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Testosterone — the primary androgen; testosterone-replacement therapy (TRT)
The primary male androgen and a prescription medicine with US FDA-approved products for specified causes of male hypogonadism, and a Schedule III controlled substance in the US. For men with genuinely low testosterone, randomized trials show real benefits: the Testosterone Trials (TTrials) improved sexual function, mood, anemia and bone density in older hypogonadal men, and the large TRAVERSE trial found TRT non-inferior to placebo for major cardiac events. But those benefits were modest and indication-specific, NOT a longevity or anti-aging result. It is prescription-only in Germany and Austria. Non-medical, supraphysiologic and 'anti-aging' use is not established as safe or effective for longevity and carries serious harms — erythrocytosis, suppressed sperm production/fertility, cardiovascular and psychiatric risk. This is a harm-reduction reference, not a recommendation, and testosterone is NOT a dietary supplement.
Prescription medication — not a dietary supplement
Testosterone (TRT) is a prescription (or investigational) drug, not a supplement. It is included here for reference because people research and discuss it (often used off-label) — not as a recommendation. Take it only under a qualified clinician's supervision and only as prescribed; do not source it from grey-market vendors, where identity, purity, and dosing are unverified. The evidence below reflects its clinical trials.
What the evidence says
Testosterone (TRT) doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1968–2026 with a typical study size of 55,593 participants.
Based on 702 studies · 106 meta-analyses · 537 RCTs · 55,864 total participants
Confidence
High confidenceBy outcome
For diagnosed male hypogonadism the evidence is real and randomized: the Testosterone Trials improved sexual function, mood, anemia and bone density, an RCT meta-analysis found gains in lean mass and hip bone density at 6 months, and the large TRAVERSE trial found TRT non-inferior to placebo for major adverse cardiac events. But those benefits are modest and indication-specific — NOT a longevity outcome — and testosterone is a US Schedule III controlled substance and a prescription-only medicine in Germany and Austria that even at therapeutic doses causes erythrocytosis and suppresses sperm production, with the earlier TOM trial and an observational MI signal as genuine cardiovascular counter-evidence, and serious cardiomyopathy/dyslipidemia/dependence risk in supraphysiologic non-medical use. Effective where indicated; legally controlled and genuinely harmful when misused.
559 randomised trials
90% were about Testosterone (TRT) in an audit of 50 of them
Every randomised or controlled trial of Testosterone (TRT) indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Sep 2026
14 trials ongoing or recruiting · 18 completed on ClinicalTrials.gov
11 of the completed trials have posted results
Registered trials show research momentum for Testosterone (TRT), not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Nov 2026
Testosterone is the primary androgen — the steroid hormone, made chiefly by the testicular Leydig cells under pituitary LH control, that drives male sexual development, libido, erythropoiesis, muscle and bone mass, and mood.
Testosterone-replacement therapy (TRT) is the medical replacement of that hormone in men with diagnosed hypogonadism: biochemically low testosterone (typically confirmed on repeat morning measurements) plus consistent symptoms. In that population the evidence is genuinely strong and randomized.
The coordinated Testosterone Trials (TTrials) in symptomatic men 65 and older with unequivocally low testosterone showed that one year of gel raised testosterone to mid-normal young-male levels and improved sexual activity and desire, modestly improved mood and depressive symptoms, corrected anemia (both unexplained and from known causes), and increased volumetric bone mineral density and estimated bone strength, but showed no benefit for vitality or walking distance.
The large, cardiovascular-safety-powered TRAVERSE trial (Lincoff 2023, NEJM) then randomized middle-aged and older hypogonadal men with high cardiovascular risk and found transdermal testosterone non-inferior to placebo for major adverse cardiac events (cardiovascular death, nonfatal MI, nonfatal stroke) — reassuring on the central cardiovascular-safety question that had dogged the field, though it flagged more atrial fibrillation, acute kidney injury, and pulmonary embolism.
A meta-analysis of randomized trials found 6 months of TRT increased hip bone density and lean mass, while its effects on fat mass and handgrip strength were not significant and no musculoskeletal effect was significant at 12 months. That is the honest, real, indication-bounded case for TRT.
The other side is why it is described for harm reduction rather than recommended. Testosterone is a Schedule III controlled substance in the United States and a prescription-only medicine in Germany and Austria. Laws on supply, possession, import and use depend on the country and circumstances.
Products from unverified sources may have unreliable identity, strength or quality. Second, the proven benefits are narrow and were never longevity outcomes — the TTrials were modest, time-limited (one year), and explicitly not a healthspan or lifespan trial, so framing TRT as 'anti-aging' overstates the evidence.
Third, the harms are real and dose-dependent.
