A recent study has suggested that a testosterone patch may improve the libido of postmenopausal women significantly. The research in the Nov. 6 New England Journal of Medicine adds that this libido boost comes with its share of side effects like a possible increase in the risk of breast cancer in women taking the male hormone.

The study was paid for by Proctor & Gamble Pharmaceuticals to get approval for a 300-microgram patch, which it calls Intrinsa, in 2004, specifically for women who had had declines in testosterone levels as a result of having surgically induced menopause. The study authors said the U.S. Food and Drug Administration turned down the manufacturer's request for approval in December 2004, citing a lack of long-term safety data although the patch is available in Europe.

Dr. Susan R. Davis, a professor of women's health at Monash University in Australia and the study's lead author said, "This is the first study to show that when used alone, testosterone administered by a skin patch significantly improves sexual well-being in postmenopausal women."

The study involved 814 postmenopausal women who reported low sexual desire and were not on estrogen therapy. The study ran for 52 weeks and the women were randomly divided into three groups one who got treatment with a patch that delivered 300 micrograms of testosterone daily, one a patch that delivered 150 micrograms of testosterone daily, or a placebo patch. After 24 weeks, the women in the 300 microgram group reported an average of 2.1 satisfying sexual episodes during a four-week period, compared to 1.2 sexually satisfying episodes for those on the lower dose, and just 0.7 satisfying episodes for women on the placebo.

 Four cases of breast cancer were diagnosed among the testosterone users during the study while there were none in the placebo group. Davis said two of the cancers were present but missed at the start of the trial, while the third one occurred in a woman who had been on estrogen therapy for 27 years. "Considering that most women will only end up using testosterone for a couple of years, it is probably safe," she says.

Julia R. Heiman, PhD, who directs the Kinsey Institute for Sex, Gender and Reproduction said, "I think very important questions remain about the safety of this treatment in light of this finding." Heiman urged caution in using testosterone for low libido "until we understand more about its possible link with breast cancer and are better able to predict which patients are more likely to be subject to negative effects."

Dr. Steven Goldstein, an obstetrician and gynecologist at the New York University Langone Medical Center in New York City said, "It shows that in the double-blind, placebo-controlled trial, testosterone does have a positive effect on the frequency of satisfying sexual experiences. But, what about long-term effects?" he asked. "You have to wear this patch all the time. That means you're subjecting yourself to a hormone 24/7," he added.

Davis said, "I believe women have as much right as men to have a choice of therapy if sexual well-being impairs their quality of life," she said, adding, "I think [the testosterone patch] should be made available, because it is both effective and safe."

Tom Millikin, a spokesman for Procter & Gamble Pharmaceuticals said, "We continue to work with the FDA to determine if there is an appropriate pathway forward for Intrinsa, but beyond that we are not providing comment."