Testosterone therapy is an unproven yet growing practice among aging men that urgently needs closer study to establish its benefits and risks, according to a one-year study by the Institute of Medicine.
The report, released Wednesday, noted that medical studies on the hormone's effects in men aged 65 or older are scant, short and inconclusive. Supposed benefits in such areas as strength, sexual function, mental acuity and overall well-being have not been proven.
Meanwhile, many doctors worry that the hormone could cause other medical problems, such as increasing the risk for prostate cancer and blood clots, although such risks have not been established.
The study, commissioned by the National Institutes of Health, stopped short of telling doctors to cease prescribing testosterone to older men whose testosterone levels, while lower than in youth, are not severely low or absent.
"We're saying that doctors should think about why they are writing prescriptions ... to look at the literature and consider what we know and what we don't," said Dr. Dan G. Blazer, professor of psychiatry and behavioral sciences at Duke University Medical Center, who was chair of the study.
Testosterone is a sex hormone that declines as men age. Some men make little or none of it, a condition known as hypogonadism, and the Food and Drug Administration has approved testosterone therapy for this condition. Originally administered by injection, the hormone is now available as a patch or gel.
However, doctors often prescribe medications for so-called off-label uses, and testosterone is increasingly being prescribed for men who do not have hypogonadism, but are seeking help with problems associated with aging.
In 2002, more than 1.75 million testosterone prescriptions were written, a 170% increase since 1999. The trend is expected to continue.
Dr. Evan Hadley, an associate director at the National Institute on Aging, said the rising use of testosterone therapy echoes the widespread use of estrogen and progestin in post-menopausal women to offset a host of age-related problems.
After many years of use, an extensive study reported last year that risks of that therapy outweighed the benefits.
In the case of testosterone, "we want to examine these risks and benefits now, rather than wait," Hadley said.
The report was focused specifically on men aged 65 and older. Even less is known about the effects of testosterone on middle-aged men without hypogonadism who may seek the hormone to offset the symptoms of aging.
"There's a big worry about how much use of drugs in that fashion is happening out there," said Dr. Eli Chester Ridgway, an endocrinologist at the University of Colorado Health Sciences Center and president of the Endocrine Society, a professional organization for endocrinologists.
The 17-member scientific panel recommended that trials focusing on men 65 or older with at least one symptom of testosterone shortage be set up as soon as possible. Men at heightened risk for prostate cancer would be excluded.
The first studies would enroll several hundred older men and run for one or two years, to detect any benefit of the hormone. If benefits were identified, longer-term investigations involving thousands of men would follow, to assess potential risks.