Testosterone Optimization in Men: What the Evidence Actually Supports

Testosterone replacement therapy sits at an unusual intersection of legitimate medicine and marketing-driven hype. Separating signal from noise requires going back to the primary evidence — and understanding why the picture is more nuanced than either enthusiasts or critics suggest.

This article summarizes the current evidence base for testosterone therapy in adult men. It is educational information, not medical advice. Testosterone therapy requires clinician evaluation, confirmed laboratory values on at least two separate morning draws, and ongoing monitoring — it is not a supplement you self-prescribe.

What "low testosterone" actually means clinically

Hypogonadism is the formal clinical diagnosis: consistently low serum total testosterone paired with signs or symptoms attributable to deficiency. The Endocrine Society clinical practice guidelines (most recently updated in 2018) recommend against diagnosing hypogonadism based on symptoms alone or on a single borderline lab result. Total testosterone below approximately 300 ng/dL on two morning measurements, in the context of symptoms, meets the biochemical threshold — though labs use slightly different reference ranges, and free testosterone measurement matters when sex hormone–binding globulin (SHBG) is abnormal.

Symptoms associated with low testosterone include reduced libido, erectile dysfunction, decreased energy, loss of lean mass, increased fat mass, low mood, and reduced bone density. The challenge is that most of these are nonspecific — they also occur with sleep apnea, depression, obesity, hypothyroidism, and normal aging — which is why the workup matters before initiating treatment.

The Testosterone Trials (TTrials): the landmark evidence

The most rigorous dataset comes from the Testosterone Trials (TTrials), a coordinated set of seven double-blind, placebo-controlled trials conducted across 12 U.S. sites and published in a series of papers beginning in 2016 in the New England Journal of Medicine and JAMA Internal Medicine. The TTrials enrolled approximately 790 men aged 65 and older with confirmed low testosterone (below 275 ng/dL) and age-related symptoms.

Key findings:

• Sexual function: Testosterone improved self-reported sexual desire, activity, and erectile function versus placebo — this was the strongest and most consistent positive signal.
• Physical function: Modest improvement in walking distance (6-minute walk test) and self-reported vitality; statistically significant but clinically modest.
• Bone density: Volumetric bone mineral density increased, particularly at the spine — a meaningful finding given fracture risk in older men.
• Mood and cognition: Mixed results; no significant benefit for cognitive function; slight benefit for depressive symptoms in one sub-trial.
• Cardiovascular signal: A higher rate of coronary artery plaque progression (measured by CT angiography) was observed in the testosterone group. This was not powered to assess hard cardiovascular endpoints (MI, stroke), but it prompted continued caution.

The TTrials were conducted in older men with unequivocal hypogonadism. Extrapolating findings to younger men with low-normal testosterone or to men without confirmed deficiency is not supported by this evidence.

Formulations and practical pharmacology

Approved delivery routes include transdermal gels and solutions, intramuscular injections (testosterone cypionate or enanthate), subcutaneous injections, transdermal patches, and subcutaneous pellets. Each has different pharmacokinetic profiles:

• Injections produce supraphysiologic peaks followed by troughs, which some patients notice as mood or energy fluctuations.
• Daily gels and solutions produce steadier levels but carry a transfer risk to partners and children.
• Pellets are inserted every 3–6 months; dose adjustment requires a new procedure.

Hematocrit monitoring is mandatory on all formulations. Testosterone stimulates erythropoiesis; hematocrit above 54% substantially increases thrombotic risk and typically requires dose reduction, therapeutic phlebotomy, or treatment discontinuation.

Real risks that are often understated

• Erythrocytosis: The most common and dose-dependent adverse effect. Prevalence in treated men ranges from roughly 5–25% depending on formulation and dose.
• Testicular atrophy and infertility: Exogenous testosterone suppresses the hypothalamic–pituitary–gonadal axis, dramatically reducing intratesticular testosterone and spermatogenesis. This effect is not automatically reversible and is a critical discussion point for men who want future fertility. Gonadotropin-based regimens (hCG ± FSH) are used to preserve or restore fertility in this setting.
• Sleep apnea exacerbation: Testosterone worsens obstructive sleep apnea. Screening before initiation is appropriate; untreated severe sleep apnea is a relative contraindication.
• Prostate considerations: Testosterone therapy is contraindicated in men with known or suspected prostate cancer. It does not appear to initiate prostate cancer in men without it, but it can stimulate growth in existing disease. PSA monitoring is standard.
• Cardiovascular risk: Remains incompletely characterized. A large 2023 randomized trial (the TRAVERSE trial, published in the New England Journal of Medicine) found no significant increase in major adverse cardiovascular events in men with hypogonadism and elevated cardiovascular risk — a reassuring but not fully exonerating finding. Men with recent MI or stroke were excluded.

Who is the appropriate candidate?

The Endocrine Society guidelines and the American Urological Association both frame therapy as appropriate for men with:

1. Confirmed biochemical hypogonadism (two low morning total testosterone values)
2. Attributable symptoms that affect quality of life
3. No contraindications (active prostate cancer, hematocrit >54%, severe untreated sleep apnea, desire for near-term fertility without fertility-preserving protocol, recent major cardiovascular event)

The guidelines explicitly do not recommend testosterone therapy in men with age-related decline alone ("andropause") in the absence of true hypogonadism, or in men whose low testosterone is secondary to obesity or sleep apnea that has not been treated — because addressing the underlying cause often normalizes testosterone without exogenous therapy.

Key takeaways

• Testosterone therapy has well-supported benefits for sexual function, bone density, and body composition in men with confirmed biochemical hypogonadism — not in men with low-normal levels alone.
• The TTrials (2016–2018, NEJM and JAMA Internal Medicine) represent the highest-quality RCT evidence and inform current guidelines.
• Erythrocytosis, infertility, and prostate/cardiovascular considerations are real risks requiring regular monitoring.
• The TRAVERSE trial (2023, NEJM) provides partial cardiovascular reassurance but does not eliminate concern for all patient subgroups.
• Treatment decisions require confirmed labs, symptom assessment, contraindication screening, and ongoing monitoring — this is a clinician-supervised therapy, not a wellness supplement.

References

1. Endocrine Society Clinical Practice Guideline: Testosterone Therapy in Men with Hypogonadism (2018)
2. Snyder PJ et al. Effects of Testosterone Treatment in Older Men (TTrials sexual function trial). New England Journal of Medicine, 2016
3. Budoff MJ et al. Testosterone Treatment and Coronary Artery Plaque Volume (TTrials cardiovascular sub-trial). JAMA Internal Medicine, 2017
4. Bhasin S et al. Testosterone Therapy in Men with Hypogonadism — Endocrine Society Guidelines. Journal of Clinical Endocrinology & Metabolism, 2018
5. Lincoff AM et al. Testosterone Replacement Therapy and Cardiovascular Events (TRAVERSE Trial). New England Journal of Medicine, 2023
6. American Urological Association: Evaluation and Management of Testosterone Deficiency Guidelines (2018, amended 2022)