Finasteride cuts the risk of developing prostate cancer by 25%. Yes, that finasteride, the stuff millions of guys use to stop hair loss and pee like a garden hose!

The heartening news derives from a final analysis of the Prostate Cancer Prevention trial, a multicenter prospective randomized study of 19,000 men.

The survival benefit had actually been reported years ago, but at the time it was bundled with the disquieting news that finasteride seemed to cause an uptick in more aggressive forms of prostate cancer.

But now it’s official and strange though it may seem, the apparent negative association turned out to be a manifestation of yet another benefit of finsateride–it facilitates diagnosis of the more virulent cases.

“The goal of developing a chemo-preventive agent that can reduce the risk of prostate cancer has been achieved, and that is…major,” NIH Barnett Kramer told the Washington Post.

In fact based on the newly interpreted findings, Kramer-led guidelines development teams at the American Society of Clinical Oncology and the American Urological Association co-released statements encouraging men that normally get screened for prostate cancer to speak to their physicians about the matter.

The guidelines stopped short of recommending that guys should take the drug.

A call like that would precipitate ten million  finasteride prescriptions in the blink of an eye.

That would be a windfall for Merck but it may not be cost-effective from a societal perspective.

Roughly 71 men would have to take the drug for 7 years in order to prevent one case of prostate cancer.  That’s a lot of exposure to potential side effects which, although rare and reversible, include impotence and decreased libido.

And since finasteride can run 3 bucks a day, it would cost $500,000 for each “prevented” case of prostate cancer, a high figure since in many cases the disease is rather indolent.