by Upjohn in 1992, Depo-Provera is given by intramuscular injection and provides three months’ contraceptive cover. Never a blockbuster, the product has found a modestly lucrative niche among women who find it difficult to comply with an oral contraceptive regimen, with sales running at around $110 million dollars a year ahead of the launch of a generic competitor from Israel’s Teva Pharmaceutical Industries last September.

In November 2004, the US Food and Drug Administration required Pfizer to add a "black box" warning to the drug’s labelling to reflect an increased risk of bone density loss – the early stages of osteoporosis – when it was used for a long time [[22/11/04e]]. The warning effectively placed a ceiling of two years on the length of time a woman should use Depo-Provera, unless other birth control methods are inadequate.

At the time, the FDA said indications were that the bone loss might be irreversible, but a new study published in the journal Archives of Pediatric and Adolescent Medicine (February 2005) gives more encouraging news. The trial, which compared 80 adolescent women on Depo-Provera with 90 control women, backed up earlier data showing that the depot was associated with significantly more bone loss. However, over three years of follow-up, 61 of the women on Depo-Provera stopped taking the contraceptive, and experienced a significant rise in bone density compared to controls.

“These findings are reassuring for those concerned about future risk of fractures,” the study’s principle author, Dr Delia Scholes, from the Group Health Cooperative in Seattle, said in a statement. She added that the information would make it easier for young women to balance the risk of side effects with an unwanted pregnancy.

Pfizer had further negative news for Depo-Provera last September, after a study was published suggesting that women taking the product had a threefold higher risk of contracting sexually-transmitted infections than those on oral contraceptives.