A class of drugs meant to improve symptoms of an enlarged prostate gland actually increase the chance of getting a more serious form of prostate cancer, U.S. health officials said on Thursday.
However, they also said the drugs' benefits outweigh the risks.
The drugs in the group include Merck & Co's Proscar and GlaxoSmithKline's Avodar and Jalyn, as well as Merck's Propecia, which is approved to treat male pattern hair loss.
The Food and Drug Administration said it revised the labels on all such drugs, called 5-alpha reductase inhibitors (5-ARI), to include the risk after reviewing two large studies.
The randomized controlled studies found that daily use of 5-ARIs for several years decreased the chance of getting lower-risk forms of prostate cancer but made it more likely that patients would get a high-grade prostate cancer, which grows and spreads more quickly.
"This risk appears to be low, but health-care professionals should be aware of this safety information, and weigh the known benefits against the potential risks when deciding to start or continue treatment with 5-ARIs in men," the FDA said on its website.
The 5-ARI drugs are known clinically as finasteride and dutasteride and are used to treat benign prostatic hyperplasia (BPH), or prostate enlargement, a common condition in men over 40. Propecia, for male baldness, includes a smaller dose of finasteride.
The FDA said about five million male patients were given a prescription for a 5-ARI from 2002 to 2009. The drugs' benefits in treating BPH still outweigh any risks, it said.
Another class of medicines known as alpha-blockers can also be used to treat symptoms of BPH. Drugs of this type include Astellas Pharma's Flomax, Pfizer Inc's Cardura, and Rapaflo from Watson Pharmaceuticals.