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Clinical Trial









The Testosterone Trials (TTrials) were a collection of seven trials designed to investigate the efficacy of increasing the serum testosterone concentration of older men who had low serum testosterone concentrations to that of young men. The trials were funded by the following components of the National Institutes of Health (NIH): National Institute on Aging (NIA); National Institute of Neurological Disorders and Stroke (NINDS); National Institute of Child Health and Human Development (NICHD); and, National Heart, Lung, and Blood Institute (NHLBI).


Testosterone levels in men gradually decline with age, as do libido, walking speed, energy, hemoglobin and bone mineral density. Young men who have severe hypogonadism also have these deficiencies, and testosterone treatment corrects them. The TTrials were designed to determine if testosterone treatment of older men with mild-moderate hypogonadism would also improve these parameters.

Study Design

The TTrials were a set of seven interventional clinical trials, which began in 2009 and concluded in 2018. Each had a specific focus: Sexual Function Trial; Physical Function Trial; Vitality Trial; Cognitive Function Trial; Bone Trial; Cardiovascular Trial; and Anemia Trial. A total of 790 participants were enrolled at 12 clinical sites across the United States. Participants were men aged 65 and older who had early morning serum total testosterone concentrations <275 ng/dL. Men were excluded from participation if they had or were at risk of developing a disease or condition that might be worsened by testosterone treatment or would interfere with study procedures and outcomes. Participants were allocated to receive either a testosterone gel or a placebo gel, which they applied once a day for 12 months. In all seven trials, participants underwent specific assessments at predetermined intervals and were monitored for adverse effects of testosterone treatment.

Interventions/Treatment Groups

Participants were treated with testosterone or placebo gel for one year. Participants in the testosterone group were monitored regularly and the dose adjusted to attempt to keep the testosterone concentration within the normal range for young men.


During the trial period, participants were regularly assessed for changes in sexual activity, sexual desire, and erectile function (Sexual Function Trial); walking distance and physical function (Physical Function Trial); fatigue score, total positive and negative affect scores, and depressive symptoms (Vitality Trial); delayed paragraph recall score, visual memory, spatial ability, and executive function (Cognitive Function Trial); hemoglobin levels (Anemia Trial); bone mineral density and bone strength (Bone Trial); and non-calcified coronary artery plaque volume, total plaque volume, and coronary artery calcium score (Cardiovascular Trial).


Testosterone treatment, compared to placebo, had many significant effects. Testosterone treatment significantly increased all aspects of sexual function, including sexual activity, sexual desire, and erectile function. Testosterone treatment increased hemoglobin concentration in all men and corrected anemia. Testosterone treatment increased volumetric bone density and estimated bone strength. Testosterone treatment was associated with smaller but still statistically significant improvements in walking speed, mood, and depressive symptoms. Testosterone treatment was also associated with an increased volume of non-calcified coronary artery plaque. The clinical significance of this increase is uncertain, because the TTrials were not sufficiently large enough or long enough to assess cardiovascular risk. Testosterone treatment did not have an effect on any aspect of cognitive function.