As women age, many begin to see a substantial drop in their libido. In some cases, it may be fatigue, emotional stress or lack of an available partner. But in some women, it's the dramatic loss of their natural supply of the hormone testosterone.
To help women restore their lost sex drive, researchers at the University of Michigan are testing whether low doses of testosterone, given through a patch, can help correct low libido in women.
While testosterone is traditionally considered a male hormone, women make testosterone as well. Testosterone can be a key contributor to a woman's sexual desire.
As women age, their testosterone levels drop so that at age 50 it's roughly half the level it was at age 25. Still, that's typically enough to fuel a sex drive.
"For many women, a reduced sexual interest stems from emotional or physical factors such as a health problem, stress or fatigue. One of the alternatives for women who are having a significant drop in their own testosterone levels - and where other physical and emotional factors have been ruled out - is the use of low doses of testosterone," says Nancy Reame, a research scientist in the Medical School's Reproductive Sciences Program.
The women most likely to benefit from this testosterone therapy are those who have had a hysterectomy or their ovaries removed, which means they produce very little natural testosterone. Women with a uterus taking hormone therapy for severe menopause symptoms also may experience a drop in testosterone as a side effect of those medications.
In phase 3 clinical trials that were conducted in the United States, Canada and Australia, women received very low doses of testosterone through a skin patch. The thin, nearly transparent patch, is worn on the abdomen. A similar patch using higher doses of testosterone has been used for several years to treat men with low libido. The doses are significantly lower for the female patch, though, because if testosterone levels get too high in a woman, it could cause masculine traits such as a lower voice, facial hair or increased body hair.
In phase 2 trials, conducted a year ago, the testosterone patch proved to be helpful to women experiencing low libido. The phase 2 trials focused on safety issues. In the phase 3 trials researchers at U-M and elsewhere are assessing how effective testosterone was at improving sexual interest and activity.
"This study will hopefully give us an answer, or at least a piece of the puzzle, about women's sexuality," says Reame, lead researcher for the study at U-M. "It's important that women understand being sexual goes on long after menopause and is part of normal, healthy functioning for the rest of their lives. If we can understand how testosterone fits into this, the better it will be for us all as we get older."
Low sexual interest may affect as many as 40 million women, experts estimate. But testosterone therapy is not appropriate for all women. Stress, depression or hypothyroidism can all be to blame for a decreased sex drive. Medications such as antidepressants, blood pressure drugs or birth control pills can affect sex drive. Fixing the problem may be as simple as tweaking your dosage or switching to a different drug, and testosterone therapy would be inappropriate.
"We're talking about a relatively small proportion of women who might experience low libido, specifically because of low testosterone levels and not because of other kinds of issues, emotional problems or stresses in their lives," Reame says.
But for that group of women, testosterone therapy may be their only chance at a normal sex life.