Procter & Gamble's Intrinsa testosterone patches appear to not do much to boost a woman's sex drive after menopause and their long-term safety is unclear, a review found on Tuesday.

Intrinsa is licensed for use in Europe but not in the United States where, in 2004, regulators voted against approving the patches that deliver the male hormone, citing lack of evidence for their long-term safety.

"The published evidence so far is based on highly selected women and only shows small improvements in sexual parameters and large placebo responses," Ike Iheanacho, editor of the Drug and Therapeutics Bulletin, which published the review of published studies.

"Also the long term safety of the treatment is unknown. Unwanted side effects are common and not always reversible. For all these reasons, we cannot recommend Intrinsa for use in women with sexual dysfunction."

Procter & Gamble could not be immediately reached for comment.

Intrinsa is licensed for women with hypoactive sexual desire disorder, characterized by persistently diminished or absent desire for sex. A person with the disorder can function sexually.

The patch, which delivers a daily dose of testosterone, was recently licensed in Britain for women who have gone through menopause due to womb and ovary removal, the researchers said.

Some studies have suggested a diminished sex drive after menopause could be caused by low levels of hormones such as testosterone.

Both men and women produce testosterone, although men make more of it.

Iheanacho and colleagues reviewed a handful of studies looking at Intrinsa that included nearly 4,000 women. Most of the trials lasted less than six months, which made it difficult to determine long-term safety, the researchers said.

The key trials for the patches also involved a select group of women in menopause due to surgery and they did not look at other mental or physical conditions that might have affected sex drive, the review found.

Side effects were common and the improvements in sex drive was small, with many women not treated with the patch reporting improvements, Iheanacho and his team added.