In articles published in the January issue of Mayo Clinic Proceedings, Mayo Clinic physicians call for large studies to help clinicians and patients make informed decisions about when testosterone should be prescribed.

"One of the initial surprises is how limited the research evidence is regarding whether testosterone is an effective treatment for sexual dysfunction while being safe from the cardiovascular disease standpoint," says Victor M. Montori, M.D., MSc, lead researcher for Mayo Clinic's Knowledge and Encounter Research Unit, and an author of the two studies in Mayo Clinic Proceedings. "There is no way for physicians to be certain when prescribing testosterone that, on average, it's doing more good than harm."

Both studies involved review and meta-analysis of randomized trials to assess the effect of testosterone on sexual dysfunction and cardiovascular events. Authors determined that no strong evidence exists showing testosterone doesn't cause cardiovascular harm and results regarding its impact on sexual dysfunction are inconsistent.

In 2004, the Endocrine Society established a task force to generate evidence-based guidelines about the use of testosterone in treating men. Dr. Montori says Mayo researchers joined the effort in order to help the Endocrine Society provide recommendations based on up-to-date research.

"We found that the evidence for whether men are better off being treated with testosterone is much weaker than the evidence for giving estrogen to post-menopausal women was before the big estrogen trials came out," Dr. Montori says.

Despite the weak evidence supporting testosterone's efficacy, drug companies have successfully driven its sale, Dr. Montori says. Currently, physicians may be prescribing testosterone to otherwise healthy men who report poor quality of life, limited sex drive and fatigue and may have somewhat low testosterone levels.

These clinicians and their patients will be "thoroughly shocked" to discover the limited evidence supporting the drug's effectiveness in treating sexual dysfunction and the limited data supporting its cardiovascular safety, Dr. Montori says. "Researchers should conduct trials measuring the outcomes of testosterone treatment that are important to patients in order to avoid repeating the estrogen disaster," he says.

In an editorial accompanying the testosterone studies, physicians from the University of Rome agree that there isn't enough known about testosterone treatment. Andrea Isidori, M.D., Ph.D., and Andrea Lenzi, M.D., Ph.D., say researchers only have begun to explore the potential effects of testosterone, and also call for rigorous trials.

Along with Dr. Montori, authors for the Mayo Clinic Proceedings article on testosterone use in men with sexual dysfunction are Enrique Bolona, M.D.; Maria Uraga, M.D.; Rudy Haddad, M.D.; Michael Tracz, M.D.; Kostandinos Sideras, M.D.; Cassie Kennedy, M.D.; Sean Caples, D.O.; and Patricia Erwin, all of Mayo Clinic.

Authors for the article on testosterone and cardiovascular risk in men are, along with Dr. Montori; Rudy Haddad, M.D.; Cassie Kennedy, M.D.; Sean Caples, D.O.; Michal Tracz, M.D.; Enrique Bolona, M.D.; Kostandinos Sideras, M.D.; Maria Uraga, M.D.; and Patricia Erwin, all of Mayo Clinic.

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