Preface

The core evidence-based message: testosterone therapy has a robust, guideline-supported role only in men with confirmed, symptomatic organic hypogonadism (biochemically low fasting morning testosterone on ≥2 occasions plus consistent symptoms), where it reliably improves libido, sexual activity, lean mass, bone mineral density, and corrects anaemia.[1][2] The large TRAVERSE RCT (n=5198) established short-to-medium-term cardiovascular non-inferiority versus placebo (HR 0.96, 95% CI 0.78–1.17).[3][4] There is no high-quality evidence that TRT extends lifespan, prevents cardiovascular events, or acts as a “restorative” anti-ageing hormone, and using it purely to push testosterone into the upper range in eugonadal men for longevity is off-label, unproven, and potentially harmful.[5][6] Long-term (>3 year) safety data remain absent.[7][8]

1. Scope

– Covered: Assessment, patient selection, initiation, dosing, monitoring and safety of testosterone therapy in adult men within a UK longevity/preventive-medicine setting, working alongside NHS primary/secondary care.

– Not covered: Female/menopausal testosterone use; fertility-preserving regimens (hCG, SERMs, aromatase inhibitors — noted only briefly); anabolic-androgenic steroid misuse for bodybuilding; paediatric/pubertal induction; selective androgen receptor modulators (SARMs), which remain experimental/research-only with no licensed longevity indication.[2]

– Framing: Content is adjunctive to conventional care. Where a man may have organic hypogonadism, NHS endocrinology/urology referral is appropriate rather than independent private initiation.

2. Background and pathophysiology

– Serum testosterone declines gradually with age (~1–2%/year from midlife), compounded by obesity, metabolic syndrome, medications and comorbidity. Much “low testosterone” in ageing men is functional (secondary, potentially reversible) rather than organic.[9][10]

– Biologically, testosterone acts via the androgen receptor in myonuclei, satellite cells, bone, CNS and erythroid precursors, driving anabolic effects on muscle and bone, erythropoiesis, libido and mood.[2][11]

– Mechanisms relevant to ageing (human evidence): increased lean body mass and reduced fat mass; increased volumetric/areal BMD and estimated bone strength; correction of unexplained anaemia; modest improvement in insulin sensitivity/glycaemia. These are surrogate/intermediate outcomes — improvements do not reliably translate into reduced fractures, falls, disability or mortality.[1][2][12]

– Observational signal: In UK Biobank, lower endogenous testosterone associated with higher all-cause mortality but not incident CVD; an IPD meta-analysis showed higher all-cause and CV mortality only below thresholds of ~7.4 nmol/L and ~5.3 nmol/L respectively. These are associations, not proof of causation or of treatment benefit.[8]

– Preclinical (clearly separated, low weight): Animal/in-vitro work suggests androgen effects on endothelial function, visceral fat and vascular tone, but also potentially adverse effects (thromboxane-mediated platelet aggregation, vascular smooth-muscle proliferation) — mechanistic plausibility only, not a basis for clinical claims.[5]

3. Evidence base and grading

Available evidence includes multiple RCTs, several IPD and aggregate meta-analyses, one large dedicated CV-safety RCT (TRAVERSE), the Testosterone Trials (TTrials), the T4DM diabetes-prevention RCT, and large prospective cohorts. GRADE-style certainty by outcome:

Outcome	Evidence & certainty (GRADE)	Direction	Strength of recommendation
Sexual function / libido	Moderate–High: consistent across TTrials + meta-analyses; some inconsistency for erectile dysfunction	Benefit in confirmed hypogonadism	Strong (offer) in symptomatic biochemical hypogonadism [1], [2]
Lean mass / BMD / body composition	Moderate: consistent RCT effect at 6 months; wanes/uncertain at 12 months; surrogate endpoints	Benefit	Conditional [2], [12]
Anaemia correction	Moderate: TTrials RCT	Benefit	Conditional [1], [2]
Type 2 diabetes prevention	Moderate: single large RCT (T4DM) on background lifestyle; ~40% relative reduction, but erythrocytosis in ~22%	Benefit + harm trade-off	Conditional / research-adjacent; lifestyle first [5], [6], [8]
MACE (cardiovascular safety)	Moderate: TRAVERSE non-inferiority + IPD/RCT meta-analyses, ≤3 yr only	Neutral (no excess)	Reassuring short–medium term; no benefit claim [3], [4], [7], [13]
Fractures, falls, disability, mobility	Low: underpowered; TRAVERSE showed increased clinical fractures	Uncertain / possible harm	Recommend against as an indication [2], [4]
All-cause mortality / longevity	Very low: no adequately powered trial; deaths few, high-risk excluded	Unproven	Only in research as a goal [7], [14]
VTE / pulmonary embolism	Moderate: increased PE in TRAVERSE; observational AF/VTE signals	Harm	Caution; contraindicated in thrombophilia [3], [4], [15]
Erythrocytosis	High: most reproducible adverse effect (17% vs 3.3%)	Harm	Monitor mandatorily [15]

