Millions of American men use a prescription testosterone gel or injection to restore normal levels of the manly hormone. The ongoing pharmaceutical marketing blitz promises that treating "low T" this way can make men feel more alert, energetic, mentally sharp, and sexually functional. However, legitimate safety concerns linger. For example, some older men on testosterone could face higher cardiac risks.

"Because of the marketing, men have been flooded with information about the potential benefit of fixing low testosterone, but not with the potential costs," says Dr. Carl Pallais, an endocrinologist and assistant professor of medicine at Harvard Medical School. "Men should be much more mindful of the possible long-term complications."

http://www.health.harvard.edu/mens-health/is-testosterone-therapy-safe-take-a-breath-before-you-take-the-plunge