Testosterone replacement therapy needs more studies

Testosterone is a hormone made in the testes that helps men to maintain male characteristics.

Some claims have been made that testosterone can raise muscle mass, sharpen memory, boost sex drive and improve energy. But none of these are proven.

One study shows testosterone replacement in men with angina or chronic heart failure raises their exercise tolerance. Another study says men ages 40 to 79, who naturally produce higher levels, have lower death rates from many diseases.

But these results are uncertain. Even the study on exercise tolerance noted that the effects trail off after one year. And, there is no proof that replacement therapy improves disease survival rates for those with low testosterone.

Experts say more studies are still needed to understand the role - if any - that testosterone replacement therapy plays in the treatment of many conditions.