The Testosterone Trials (TTrials): The Most Rigorous Multi-Outcome TRT Research Ever Conducted

Written by Keen Meds  ·  Reviewed by Licensed Clinical Providers  ·  March 1, 2026

Key Insight: The TTrials enrolled 790 men aged 65 and older across 12 US academic medical centers, running 7 simultaneous randomized controlled trials on different outcome domains — sexual function, walking, bone density, anemia, cognition, cardiovascular health, and vitality.

By 2010, the clinical evidence base for testosterone replacement therapy consisted of dozens of small, heterogeneous trials measuring different outcomes in different populations using different formulations. Some showed improvements in sexual function. Some showed improvements in body composition. Some showed no significant benefit on the outcomes they measured. The small size of individual trials made it difficult to draw reliable conclusions, and the variety of populations studied made cross-study comparison unreliable.

The Testosterone Trials, commonly called the TTrials, were designed to address this fragmentation. Funded primarily by the National Institute on Aging and the National Cancer Institute, and coordinated by a team that included Shalender Bhasin, Peter Snyder, and other leading figures in clinical andrology, the TTrials ran seven simultaneous randomized controlled trials in the same pool of men, measuring a range of outcome domains under identical conditions. The result was the most rigorous and comprehensive assessment of testosterone therapy in older men ever published.

Why a Multi-Trial Consortium Was Necessary

The problem with the pre-TTrials literature was not that it was entirely uninformative. Individual trials had produced credible results within their specific populations and outcomes. The problem was generalizability and statistical power.

Many prior trials enrolled fewer than 100 participants. With that sample size, a trial is unlikely to detect modest but clinically meaningful effects -- the statistical power is insufficient. A trial that fails to detect an effect may genuinely have found a null result, or it may have been too small to detect a real effect.

The fragmentation of prior research also meant that data on different outcome domains -- sexual function, physical function, bone density, anemia, cognition -- came from different patient populations, different diagnostic thresholds for low testosterone, different follow-up durations, and different formulations. Attempting to synthesize these results into a coherent clinical picture was challenging.

The TTrials consortium design addressed these problems by enrolling a single pool of participants, randomizing them across all seven trials simultaneously, and measuring multiple outcome domains in the same men using consistent diagnostic criteria, the same testosterone formulation, and standardized follow-up protocols.

Trial Design: Who Was Enrolled and How

The TTrials enrolled men aged 65 and older from 12 academic medical centers across the United States between 2010 and 2014. Eligibility required a testosterone level below 275 ng/dL confirmed on at least two measurements, plus at least one symptom consistent with testosterone deficiency from each of three symptom domains: sexual dysfunction, low energy or vitality, and physical function limitation.

Participants were randomly assigned to receive either testosterone gel (AndroGel 1%) or placebo gel for one year. Testosterone doses were adjusted to maintain testosterone levels in the normal range for young men (500 to 1000 ng/dL). All 790 participants were enrolled in at least the three primary trials (Sexual Function, Physical Function/Walking, and Vitality). Subsets participated in additional trials based on specific eligibility criteria for bone, anemia, cognition, and cardiovascular outcomes.

The Seven Simultaneous Trials and Their Results

Sexual Function Trial (Primary): The main results, published by Snyder et al. in the New England Journal of Medicine in February 2016, found that testosterone treatment significantly improved sexual activity, sexual desire, and erectile function compared to placebo. The improvements were statistically significant and clinically meaningful in terms of patient-reported outcomes. This was the strongest positive result across all seven trials.

Physical Function / Walking Trial (Primary): Men in the testosterone group walked a slightly greater distance on a 6-minute walk test at 12 months compared to the placebo group. The difference, while statistically significant, was modest in absolute terms and below the pre-specified threshold for clinical significance that the investigators had defined in advance.

Vitality Trial (Primary): Testosterone did not significantly improve self-reported fatigue or vitality compared to placebo in the overall cohort. This was a null result on a domain that many men associate with testosterone deficiency, and it suggested that fatigue or low energy in older men is multifactorial and may not respond to testosterone normalization even when testosterone levels are confirmed low.

Bone Density Trial: This sub-trial found that testosterone significantly increased volumetric bone mineral density in the spine and hip measured by quantitative CT, and also improved estimated bone strength. The effect sizes were substantial and clinically relevant. The bone density findings were among the most clearly positive results across all seven trials.

Anemia Trial: This sub-trial found that testosterone treatment corrected unexplained anemia in a significantly higher proportion of men compared to placebo. Men with unexplained anemia in the testosterone group were substantially more likely to have their hemoglobin normalized at 12 months. The effect was particularly large in men who had no identified cause for their anemia.

Cognition Trial: Testosterone did not significantly improve cognitive performance compared to placebo on the neuropsychological test battery administered in this sub-trial. The cognitive domain was a null result, consistent with the mixed prior literature on testosterone and cognition.

Cardiovascular Trial: This sub-trial found that testosterone therapy was associated with a statistically significant increase in coronary artery noncalcified plaque volume -- a measure of atherosclerotic plaque -- compared to placebo. The clinical significance of this finding was debated. The TTrials cardiovascular sub-trial enrolled a relatively small number of men (approximately 170) and used noncalcified plaque volume as a surrogate endpoint rather than clinical cardiovascular events. The cardiovascular sub-trial result contributed to the urgency of conducting the TRAVERSE trial.

Lessons from the TTrials: What They Did and Did Not Establish

The TTrials established several findings with high confidence. Testosterone therapy in older men with genuinely low testosterone improves sexual function. It increases bone density and estimated bone strength. It corrects unexplained anemia at rates substantially better than placebo. It modestly improves walking distance. It does not improve vitality or cognitive function.

What the TTrials did not establish was equally important. They studied a specific population -- men aged 65 and older with confirmed low testosterone and symptoms across multiple domains -- and their results may not apply directly to younger men, to men with less severe testosterone deficiency, or to men with different clinical profiles.

The TTrials' Legacy in Clinical Practice

The TTrials findings were incorporated into updated clinical guidelines from the Endocrine Society (2018) and the American Urological Association. They established a more rigorous evidentiary basis for the specific clinical benefits of testosterone therapy in older men -- benefits that had been asserted in prior smaller trials but had not been demonstrated with adequate statistical power in a well-designed randomized trial.

The TTrials remain the most comprehensive assessment of testosterone therapy outcomes across multiple domains in a single well-characterized population. They set the methodological standard that TRAVERSE later extended to the cardiovascular safety question.

Understanding Your Testosterone Today

The TTrials established what testosterone therapy can and cannot be expected to achieve in older men with confirmed hypogonadism. Sexual function improvement and bone density benefit are well-supported by the evidence. These findings inform how licensed clinical providers discuss testosterone therapy with patients today.

Keen Meds connects you with licensed clinical providers for a telehealth evaluation and lab review. If your testosterone is clinically low, you may qualify for a prescription for Testosterone Spray Rx -- a needle-free transdermal testosterone program.