ScienceDaily (July 23, 2007) — Men and their physicians need not hesitate to use a drug proven effective in preventing prostate cancer out of concern that it is likely to cause sexual dysfunction, say authors of a study conducted by the Southwest Oncology Group.

The authors, who surveyed more than 17,000 men 55 and older for seven years, reported their results in the July 4 Journal of the National Cancer Institute. The study found that men given finasteride reported on average more dysfunction than did men given a placebo. That small effect diminished over the seven years.

The results allay concerns about a negative side effect associated with finasteride up till now. Physicians usually warn that sexual dysfunction is a possibility when they discuss the drug with patients. Finasteride is an FDA-approved drug for the treatment of benign prostatic hyperplasia, but it is not yet FDA-approved for the prevention or reduction in risk for prostate cancer.

The study's large sample and long follow-up period allowed researchers to examine whether or not finasteride negatively affected sexual function and, if so, whether this effect was lasting, said Carol Moinpour, Ph.D., of the Fred Hutchison Cancer Research Center in Seattle, the study's lead author. She coordinates quality-of-life studies for the Southwest Oncology Group, the nation's largest National Cancer Institute-funded clinical trials network.

The study grew out of the Prostate Cancer Prevention Trial, a large double-blind National Cancer Institute-funded study which found that finasteride, a drug which curbs the proliferation of prostate gland cells, is effective at preventing prostate cancer in men age 55 and older. The 2003 results of that trial, conducted by the Southwest Oncology Group in more than 18,000 men, showed that finasteride could reduce a man's chances of getting prostate cancer by almost 25 percent.

The authors of the newly published sexual function results wanted to assess how many men in the Prostate Cancer Prevention Trial reported experiencing sexual dysfunction, and whether the problems decreased or increased over time. In earlier studies, some men taking finasteride reported decreased libido, impotence and other signs of diminished sexual function. But these studies were short-term and didn't try to assess the effects of age and other health factors, as well as individual variation.

The study authors used two surveys, a widely used Sexual Problems Scale and another questionnaire which they created, the Sexual Activity Scale. They also gathered other data to take into account other health factors that affect sexual function, such as age, medical conditions and smoking status. They surveyed the subjects three times in the first year and then annually for seven years.

"Was this average decrease (in sexual function) an important difference" We concluded it was not," Moinpour said, adding that there were much larger differences due simply to individual variation among men in the trial.

The study suggests that finasteride will cause little or no sexual dysfunction for most men who decide to take it, conclude the authors.