– Key limitations across the base: heterogeneous populations/formulations, variable on-treatment levels, inconsistent event adjudication in older trials, short duration (indirectness and imprecision for long-term/longevity outcomes), and exclusion of highest-risk men (indirectness). Publication bias is plausible given historical industry involvement and direct-to-consumer marketing.[5][14]

4. Patient selection and indications

The evaluation and management algorithm below (JAMA 2026) operationalises appropriate selection — confirm low fasting morning testosterone, assess free testosterone if obesity/diabetes, measure LH/FSH, and treat reversible causes (especially obesity) before initiating therapy:

Figure 2 Algorithm for the Evaluation and Management of Male Hypogonadism

– Who may benefit (offer/consider):

– Men with symptoms of androgen deficiency (low libido, loss of morning erections, fatigue, reduced wellbeing) and fasting morning total testosterone below the reference range confirmed on ≥2 occasions; benefit is greatest when TT <6.9 nmol/L (200 ng/dL).[4]

– Primary hypogonadism (low TT, high LH/FSH): generally offer replacement irrespective of age.[9][10]

– Older men with confirmed hypogonadism and bothersome sexual symptoms or hypogonadism-related anaemia — conditional.[1]

– Clinical scenarios requiring caution/restraint:

– “Functional” hypogonadism from obesity/metabolic syndrome: lifestyle optimisation, weight loss and GLP-1/GIP agonists first — testosterone normalises in a majority after metabolic intervention/bariatric surgery. TRT here is second-line.[15][9]

– Athletic/performance-seeking eugonadal men: no longevity indication; use for performance is off-label and not supported.[2]

– Exclusion / high-risk (see §8).

– Regulatory/ethical status (UK): Testosterone products (e.g. Testogel/Tostran gel, Nebido/Sustanon injectable) are MHRA-licensed only for confirmed hypogonadism. Use to “optimise” levels in eugonadal men for anti-ageing is off-label, requires explicit documented informed consent, and should ideally sit within audit/registry frameworks. Mortality/longevity benefit should be treated as research-only.[8][14]

5. Assessment and baseline work-up

– History: sexual symptoms, energy/mood, fracture/falls history, VTE/thrombophilia, cardiovascular disease, fertility intentions, OSA symptoms, LUTS, medications (opioids, glucocorticoids, GnRH analogues). Consider validated symptom tools (e.g. ADAM) — sensitive but non-specific.[17]

– Examination: BMI/waist, testicular volume (Prader orchidometer; ≤12 cm³ suggests prepubertal-onset/Klinefelter), gynaecomastia, prostate (DRE where indicated), BP.[10]

– Baseline investigations:

– Total testosterone — fasting, 07:00–10:00, on two occasions; add calculated free testosterone/SHBG especially in obesity or diabetes.[10][4]

– LH, FSH (primary vs secondary); prolactin if LH low/low-normal ± MRI pituitary if indicated.[17][10]

– FBC/haematocrit — baseline HCT >48–50% is a contraindication.[17]

– PSA in men ≥40 years before initiation; DRE where indicated.[17][1]

– HbA1c, lipids, LFTs, U&E, ferritin/iron studies; 25-OH vitamin D (correct deficiency).[18]

– Consider BMD (DXA) if fracture risk/long-standing hypogonadism.[1]

– Risk stratification: integrate CV risk (QRISK), VTE/thrombophilia risk, prostate-cancer risk (age, family history, ethnicity, PSA), OSA and baseline haematocrit to weigh benefit vs harm.[4][10][1]

– Baseline documentation: symptom scores, two testosterone values, HCT, PSA, CV/VTE risk, and explicit consent regarding off-label use and unknown long-term/prostate/CV effects.[9]

