Over the past 5 years the testosterone supplementation therapy (TST) market has grown rapidly.Testosterone is now the second fastest growing medication in the United States.From 2005 to 2009 spending on testosterone jumped 115.5%, and the number of prescriptions filled increased 64.5%.There are many reasons for the rapid growth of the TST market.We have an aging population with the number of U.S.men 65 and older increasing 2-3 times faster than the number of men younger than 65.Furthermore, recent data demonstrate an increased association between poor general health, and possibly mortality, and low serum testosterone levels.There is now less concern for the development of prostate cancer after TST, making it a more attractive treatment option.Finally, new drugs entering the TST market with increased promotion, marketing, and direct-to-consumer advertising,are also driving market growth.