Getty ImagesSweaty, sleepless nights. Inexplicable grouchiness. Weight gain, headaches, and no sex drive. Many women approaching menopause can relate—and so can Mike Coleman.

Last year, a string of restless nights sent the 46-year-old insurance agent from Lineville, Ala., to his doctor. After a blood workup, Coleman was informed that his testosterone levels were below normal, and were likely to blame for the symptoms he'd been experiencing.

"It made sense," he says. "My energy levels were not what they used to be. But you kind of think, ‘How could this happen to me?' "

Coleman's condition isn't all that rare. Quite a few men—up to 25%—have testosterone levels that fall below normal in middle age, and in some cases this transition causes a collection of symptoms that has come to be known as "male menopause" (or "manopause").

"Testosterone levels gradually decline with aging, usually around age 40," says Alvin Matsumoto, MD, a professor of geriatric medicine at the University of Washington School of Medicine, in Seattle. Although the decline is natural, Dr. Matsumoto adds, "that doesn't mean it has no physiological or clinical consequences or shouldn't be treated."

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More and more doctors seem to agree. Between 1999 and 2008, the number of prescriptions filled in the U.S. for testosterone gels, shots, and patches—the first-line treatment for most men—increased by more than 400%, to 3.3 million.

Testosterone treatments in men of middle age and older are largely unproven, however, and they carry a risk of serious side effects. The sharp increase in their use has led some experts to wonder whether testosterone is being over-prescribed—and whether the so-called male menopause needs to be treated at all.

Next Page: How common is it? [ pagebreak ]How common is it?
Male menopause—or late-onset hypogonadism, as the condition is officially known—earned its nickname for a reason. It resembles the changes fortysomething women undergo, and the most common symptoms include a flagging libido, hot flashes, fatigue, weakness, insomnia, moodiness, and weight gain, all of which are also well-known symptoms of (female) menopause.

But the comparison only goes so far. Unlike the relatively swift changes that occur during menopause, testosterone in men tends to decline slowly over many years and isn't always noticeable. Only a fraction of men with low testosterone develop problematic symptoms, whereas most menopausal women experience at least a few hot flashes.

While as many as 25% of men 30 and older have low testosterone levels, only about 5% experience symptoms severe enough to warrant testosterone therapy. Although the symptoms are rare, many doctors have begun testing more middle-age men for low testosterone. This trend has led to wide-ranging—and perhaps inflated—estimates of how common male menopause is, says David Zahaluk, MD, a family medicine physician at Baylor Medical Center, in Carrollton, Texas.

And it's not always clear that low testosterone is to blame for the symptoms that plague the 5% of men being treated, because they can be easily confused with those stemming from other health problems, such as stress, depression, or heart disease. "When you come in and say, ‘I'm tired,' there are so many [potential] causes," says Dr. Zahaluk, who recommends a testosterone test as part of an annual physical. "It may well not be low testosterone, but it won't be checked unless there's awareness of it."

Earlier this year, for the first time, researchers in Britain tried to pinpoint the symptoms that are most closely linked to low testosterone. Only three—erectile dysfunction, fewer morning erections, and fewer sexual thoughts—were reliably connected to testosterone levels, the researchers found. Six others—including low energy, fatigue, and difficulty engaging in physical activity—were linked less closely or not at all to low testosterone. The study concluded that far fewer men than previously thought—only about 2% of men between the ages of 40 and 80—are actually experiencing something that can be called male menopause.

This and other research suggests that treatment is called for only when low testosterone and menopause-like symptoms occur together, says Dr. Matsumoto. "For a long period of time, people have treated individuals with only a low testosterone level," he says. "Only more recently has it been appreciated that treatment should only be considered in men with symptoms and signs of low testosterone as well as consistently low levels."

Next Page: To treat or not to treat [ pagebreak ]To treat or not to treat
The FDA first approved testosterone treatments for men with very low levels of testosterone caused by specific medical problems, such as testicular cancer. Studies over the years have concluded that testosterone therapy is effective for these—typically younger—men, but the value of treating men with age-related testosterone loss is still uncertain. The few studies that have been conducted in older men have yielded mixed results about the benefits and risks of this treatment.

That hasn't stopped older men from wanting to be treated—or doctors from treating them. A man with very low testosterone and numerous symptoms—he's lost his libido, can't have sex, is tired all the time, and has no strength—fits the bill for treatment regardless of age, says Dr. Matsumoto. "There isn't any evidence to treat older men like this, but from what we know about younger individuals who have been treated with a combination of these symptoms and signs and very low testosterone levels, we would expect some benefits," he says.

Dr. Matsumoto helped draft a set of updated guidelines for testosterone therapy that were released in June by the Endocrine Society, a professional organization focused on hormone research. He and his colleagues discouraged the general use of testosterone therapy in older men with low testosterone levels unless their levels were consistently low and they complained of significant physical and sexual symptoms.

It's important for patients to discuss the risks and benefits of therapy with their doctors before making a decision, Dr. Matsumoto says. Monthly testosterone treatment can range from $50 to $200, depending on the method used and how frequently treatment is required, so men with relatively mild sexual and physical symptoms may be better off saving their money.

Next Page: Side effects, big and small [ pagebreak ]Side effects, big and small
The cost didn't deter Coleman, who first tried a daily testosterone patch (which he found annoying), and then monthly shots (which he found uncomfortable). Discomfort aside, Coleman did start to feel better on the shots. He slept better, was less grouchy, and also noticed an increase in his libido—at least at first. But after about four to six months, he started to get mild headaches and noticed a spike in his weight after each shot.

"I was dieting, so I'd get down to about 190. And then after I'd have my shot, I might put on 4 to 6 pounds in a week or two, for no apparent reason," he says.

These reactions aren't uncommon and can be a nuisance, but there are graver potential side effects. Testosterone therapy can cause the body to ramp up red blood cell production, throwing off circulation and increasing the risk of heart disease and stroke. And although a link hasn't been proven, it may even up the risk of prostate cancer. "Even in the absence of any evidence, you have to inform patients that's a potential risk because of the experience in women with estrogen replacement and breast cancer," says Dr. Matsumoto.

Because of these potential risks, doctors closely monitor the patients receiving treatment. If their bodies don't absorb testosterone or maintain the effects of treatment, some are even advised to stop replacement therapy. "That's not the majority of cases, but it does happen," says Dr. Zahaluk.

It's far more common for men to stop testosterone therapy because its just not working for them. That was true in Colemans case. He ultimately abandoned his treatment when it failed to boost his testosterone levels into the average range. "I didnt see that I was getting so much benefit as opposed to what I was having to put up with,” he says.