Benefits of Testosterone Replacement Therapy: What the Trials Measured

Ashley Harwyn, PA-C, ABAAHP  |  Published July 14, 2025  |  Last updated October 6, 2026  |  17 min read

Two large placebo-controlled trials measured what testosterone does for men with low levels. Here is what improved, what did not, and what to know about your heart.

This guide goes outcome by outcome through two large trials that measured them against a placebo: the Testosterone Trials (the T Trials) in men 65 and older, and TRAVERSE, which followed more than 5,000 men for close to three years.[2][4] We also cover what did not improve, what to watch on the heart side, and what has to be true before any of these benefits apply to you.

• In placebo-controlled trials, testosterone improved sexual activity and sexual desire in men with low levels. Erectile function improved in the T Trials but not in TRAVERSE.[2][5]
• Mood improved slightly, and TRAVERSE found a modest gain in energy. Neither trial found better memory or thinking, and TRAVERSE found no better sleep quality.[2][6]
• Anemia corrected in 41.0% of anemic men on testosterone versus 27.5% on placebo at six months in TRAVERSE.[7]
• Bone density rose in the T Trials, yet clinical fractures were more common on testosterone than placebo in TRAVERSE (3.50% versus 2.46%).[3][8]
• Major heart events were not higher on testosterone in TRAVERSE (7.0% versus 7.3%), but atrial fibrillation, acute kidney injury, and pulmonary embolism were more frequent.[4]
• These results apply to men with two low morning testosterone levels and symptoms. They do not show that testosterone helps men whose levels are normal.[1][9]

Which studies actually show what testosterone does?

Two trials carry most of the weight, and both were randomized, double blind, and compared testosterone gel with a placebo gel. A placebo comparison separates the effect of the hormone from the effect of expecting to feel better, so in this guide a benefit counts only when the testosterone group beat the placebo group.

The T Trials enrolled 790 men aged 65 or older whose testosterone was below 275 ng/dL and who had symptoms suggesting low testosterone. Each man took part in one or more of three trials (sexual function, physical function, vitality) for one year, and other trials in the program looked at bone, anemia, thinking, and coronary plaque.[2][3] Of 51,085 men who initially contacted study sites, only 1.5% of those who expressed interest were enrolled, mainly because their testosterone was not low enough.[3]

TRAVERSE was larger and longer. It enrolled 5,246 men aged 45 to 80 who had symptoms of low testosterone, two fasting testosterone levels under 300 ng/dL, and either existing heart disease or a high risk of it. The mean time on treatment was 21.7 months and mean follow-up was 33.0 months.[4] Its main job was heart safety, but separate studies nested inside it measured sexual function, mood, anemia, and fractures.[5][6][7][8]

One limit applies to both. Both enrolled only men with low testosterone, neither enrolled men younger than 45, and both aimed for levels in the normal range. The T Trials raised levels to the mid-normal range for men 19 to 40,[2] and TRAVERSE adjusted the gel to keep levels between 350 and 750 ng/dL.[4] What follows describes treatment to a normal level, not more.

Does testosterone improve sex drive and erections?

Both trials found a sexual benefit, with one important split. In the T Trials, raising testosterone to the mid-normal range for young men significantly increased sexual activity, sexual desire, and erectile function compared with placebo.[2] The authors described the gain in sexual function as moderate.[2]

TRAVERSE asked the same question over a longer stretch in 1,161 men who reported low libido. Testosterone raised sexual activity by about half an act per day more than placebo at six months (0.49), held a similar gain at 12 months, and kept the effect at 24 months. Sexual desire and overall low-testosterone symptoms improved as well. Erectile function did not improve compared with placebo.[5]

So the two trials agree on desire and activity and disagree on erections. Erections also have many possible causes. The National Institute of Diabetes and Digestive and Kidney Diseases lists diabetes, heart and blood vessel diseases, high blood pressure, nerve damage, hormone issues such as low testosterone, many common medicines, and anxiety, depression, or stress, and notes that erectile dysfunction “may be a symptom of another health problem.”[10] Our post on erectile dysfunction and heart disease covers the blood vessel side.

The American Urological Association lists improvement in “erectile function, low sex drive” among the outcomes patients may see, phrased as possible rather than promised.[1] If erections are the main concern and libido is fine, ask at your visit whether a broader sexual dysfunction evaluation fits your situation.

Can TRT help mood, energy, and focus?

In the T Trials, men on testosterone reported slightly better mood and slightly fewer depressive symptoms than men on placebo. Vitality, measured on a standard fatigue scale, showed no significant benefit.[2] So the trial built specifically to test vitality in older men did not find a benefit.

TRAVERSE looked again in 5,204 men, and 2,643 of them (50.8%) had significant depressive symptoms at the start. Across the whole group and in that subgroup, testosterone produced “modest but significantly greater improvements in mood and energy” than placebo, but not in cognition or sleep quality.[6] In the small group with a formally diagnosed low-grade persistent depression (49 men), there was no significant difference on any measure, possibly because the group was too small to show one.[6]

Thinking and memory did not move. The T Trials cognitive study found no change in verbal memory, visual memory, spatial ability, or global cognitive function.[3] The AUA states plainly that the evidence is inconclusive on whether testosterone improves “cognitive function, measures of diabetes, energy, fatigue, lipid profiles, and quality of life measures.”[1]

What should you take from that? In these trials the average gains in mood were slight to modest, the AUA calls the evidence on energy inconclusive,[1][2][6] and in men with diagnosed low-grade persistent depression there was no significant difference from placebo.[6] If low mood is the main problem, you can ask about a mental health evaluation as well.

What does testosterone do for bone, anemia, and strength?

