It could have you feeling like a new man

A new medication that arrived in pharmacies last month

is raising the possibility of widespread hormone replacement therapy for men -- much like for post-menopausal women -- even as it raises fears about misuse.

The product, a gel form of testosterone called AndroGel, is approved for use in men with abnormally low levels of testosterone.

Currently, only about 150,000 to 200,000 men are being treated for low testosterone, although the advent of AndroGel could boost that number to 5 million.

But because AndroGel represents the first simple and relatively safe form of testosterone replacement therapy, it is also generating discussion on testosterone as a major component of health and well-being throughout a man's life span.

''Just as Viagra provided a simple way to deal with erectile dysfunction and brought the whole issue out in the open, I think a similar thing is going to happen by having an easily available testosterone preparation,'' says Jed Diamond, a Willits, Calif., psychotherapist and expert on changes in men's health at midlife. ''It will extend this dialogue on men's health.''

Testosterone is a naturally occurring steroid produced by the bodies of both men and women. But it's best known for supplying men with the classic, predominantly male traits of strength, aggression and virility.

Low testosterone, called hypogonadism, has numerous causes, including the loss of the testicles to testicular cancer, pituitary disorders, a genetic disorder called Klinefelter syndrome and normal aging.

Low testosterone causes diminished interest in sex, impotence, reduced lean body mass, decreased bone density and lowered mood and energy levels. In short, it can make a man feel like a greatly dimmed version of his former self, says Robert E. Dudley, chief executive of Unimed Pharmaceuticals in Deerfield, Ill., the manufacturer of AndroGel.

''A lot of men have learned to live with being hypogonadal'' because of a limited array of treatment options, Dudley says.

Studies showed that, besides alleviating the typical symptoms of hypogonadism, AndroGel might help prevent male osteoporosis, which affects about one in five men in old age and can be devastating to very elderly men. Those who suffer hip fractures have a higher death rate than women with the same injury.

''Much to our delight and surprise, within six months (of treatment) we were able to show an improvement in bone mineral density, which was particularly pleasing because many of the subjects had been on other testosterone products (which had not produced evidence of new bone growth),'' says Dr. Ronald S. Swerdloff, chief of endocrinology at Harbor-UCLA Medical Center and the principal researcher on the clinical trials of AndroGel.

There are risks associated with AndroGel, however, including the possibility that the substance could be transferred to another person by vigorous skin-to-skin contact, causing side effects such as hair growth or acne in the untreated person. Testosterone can also cause fetal harm if absorbed by a pregnant woman.

While those complications are rare and can be avoided if the gel is used carefully, men receiving any long-term testosterone therapy face other risks, including higher rates of prostate enlargement and prostate cancer. Testosterone replacement therapy is not recommended for men with breast or prostate cancer.

Men without prostate cancer can take testosterone but should have their prostates checked on a regular basis.

''There is no evidence to this point that testosterone causes prostate cancer,'' Swerdloff says. ''But if you have prostate cancer, the testosterone will cause it to grow.''.

There is also mixed evidence on whether testosterone replacement therapy is good or bad for the heart. AndroGel is not recommended for men with heart disease.

''Does it improve strength and bone, but then men will die of heart attack or prostate cancer? We don't know the answers to that,'' Swerdloff says. ''This requires larger scale studies to answer that.''

For middle-age men who are not at high risk for prostate disease, replacement therapy makes sense, doctors say.

Experts like Swerdloff are both thrilled and worried about such delighted reactions to testosterone gel. Although patients like Smaul need it, other men who do not have clear-cut hypogonadism may benefit as well.

''The question that it leaves is, who do you treat? And if you treat people, what will be the balance of good and bad (effects)?'' Swerdloff says.

That question is difficult to answer, because doctors don't even have a good idea of what ''normal'' testosterone levels are, or how the decline of the hormone, beginning around age 30, contributes to the loss of bone, muscle, libido and energy by the time a man reaches retirement age.

Testosterone increases in puberty and peaks at about age 20 to 30 in the ''normal'' range of about 300 to 1,200 nanograms per deciliter (ng/dL) of blood and then begins to decline, especially after age 50. Testosterone levels vary widely among individuals, and even an individual's levels will vary somewhat from day to day, even hour to hour.

Until there is more research on testosterone, AndroGel will not -- and should not -- become the Grecian Formula of men's health, something everyone over 45 is using to feel a little younger, experts say.

''I think it's very clear that AndroGel is only approved for use in men with low testosterone concentrations. And that is appropriate,'' Swerdloff says.

But will men demand more research to clarify the many questions surrounding testosterone replacement therapy the way women have for estrogen replacement therapy? A 1998 survey of 1,000 men found that 68 percent could not name a single symptom associated with low testosterone.

The baby boom generation, the first of whom are nearing retirement age, may well embrace the idea of hormone replacement therapy for men, Swerdloff says.