Even at therapeutic doses, testosterone commonly causes erythrocytosis/polycythemia (a rise in hematocrit that raises clot and stroke risk) and suppresses the hypothalamic-pituitary-testicular axis, shrinking the testes and dropping endogenous sperm production — experimental male hormonal contraception relies on this suppression, using an androgen with a progestin.
Testosterone can suppress sperm production. If you want to father children now or in the future, discuss alternatives with a fertility specialist before starting. Testosterone alone should not be prescribed when current or future fertility is desired.
If you already take prescribed testosterone, discuss your plans promptly with your prescriber and a fertility specialist before changing treatment.
The earlier TOM trial (Basaria 2010, NEJM) in frail older men with mobility limitations was stopped early after more cardiovascular adverse events in the testosterone arm, and a large observational cohort (Finkle 2014) found an elevated rate of non-fatal myocardial infarction in the 90 days after a first testosterone prescription, especially in older men — the counter-evidence that TRAVERSE later tempered but did not erase.
Prostate considerations (TRT does not appear to cause prostate cancer but can raise PSA and is avoided in active prostate cancer) require monitoring.
And supraphysiologic, non-medical anabolic-steroid use — far above replacement doses — is a different and more dangerous activity, associated with cardiomyopathy and impaired cardiac function, adverse lipid changes (suppressed HDL), dependence, and mood/psychiatric effects.
The score reflects this split: real, randomized benefit for diagnosed hypogonadism (sexual function, mood, anemia, bone, body composition, and reassuring TRAVERSE cardiovascular safety) against its US controlled-substance status, an unproven longevity claim, and documented hematologic, fertility, cardiovascular, and psychiatric harms — especially with non-medical or supraphysiologic use.
Testosterone is a prescription medicine and, in the US, a controlled substance. It is not a dietary supplement and has no established longevity indication.
Testosterone binds the intracellular androgen receptor, which translocates to the nucleus and drives androgen-responsive gene transcription — the basis for its effects on muscle and bone anabolism, libido, mood, and erythropoiesis.
Testosterone is converted by aromatase to estradiol (important for bone, mood, and libido) and by 5α-reductase to the more potent androgen dihydrotestosterone (DHT). Many testosterone effects are actually mediated by these metabolites, and the estradiol it produces is part of why it supports bone.
Exogenous testosterone signals the hypothalamus and pituitary that levels are sufficient, suppressing GnRH, LH and FSH — which shuts down endogenous testosterone and sperm production (testicular atrophy, infertility). It also stimulates erythropoiesis, raising hematocrit; the same axis suppression and red-cell rise are the core therapeutic-dose harms.
How Testosterone (TRT) works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
This is the indication the RCT evidence supports. Confirm with repeat morning testosterone, treat under a clinician, and monitor hematocrit and PSA. Benefits are real but modest — not a performance or longevity intervention.
Testosterone can suppress sperm production. If you want to father children now or in the future, discuss alternatives with a fertility specialist before starting. Testosterone alone should not be prescribed when current or future fertility is desired. If you already take prescribed testosterone, discuss your plans promptly with your prescriber and a fertility specialist before changing treatment.
TRAVERSE was reassuring on major cardiac events but flagged atrial fibrillation, AKI and pulmonary embolism, and the TOM trial stopped early for cardiovascular events in frail men. Assess cardiovascular risk carefully before and during therapy.
Avoid — it is a US Schedule III controlled substance and prescription-only in Germany and Austria, the 'anti-aging' benefit is unproven, and supraphysiologic use carries cardiomyopathy, lipid, fertility, hematologic and psychiatric harm.
Contraindicated in active prostate cancer; TRT can raise PSA. PSA and prostate exam should be checked before and during therapy.
Testosterone can potentiate anticoagulant effect and raise bleeding risk; INR and dosing need monitoring. The erythrocytosis it causes also independently affects clot risk.
Stacking androgenic agents (common in non-medical use) compounds erythrocytosis, lipid and HPTA effects; aromatase inhibitors are sometimes added to manage estradiol but can over-suppress it and harm bone and lipids. Unvalidated and risky outside clinical care.
Testosterone can improve insulin sensitivity and lower glucose, which may require adjustment of diabetes medication to avoid hypoglycemia.
Concurrent corticosteroids can increase fluid retention/edema, especially in patients with cardiac or renal disease.
Tip: A dose-dependent rise in red cells that raises clot/stroke risk. The US label (AndroGel 1.62%, section 5.2) says to check hematocrit before starting, again 3 to 6 months after starting and then annually, and to stop treatment if it becomes elevated until it falls to an acceptable level. In the Testosterone Trials, six men who were not anemic at baseline reached hemoglobin above 17.5 g/dL. Higher with injectable than transdermal forms.