6. Dosing regimens and practical implementation

Aim for mid-normal serum testosterone — not supraphysiological levels.[1]

– Transdermal gel (e.g. testosterone 1–2%): typically 40–80 mg/day, titrated to trough mid-normal levels; lower erythrocytosis risk than injectables; risk of transfer to women/children (skin contact precautions).[14][1]

– Long-acting IM testosterone undecanoate (Nebido 1000 mg): 1000 mg IM, repeat at 6 weeks, then every 10–14 weeks to trough mid-normal; stable levels, lower peaks.[1]

– Shorter-acting IM esters (e.g. Sustanon 250): every 2–3 weeks; higher peak-trough swings and greater erythrocytosis risk.[15][1]

– Titration: check level relative to formulation (trough for undecanoate; mid-interval for gels). Adjust to symptoms + mid-normal biochemistry, not to arbitrary “optimised” high targets.

– Fertility preservation: exogenous testosterone suppresses spermatogenesis; if fertility desired, do not use TRT — hCG ± FSH or SERMs are alternatives (specialist input).[19][1]

– Regimens requiring caution / not evidence-based: high-dose “optimisation” to top-of-range/supraphysiological levels, and SARMs — no robust human longevity data; avoid outside trials.[2]

7. Monitoring, safety and follow-up

– Monitoring plan:

– Symptoms/adverse effects at each review; BP (possible 2–4 mmHg systolic rise).[10]

– Total testosterone to confirm mid-normal target.

– Haematocrit/FBC — the most important safety parameter.

– PSA in men ≥40; further urological evaluation for significant rise.

– Timepoints: review at 3 and 6 months, then annually (testosterone, HCT, PSA, symptoms).[1]

– Adverse effects:

– Common: erythrocytosis (~17% vs 3% placebo; formulation-dependent); acne/oily skin; gynaecomastia; testicular atrophy; infertility; fluid retention; gel-transfer risk.[15][14]

– Serious/less common: pulmonary embolism/VTE (increased in TRAVERSE); possible increased atrial fibrillation; increased clinical fractures (unexpected TRAVERSE signal); AKI signal.[3][4][15]

– Not shown to increase (short–medium term): MACE, prostate cancer, LUTS/acute urinary retention — though high-risk men were excluded from trials.[4][10]

– Actions for abnormal findings:

– HCT >54% (or >0.54): stop, investigate, refer haematology; consider dose reduction/formulation change/venesection before cautious restart.[17]

– PSA rise (e.g. >1.4 ng/mL/yr or confirmed >4, or new nodule): urology referral.[17][1]

– New VTE: stop and investigate.[4]

– Interactions/comorbidity: caution with anticoagulation and erythrocytosis; may worsen untreated OSA and heart failure; opioids/glucocorticoids cause reversible secondary hypogonadism (treat cause).[10][1]

– Special populations: contraindicated where fertility desired; not applicable in pregnancy/breastfeeding (male therapy; gel transfer harmful to women/children); use caution in frailty (fracture signal) and extremes of age (limited evidence, exclusions from trials).[14][4][2]

8. Contraindications and cautions

– Absolute: active/untreated prostate cancer; history of aggressive/metastatic prostate cancer; breast cancer; unevaluated prostate nodule; desire for near-term fertility; uncontrolled/high baseline haematocrit.[10][1]

– Relative / specialist input needed: severe LUTS (IPSS >19); MI or stroke within 6 months; untreated/uncontrolled heart failure; untreated severe OSA; thrombophilia or prior VTE (consider prophylactic anticoagulation before initiation); PSA >4 ng/mL, or >3 ng/mL in men at increased prostate-cancer risk, pending urology.[4][10][1]

– Harm likely > benefit: using TRT for fracture/falls prevention, cognition, or mortality/longevity in eugonadal or minimally-low men — recommend against outside research.[14][2]

9. Practical management scenarios

Scenario A — Middle-aged man with multiple cardiometabolic risk factors and low-normal/borderline testosterone. Recommendation: consider — but metabolic optimisation first (Conditional).

– Assessment: confirm two fasting morning testosterone values + free T/SHBG; screen OSA, HbA1c, lipids, HCT, PSA. Most such men have functional hypogonadism.

