It depends on the woman - and how much you give her. Although testosterone is known as the male hormone, women also naturally produce significant quantities. In fact, there is roughly four times more testosterone than oestrogen in a young woman's blood; spare testosterone is converted to oestrogen. So when a woman's testosterone level drops (as happens during the menopause, for example) it can cause symptoms from tiredness to a loss of sex drive.
This is where testosterone implants come in. Prescribed as a hormone replacement therapy to artificially raise the testosterone level to "normal" levels, the implants hit the headlines this week when a Harley Street doctor said he had given them to five women MPs. (Gynaecologist Malcolm Whitehead said in New Statesman magazine that the MPs asked him for the implants to compete better with male colleagues in debates and meetings.)
Women MPs subsequently questioned by curious newspapers angrily denied that they needed such a chemical boost. But the idea itself isn't nonsense, says hormone therapy consultant Malcolm Carruthers, chairman of the Andropause Society. "Women who have had the implants say they do make them feel more confident and more dynamic," he says. "The psychological effects are very real_they can lift the fog of lethargy and depression that some women get post-menopause."
Testosterone is important for brain function, he says, and the hormone has been linked to preventing conditions such as Alzheimer's disease.
The testosterone implants are controversial. Some experts argue that they are of little benefit for women, and point out that they can produce side effects such as acne and an increase in facial hair. These generally go away when the treatment ends, but some women do experience an irreversible deepening of the voice.
More extreme testosterone treatment is given as part of female-to-male transitions, among other things to encourage hair and muscle growth.