Testosterone is often sold as a muscle hormone, but its receptors sit in the brain, the blood-forming marrow, bone, fat and blood vessels. Trials have looked at it for far more than sex drive. Some results are encouraging, some are empty, and a few point to risks. Here is what the randomized trials show, and what they do not.
Sex drive and sexual function
The Testosterone Trials enrolled 790 men aged 65 and older with low testosterone and symptoms. Over one year, testosterone gel gave a moderate improvement in sexual activity and desire compared with placebo, and a smaller improvement in erectile function scores. The effect was modest, and the authors noted that it tended to fade toward the end of the year.
The same trials found no benefit for vitality, a measure of energy and wellbeing, and no clear gain in walking distance in the physical-function trial.
Blood and energy
Testosterone stimulates red blood cell production. In the Testosterone Trials, men with unexplained anemia were far more likely to show a clinically significant rise in hemoglobin than men on placebo: 54% versus 15% after one year. The same effect can push hematocrit too high, so our physicians measure it during treatment and pause therapy when it climbs.
Bone
In the bone substudy of the Testosterone Trials, one year of gel increased volumetric bone density and estimated bone strength compared with placebo, with the largest gains in the spine. Bone density is not the same as fracture risk, and the trial was not designed to count fractures. The later TRAVERSE fracture substudy, in a higher-risk group, found more fractures on testosterone, not fewer. That is covered in the second article.
Blood sugar
T4DM randomized 1,000 men aged 50 to 74 with impaired glucose tolerance or early type 2 diabetes, all enrolled in a weight-loss program, to testosterone undecanoate injections every three months or placebo, for two years. Diabetes developed in 21% of the placebo group (87 of 413) and 12% of the testosterone group (55 of 443), a 41% relative reduction. The authors caution that durability and long-term safety are not known, that weight loss remained the main driver, and that it is premature to treat men without low testosterone for this purpose.
Thinking and the coronary arteries
Two findings cut the other way. In the Testosterone Trials series, testosterone did not improve memory or other cognitive function in older men with low testosterone and memory complaints. Coronary artery plaque volume increased in the testosterone group, which is one reason the heart question gets its own article.
What this does not say
- Most of these trials studied men with low testosterone confirmed by repeat blood tests, followed for one to three years. They do not describe men with normal levels, and they do not describe lifelong treatment.
- The trials used brand-name or standard products at the studied doses. Our compounded or generic versions were not the products studied.
- Averages are not predictions. Sex drive, anemia and blood sugar change in some men and not in others, and the average gains are modest.
How we use this
Our physicians treat men with symptoms and consistently low testosterone, confirmed by repeat testing, and look for the cause first. The benefits in sexual function, blood counts and blood sugar are real in the trials but modest, and they come with monitoring.
We do not use these trials to promise a longer life. We use them to set honest expectations, and we measure the things we say we will watch.
Explore weight loss treatmentsSources
- 1.Snyder PJ et al. Effects of Testosterone Treatment in Older Men (Testosterone Trials). N Engl J Med 2016;374:611-624. NEJM
- 2.Roy CN et al. Association of Testosterone Levels With Anemia in Older Men: A Controlled Clinical Trial. JAMA Intern Med 2017;177:480-490. JAMA Internal Medicine
- 3.Budoff MJ et al. Testosterone Treatment and Coronary Artery Plaque Volume in Older Men With Low Testosterone. JAMA 2017;317:708-716. JAMA
- 4.Resnick SM et al. Testosterone Treatment and Cognitive Function in Older Men With Low Testosterone and Age-Associated Memory Impairment. JAMA 2017;317:717-727. JAMA
- 5.Wittert G et al. Testosterone treatment to prevent or revert type 2 diabetes in men enrolled in a lifestyle programme (T4DM): a randomised, double-blind, placebo-controlled, 2-year, phase 3b trial. Lancet Diabetes Endocrinol 2021;9:32-45. The Lancet Diabetes & Endocrinology
- 6.Snyder PJ et al. Lessons From the Testosterone Trials. Endocr Rev 2018;39:369-386. Endocrine Reviews
- 7.Bhasin S et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2018;103:1715-1744. JCEM