Proponents hope the patch called Intrinsa will prove to be a counterpart to Pfizer Inc.'s popular male impotence pill Viagra. No medicines are U.S.-approved for treating sexual problems of women.

P&G's patch delivers a steady dose of testosterone, one of the hormones that spurs sexual desire. Opponents said they were worried months or years of testosterone therapy, which was studied in combination with estrogen, may be dangerous.

The hormones estrogen and progestin were prescribed to women for years as hormone replacement therapy (HRT) following menopause before risks of heart disease and breast cancer came to light.

Studies of Intrinsa so far are "grossly inadequate to assess the risk of extended treatment. I hope we don't have to go through another HRT scandal to learn this again," said Leonore Tiefer, a New York University School of Medicine psychologist.

The advisory panel, a group of experts from outside the U.S. Food and Drug Administration, is expected to vote later Thursday on whether to recommend approval for Intrinsa. The FDA usually follows the advice of its panels.

P&G said its research showed Intrinsa helped women who were distressed by a lack of sexual desire and produced no serious side effects during 24-week trials. The company has proposed studying Intrinsa's safety for five years after approval.

"We feel very strongly the efficacy and safety data are adequate to support approval," Joan Meyer, P&G's senior director for new drug development, told the panel.

Roslyn Washington, who was treated with Intrinsa in clinical trials, said low libido had left her feeling "frustration and a sense of inadequacy."

Intrinsa produced "a noticeable increase in my libido, and I would like to experience those feelings again," she said.

P&G studied about 1,000 women who said they were bothered by low sex drive and, on average, reported three satisfying sexual experiences per month. The number increased to five for women who were treated with Intrinsa, but also rose to four for women given a dummy patch.

"Is an increase in approximately one sexually satisfying encounter a month ... worth the possibility of an increase in breast cancer or coronary artery disease?" asked Dr. Sidney Wolfe, head of Public Citizen's Health Research Group. He urged the FDA panel to reject the drug.

The FDA is under fire for paying scant attention to the safety risks of some drugs and is expected to closely consider potential risks of Intrinsa.

FDA staff reviewers said they were concerned the manufacturer's proposed five-year study would be inadequate to find serious risks.

P&G is aiming initially at a narrow group of about 2 million women who have undergone removal of their ovaries, the source of half the body's testosterone, and are bothered by a lack of sexual desire.

Some critics worry the company will launch a flashy advertising campaign that will interest many more women.

Shares of Cincinnati-based P&G, maker of consumer products including Tide detergent and Crest toothpaste, were up 78 cents, or 1.43 percent at $55.44 on the New York Stock Exchange.