– Shared decision-making: explain that weight loss/exercise (± GLP-1/GIP agonists) can raise testosterone ~10–30% and improve symptoms; TRT gives no proven CV benefit.[15][9][6]

– Initiation: trial lifestyle ± metabolic pharmacotherapy for 6–12 months; add TRT only if symptoms persist with reproducibly low levels and no contraindication.[9]

– Monitoring/escalation: 3/6/12-month reviews; stop if no symptomatic benefit at ~6 months or HCT/PSA thresholds breached.

Scenario B — Older, frail man with multimorbidity. Recommendation: restrict/avoid unless clear symptomatic organic hypogonadism (Conditional-to-avoid).

– Assessment: confirm biochemistry; carefully weigh fracture signal, VTE and erythrocytosis risk; assess falls, cognition, prostate.[4][2]

– Consent: be explicit that mobility/disability/mortality benefit is unproven and fractures were increased in TRAVERSE.[4]

– Initiation: prefer transdermal gel (titratable, lower erythrocytosis); low target (mid-normal).

– Monitoring/stop: close HCT surveillance; stop for lack of benefit, rising HCT/PSA, or new VTE/AF.

Scenario C — Man already under specialist care (e.g. established organic hypogonadism or on other therapy). Recommendation: offer/continue as adjunct with coordination (Strong for confirmed organic hypogonadism).

– Assessment: confirm diagnosis and existing specialist plan; reconcile monitoring to avoid duplication.

– Shared care: liaise with NHS endocrinology/urology; align PSA/HCT monitoring and targets.[1]

– Initiation/continuation: maintain licensed formulation at mid-normal target; avoid supraphysiological “optimisation.”

– Escalation: refer back to specialist for PSA rise, refractory erythrocytosis, VTE, or new prostate findings.

10. Research gaps and future directions

– Long-term (>3–5 year) safety — prostate cancer, CV events, VTE, atrial fibrillation, and the unexpected fracture signal all need dedicated long-duration study.[7][8][4]

– Longevity/hard outcomes: no adequately powered trial addresses all-cause mortality, disability-free survival, or healthspan; these remain research-only goals.[14]

– Functional hypogonadism: optimal sequencing of lifestyle, GLP-1/GIP agonists and TRT, and whether TRT adds value over metabolic therapy alone.[15][6]

– Translating surrogate gains to function: combining testosterone (or SARMs) with structured resistance/aerobic exercise to convert lean-mass gains into meaningful functional/fall/fracture outcomes.[2][6]

– Where practice should be confined to trials/registries: any use aimed at anti-ageing, longevity, or supraphysiological “optimisation” in eugonadal men, and all SARM use.[2]

References

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2. Androgens and Selective Androgen Receptor Modulators to Treat Functional Limitations Associated With Aging and Chronic Disease. Bhasin S, Krishnan V, Storer TW, Steiner M, Dobs AS. The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. 2023;78(Suppl 1):25-31. doi:10.1093/gerona/glad027.
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5. Discordance Between Online Information and Male Hypogonadism Clinical Guidelines: A Global Multilingual Content Analysis. Grant B, de Silva NL, Gumssani M, et al. The Journal of Clinical Endocrinology and Metabolism. 2026;111(6):1651-1663. doi:10.1210/clinem/dgaf689.
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13. Cardiovascular and Prostate Cancer Risk Associated to Testosterone Replacement Therapy – A Systematic Review and Meta-Analysis of 41 Randomized Controlled Trials. García-Becerra CA, Arias-Gallardo MI, Juárez-García JE, et al. International Journal of Impotence Research. 2026;:10.1038/s41443-026-01237-4. doi:10.1038/s41443-026-01237-4.
14. Efficacy and Safety of Testosterone Treatment in Men: An Evidence Report for a Clinical Practice Guideline by the American College of Physicians. Diem SJ, Greer NL, MacDonald R, et al. Annals of Internal Medicine. 2020;172(2):105-118. doi:10.7326/M19-0830.
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18. Nonpharmacological Interventions for the Management of Testosterone and Sperm Parameters: A Scoping Review. Santos HO, Cadegiani FA, Forbes SC. Clinical Therapeutics. 2022;44(8):1129-1149. doi:10.1016/j.clinthera.2022.06.006.
19. Testosterone Replacement in Men With Sexual Dysfunction. Lee H, Hwang EC, Oh CK, et al. The Cochrane Database of Systematic Reviews. 2024;1:CD013071. doi:10.1002/14651858.CD013071.pub2.