For the first time, leading medical groups are advising millions of healthy men who are regularly screened for prostate cancer to consider taking a drug to prevent the disease.

The advice stops short of saying men should take the drug finasteride, sold in generic form and as Proscar. It is already widely used for urinary problems from enlarged prostates as men age.

However, it has not been widely prescribed as a cancer preventive, and it may carry some risks. The new guidance tells men to talk to their doctors and decide for themselves if the good outweighs the bad.

This advice is bound to be confusing, doctors admit. For one thing, it doesn’t apply to men who choose not to have screening with PSA blood tests, which no major medical groups recommend.

In men who are regularly screened, finasteride can cut the odds of being diagnosed with prostate cancer by about 25 percent.

“If a man is interested enough in being screened, then at least he ought to have the benefits of a discussion” about taking the drug, said Dr. Barnett Kramer, a National Institutes of Health scientist and one of the authors of the new guidelines.

They were published in two medical journals and discussed in a news briefing Tuesday in connection with a cancer conference in Florida. They were written by doctors with American Society of Clinical Oncology and the American Urological Association.

Cost could be a big issue for many men. Finasteride, which must be taken daily, costs $2 to $3 a pill and insurers may not cover it for cancer prevention. Also, to prevent a single additional case of cancer, 71 men would have to take the drug for seven years — another reason this is an individual decision, doctors say.

About 186,000 American men this year will be told they have cancer of the prostate. The disease often is diagnosed from a biopsy after a suspicious PSA blood test, which measures a protein. PSA can be high for many reasons, and there’s no proof that screening saves lives — the reason no major cancer groups recommend it.

Most men over 55 get the test anyway, then face a dilemma if cancer is found. It usually grows so slowly it is not life-threatening, but it can prove fatal. Treatments often cause sexual or bladder control problems.