Healthy men over age 55 should consider taking finasteride, a drug marketed under the name Propecia for treating baldness but that may also prevent prostate cancer, two top U.S. medical groups are advising.

The guidelines, released Tuesday by the American Society of Clinical Oncology (ASCO) and the American Urological Association (AUA), recommend that healthy men consider taking finasteride and discuss the option with their doctor.

Finasteride is already used to treat prostate enlargement symptoms but recent research suggests it may also be beneficial in preventing the disease from developing at all in healthy men.

The drug is part of a family of drugs called 5-ARIs that inhibit prostate cancer by lowering the level of the hormone dihydrotestosterone, which can contribute to the cancer's growth.

The drugs, sold under such brand names as Propecia, Proscar and Finpecia, are also used to treat male-pattern baldness and enlarged prostate (benign prostatic hyperplasia).

The panel based its recommendations on several studies -- in particular the Prostate Cancer Prevention Trial (PCPT), which made headlines when it was published in the New England Journal of Medicine in 2003.

That study compared finasteride against placebo in healthy men over 55 who took the drug for one to seven years and received regular prostate cancer tests. The results showed that finasteride could reduce the relative risk of the disease by about 25 per cent.

The studies also set aside earlier worries the drug might promote aggressive prostate cancer in some men.

Panel co-chair Dr. Barry Kramer, associate director for disease prevention at the National Institutes of Health, told reporters Tuesday he thinks finasteride "is a legitimate intervention" just like tamoxifen has been proven to decrease the risk of breast cancer in women at high risk of breast cancers.

But he stressed that the panel is not recommending that all men take the drug; they simply should discuss the option with their doctors.

As well, men already taking finasteride or other similar drug for other conditions should talk to their doctor about continuing the drug for the prevention of prostate cancer.

Kramer notes that 5-ARIs can cause side effects in some men, including erectile dysfunction, impotence and breast tenderness.

Dr. Howard Sandler of Cedars-Sinai Medical Center in Los Angeles, speaking for the American Society of Clinical Oncology, said some men may want to use it on a trial basis.

"If I tried the medication for a month or two and I got some side effects, then for me personally the benefit wouldn't be worth the risk," Sandler told reporters.

And panel co-chair Dr. Paul Schellhammer added that while studies have shown that the drugs can decrease the incidence of prostate cancer, doctors still don't know whether death rates from prostate cancer would be reduced.

"However, the demonstrated effect of 5-ARIs in reducing prostate cancer incidence makes it reasonable to recommend them for use to prevent the disease," he said.

The guideline will be published in the March issues of the Journal of Clinical Oncology and The Journal of Urology.

A patient guide is also available on ASCO's patient website.