Testosterone deficiency causes mild anemia, according to the TRAVERSE anemia study, which tested whether treatment corrects it. Among 815 men who started out anemic (hemoglobin below 12.7 g/dL), anemia corrected in 41.0% on testosterone versus 27.5% on placebo at six months, and in 45.0% versus 33.9% at 12 months. Among men who were not anemic, fewer on testosterone developed anemia. Changes in hemoglobin tracked with changes in energy.[7]

The same effect has a downside. In the T Trials, 7 men on testosterone and none on placebo reached a hemoglobin of 17.5 g/dL or higher.[3] The AUA directs clinicians to measure hemoglobin and hematocrit before offering testosterone and to inform patients of the increased risk of polycythemia, meaning too many red blood cells.[1]

Bone is where the two trials point in different directions. In the T Trials, testosterone slightly increased bone density and estimated bone strength, more at the spine than the hip, gains the review author called similar in size to bisphosphonate therapy in women with osteoporosis.[3] Then TRAVERSE counted actual broken bones. After a median of 3.19 years, a clinical fracture occurred in 91 men on testosterone (3.50%) and 64 on placebo (2.46%), a hazard ratio of 1.43.[8]

The authors concluded that testosterone “did not result in a lower incidence of clinical fracture than placebo,” with fractures numerically higher on testosterone.[8] The bone density and fracture results come from different trials, but only TRAVERSE counted broken bones. If you have osteoporosis, these results are a reason to discuss fracture prevention separately rather than count on testosterone for it.

Walking results were mixed. In the T Trials, the physical function trial alone showed no significant gain in walking distance. Pooling all three trials, 20.5% of men on testosterone versus 12.6% on placebo improved their six-minute walk by at least 50 meters.[2] Lean body mass is on the AUA list of possible improvements.[1] If body composition is one of your goals, body composition analysis is one way to measure it.

Which TRT benefits are proven, and which are not?

Here is the scorecard, drawn from the two placebo-controlled trials and the AUA guideline. A “yes” means the testosterone group beat placebo. A “no” means it did not, or went the other way.

Read across the rows and a pattern shows up. The benefits found in both trials are in sexual desire and activity, mood, and anemia. Thinking did not improve in either trial, energy improved in only one, and fractures were more frequent on testosterone.

Because the trials measured specific outcomes, it helps to name the symptoms you hope will change before you start, so they can be checked at follow-up, which is the step the AUA uses to decide whether to continue.[1]

Is testosterone therapy safe for your heart?

Before TRAVERSE, the cardiovascular safety of testosterone in middle-aged and older men with low levels had not been determined.[4] A major heart event (cardiovascular death, nonfatal heart attack, or nonfatal stroke) occurred in 182 men on testosterone (7.0%) and 190 on placebo (7.3%), a hazard ratio of 0.96 with a 95% confidence interval of 0.78 to 1.17.[4] The authors concluded that testosterone was noninferior to placebo for these events in men who already had heart disease or a high risk of it.[4]

TRAVERSE also found a higher incidence of atrial fibrillation, acute kidney injury, and pulmonary embolism in the testosterone group.[4] If you have a heart rhythm problem, kidney disease, or a history of blood clots, raise it before starting.

Earlier, a T Trials substudy found that testosterone slightly increased noncalcified and total coronary plaque volume, but not coronary calcium score.[3] The review author noted that the clinical significance of this increase is not clear.[3]

The FDA acted on TRAVERSE on February 28, 2025. It removed language from the boxed warning related to an increased risk of adverse cardiovascular outcomes, and, based on blood pressure monitoring studies, required a new warning about increased blood pressure for products that did not already carry one.[9] It also kept the “Limitation of Use” language for age-related low testosterone.[9] The AUA adds a timing rule: testosterone should not be started for three to six months in men with a history of a cardiovascular event.[1] Cardiovascular history is part of the conversation before any prescription on our TRT page, and our cardiac health service is there if you want a closer look.

Wondering which of these benefits fits your symptoms? Call 843-981-0870. The assessment starts with your history, then two early morning draws on separate days, then a conversation with Ashley about what the evidence does and does not support, before any prescription.

Who is likely to benefit, and what comes first?

Every benefit above was measured in men with low testosterone confirmed on more than one blood test and real symptoms. The AUA guideline makes the diagnosis only after two total testosterone measurements on separate occasions, both drawn in the early morning, and calls a level below 300 ng/dL a reasonable cut-off.[1] The FDA approves testosterone “solely for use in men who lack or have low testosterone levels in conjunction with an associated medical condition.”[9]

That has a practical meaning. If your morning levels are normal, these trials do not tell you what testosterone would do for you, because they did not enroll men like you. Many of the ten signs of low testosterone overlap with other causes worth excluding first, and full panel lab testing is one place to start.

The AUA lists three checks before a prescription. First, fertility: the long-term impact of testosterone on sperm production should be discussed with men interested in future fertility, and it “should not be prescribed to men who are currently trying to conceive.”[1] Second, hemoglobin and hematocrit, because of the red cell effect described above. Third, PSA in men over 40, to exclude a prostate cancer diagnosis.[1] The AUA asks clinicians to tell patients there is no evidence linking testosterone therapy to the development of prostate cancer.[1]

Then comes monitoring. The AUA calls for testosterone levels every 6 to 12 months on treatment,[1] and our TRT page lists blood pressure among the things monitored, given the FDA's 2025 blood pressure warning.[9] Follow-up is also where you ask whether the symptoms you came in for actually changed. The AUA advises discussing stopping therapy three to six months in if levels are normal but symptoms have not improved, and it recommends adjusting the dose to reach the middle third of the normal range rather than above it.[1] Ashley Harwyn, PA-C sees men for this in Mount Pleasant and at The Longevity Club in downtown Charleston.

Ashley Harwyn, PA-C PA-C, ABAAHP · Founder, Solcara Health Online

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