Prostate cancer is the most common type of cancer in American men; one in six will be diagnosed with the disease in their lifetime. Now, a new study published in the New England Journal of Medicine has shown that a common baldness drug can reduce the risk of low-grade, less aggressive prostate cancer by 43 percent.

The study followed 18,800 middle-aged men, starting in the mid-1990s. Over the course of seven years, half of the men took a drug called finasteride, better known as the baldness treatment, Propecia, its Merck brand name, though it's also prescribed under other names to treat prostate enlargement. The other half took a placebo. Checking up on the men after 18 years, the researchers found that men taking the drug had a 30 percent lower risk of developing any type of prostate cancer than men taking the placebo. The finasteride takers also had a 43 percent lower risk of developing slower growing, low-grade cancers. Men on finasteride had a slightly higher risk than men on the placebo of developing high-grade, aggressive prostate cancer, but no greater risk of dying from it: The 15-year survival rates of men in both groups, whether they developed cancer or not, were the same, as were the 10-year survival rates of men in both groups diagnosed with prostate cancer. On another note, it has also been shown that some Propecia users (a little more than 1 percent by the drug maker's account) experience erectile dysfunction from the drug.

Even if it doesn't catch the most dangerous cancers, finasteride could help men by saving them from diagnosis and treatment of less aggressive tumors. The ubiquity of PSA testing to screen for prostate cancer has led to frequent detection of low-grade tumors that are unlikely to be fatal, even if left alone. Treating them with surgery and radiation, however, as some men opt to do, can have unpleasant sexual and urinary side effects – and even watchful waiting, an approach many doctors now recommend, can be expensive and stressful. "Finasteride won't save lives, but it will make the living of lives much higher in quality," says Ian Thompson, a urologic oncologist at the University of Texas Health Sciences Center in San Antonio, who led the study. "You can achieve, in a man who's taking finasteride, equivalent survival to the man having regular PSA testing," while being far less likely that he'll be diagnosed with cancer.