Tip: Exogenous testosterone shuts down the HPTA and spermatogenesis. The US labels state that large doses of exogenous androgens may suppress spermatogenesis and lower sperm count (AndroGel 1.62%, section 5.8). In a WHO trial, testosterone enanthate 200 mg weekly made 65% of healthy men azoospermic within 6 months. If you want to father children now or in the future, discuss alternatives with a fertility specialist before starting. If you already take prescribed testosterone, discuss your plans promptly with your prescriber and a fertility specialist before changing treatment. Recovery after stopping is variable and can take months.
Tip: Flagged as more frequent on testosterone than placebo in TRAVERSE. Chest pain, sudden breathlessness, coughing up blood or collapse: call emergency services now. Sudden swelling of one leg or a warm, painful calf: get urgent medical assessment today. Report palpitations to the prescriber. Cardiovascular risk should be assessed before and during therapy.
Tip: Non-medical anabolic-steroid doses are associated with impaired cardiac function/cardiomyopathy and suppressed HDL cholesterol. There is no safe self-directed high-dose regimen; this library does not provide one.
Tip: Modest mood effects can occur at therapeutic doses; supraphysiologic use is linked to irritability/aggression, mood disorders, and androgen dependence. Monitor mood and avoid non-medical escalation.
Tip: Androgenic and aromatization-related effects; usually manageable with dose adjustment under a clinician.
Testosterone (TRT) has an evidence score of 5.6/10 — moderate evidence based on 702 indexed studies, including 2 meta-analyses. The primary male androgen and a prescription medicine with US FDA-approved products for specified causes of male hypogonadism, and a Schedule III controlled substance in the US. For men with genuinely low testosterone, randomized trials show real benefits: the Testosterone Trials (TTrials) improved sexual function, mood, anemia and bone density in older hypogonadal men, and the large TRAVERSE trial found TRT non-inferior to placebo for major cardiac events. But those benefits were modest and indication-specific, NOT a longevity or anti-aging result. It is prescription-only in Germany and Austria. Non-medical, supraphysiologic and 'anti-aging' use is not established as safe or effective for longevity and carries serious harms — erythrocytosis, suppressed sperm production/fertility, cardiovascular and psychiatric risk. This is a harm-reduction reference, not a recommendation, and testosterone is NOT a dietary supplement. Representative study: PMID 37164187.
Dosing for Testosterone (TRT): Prescription-only and clinician-directed — this is a controlled substance, NOT a self-administered supplement, and we do not provide a non-medical dosing protocol. For context only: TRT for diagnosed hypogonadism is titrated to a mid-normal testosterone level. Intramuscular testosterone esters (cypionate/enanthate) are commonly dosed around 50–100 mg weekly (or ~100–200 mg every 2 weeks); long-acting testosterone undecanoate is dosed less frequently. Transdermal gels (~50–100 mg/day applied) and subcutaneous injection are alternative routes. Supraphysiologic anabolic-steroid doses are far higher and dangerous — not a regimen this library endorses. Individual needs vary, so check the right dose for you with a healthcare provider.
Timing is flexible for Testosterone (TRT) — consistent daily use matters more than the time of day. There is no validated supplement timing — TRT is a prescription drug titrated by a clinician to a target serum testosterone (and monitored hematocrit/PSA), not a fixed self-dosing schedule.
Testosterone (TRT) should be used with caution — talk to a healthcare provider before taking it. Reported side effects include risks of supraphysiological testosterone, erythrocytosis / polycythemia (raised hematocrit), suppressed sperm production / infertility & testicular atrophy. How often they occur is not established for all of them. Use caution if any of these apply to you: Use without a prescription / without medical supervision — testosterone is a US Schedule III controlled substance and prescription-only in Germany and Austria; Active prostate cancer or active breast cancer in men; Untreated severe erythrocytosis / hematocrit above the safe threshold.
What side effects does Testosterone (TRT) have?Don't take this if…
Enclomiphene
Too few graded studiesThe trans-isomer of clomiphene — a selective estrogen receptor modulator (SERM) used investigationally as a testosterone therapy. By blocking estrogen feedback at the hypothalamus it raises LH, FSH, and endogenous testosterone. Honest appraisal: Phase-2/3 RCTs show it raises testosterone — but it is NOT FDA-approved (Androxal failed to gain approval) and is compounded, and there are NO long-term hard-outcome trials (cardiovascular, bone, mortality).
Zinc
Likely helpsInvolved in 300+ enzymatic reactions — supports immune defense, testosterone production, wound healing, and sleep quality.
Ashwagandha
Likely helpsReduces cortisol and anxiety while improving sleep quality and physical recovery in stressed adults.
Tongkat Ali
Too few graded studiesSoutheast Asian herb with moderate RCT evidence for supporting testosterone, reducing stress/cortisol, and improving fatigue and quality of life — strongest in older or hypogonadal men.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 702 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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