The widely used male hormone testosterone has not been shown to be either safe or beneficial for the many men who use it to improve their strength and mood, an expert panel of doctors concluded Wednesday.

In a report from the congressionally chartered Institute of Medicine, the panel said that while the drug, which has been approved by the Food and Drug Administration, can be useful for men who suffer from a medical condition, it is “inappropriate for widescale use to prevent possible future disease or to enhance strength or mood in otherwise healthy older men.”

Testosterone, used by more than 800,000 men last year, has become a popular prescription drug for men who believe it can help them build up their muscles, improve their thinking, increase their libido and slow the aging process.

But the IOM review concluded that there was insufficient research to know whether it provided any of those benefits to otherwise healthy men or to gauge the seriousness of known increased risks of prostate cancer and blood-clotting.

“For men whose testosterone is already in the normal range, there is no proof that it makes them better in any way,” said panel member Deborah Grady of the University of California, San Francisco. “If there is no proven benefit for them, they shouldn’t be taking testosterone no matter what the risk. And here there is a possible problem with prostate cancer.”

Some of the increase has been driven by aggressive advertising. On the Web site for the market-leader Androgel, for instance, the company asks: “Fatigued? Depressed Mood? Low Sex Drive? Could be your testosterone is running on empty.”

The FDA has approved testosterone use only for hypogonadism, a usually disease-based condition that results in the production of insufficient amounts of testosterone in the testes.