Testosterone
The endogenous male sex hormone and reference molecule of all AAS. FDA-approved TRT (testosterone replacement therapy) for hypogonadism.
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WHAT IS TESTOSTERONE?
Detailed overview
Testosterone is the primary androgenic steroid of the human body, produced by Leydig cells in the testes under LH stimulation. Anabolic:androgenic ratio 100:100, the reference point for all synthetic AAS. FDA-approved clinical indication: primary and secondary hypogonadism (Testosterone Cypionate, Enanthate, Undecanoate, transdermal gels). In sports context WADA-banned, but legitimate long-term use within medical TRT is increasingly documented. The TRAVERSE trial (Lincoff 2023, NEJM) confirmed the cardiovascular safety of transdermal TRT in hypogonadal men with elevated CV risk, a landmark revision of the earlier 2014 FDA warning narrative.
Mechanism
AR agonist, aromatizes to E2
Anabolic:Androgenic
100:100
Half-life
8 d (Cyp), 10.5 d (Ena)
Onset
24-72 h (injected ester)
Legal status
FDA Rx TRT, WADA banned
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 8
- Erythrocytosis / polycythemia: rise in hematocrit and hemoglobin (often >54% hematocrit), increasing blood viscosity and the risk of thrombosis, stroke and myocardial infarction; the most common dose-limiting effect, requiring monitoring and phlebotomy if needed.
- HPTA suppression and reduced fertility: exogenous testosterone suppresses LH/FSH, causing testicular atrophy, lower intratesticular testosterone and reduced sperm count (often to azoospermia); recovery of fertility can take months and is rarely persistent.
- Estrogenic effects from aromatization: CYP19 aromatase converts it to estradiol, which at higher doses can cause water retention, raised blood pressure, mood swings and gynecomastia (breast tissue growth).
- Adverse lipid changes and cardiovascular strain: HDL (good cholesterol) drops, LDL may rise, and supraphysiologic doses raise blood pressure and left-ventricular load, increasing long-term atherosclerosis risk.
- Androgenic skin and hair effects: can cause acne, oily skin and increased body hair; conversion to DHT (5-alpha-reductase) can accelerate male-pattern baldness in genetically predisposed individuals.
- Prostate effects: can worsen benign prostatic hyperplasia (BPH) and urinary symptoms, with a mild PSA rise; may stimulate pre-existing prostate cancer, so PSA and prostate monitoring are warranted over age 40.
- Form-specific reactions: injectable esters can cause injection-site pain (PIP), inflammation or rarely sterile abscess (propionate and aqueous suspension are especially painful); transdermal gel causes skin irritation and can transfer to others (women, children) via skin contact.
- Psychological and behavioral effects: supraphysiologic doses can cause irritability, aggression, mood lability and sleep disturbance; prolonged high-dose use can lead to AAS dependence (Kanayama 2009).
Contraindications · 7
- Known or suspected prostate carcinoma or male breast cancer: testosterone can stimulate androgen-sensitive tumor growth and is absolutely contraindicated.
- Pregnancy and breastfeeding: testosterone is teratogenic, can virilize a female fetus and passes into breast milk; extra caution is required in women of childbearing potential.
- Untreated or severe erythrocytosis / polycythemia (hematocrit roughly >54%): the raised blood viscosity creates thrombosis, stroke and heart-attack risk, and therapy must be held until hematocrit normalizes.
- Severe, decompensated heart failure (NYHA III–IV): fluid retention and volume load can precipitate decompensation.
- Active plans to father a child / fertility goal: testosterone suppresses spermatogenesis, so it should be avoided when conception is planned; a fertility-sparing protocol (e.g. hCG, clomiphene) is preferred instead.
- Untreated severe obstructive sleep apnea: testosterone can worsen apnea, so the sleep apnea should be treated first.
- Untreated hypertension, severe coronary artery disease or a recent thrombotic event (MI/stroke): cardiovascular strain and increased blood viscosity raise the risk.
Related Performance Compounds
Same therapeutic category
Studies
Related research and clinical findings
The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men
Bhasin S, Storer TW, Berman N et al.
Testosterone dose-response relationships in healthy young men
Bhasin S, Woodhouse L, Casaburi R et al.
Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline
Bhasin S, Brito JP, Cunningham GR et al.
Anabolic-androgenic steroid dependence: an emerging disorder
Kanayama G, Brower KJ, Wood RI, Hudson JI, Pope HG Jr.
Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement
Pope HG Jr, Wood RI, Rogol A, Nyberg F, Bowers L, Bhasin S.
Effects of testosterone treatment in older men (Testosterone Trials)
Snyder PJ, Bhasin S, Cunningham GR et al.
Cardiovascular safety of testosterone-replacement therapy (TRAVERSE)
Lincoff AM, Bhasin S, Flevaris P et al.
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The information here is for educational and scientific purposes only. Performance-enhancing compounds (AAS, prohormones, stimulants, doping agents) are illegal without prescription in Hungary and most of the EU, and carry serious health and legal risks. WADA bans them in competitive sport. This is NOT a usage guide, and we do not encourage any illegal use. If you do use them, medical supervision and regular bloodwork are ESSENTIAL. Severe endocrine, cardiovascular, hepatic and psychiatric side effects are possible.