Testosterone
Also known as: Test, Test C, Test E, Test P, Testosterone Cypionate, Testosterone Enanthate, Testosterone Propionate, Depo-Testosterone, Delatestryl, TRT, Testosterone Replacement Therapy
Anabolic-Androgenic Steroid | Primary Male Sex Hormone
Overview
Testosterone is the primary endogenous androgenic-anabolic steroid hormone produced mainly by the Leydig cells of the testes in males and in smaller quantities by the ovaries and adrenal glands in females. It is essential for the development and maintenance of male reproductive tissues, secondary sexual characteristics, muscle mass, bone density, red blood cell production, and overall well-being. Exogenous testosterone has been FDA-approved for the treatment of male hypogonadism since the 1950s and remains the gold standard for testosterone replacement therapy (TRT). It is available in multiple pharmaceutical formulations including intramuscular injectables, transdermal gels, transdermal patches, subcutaneous pellets, and oral capsules. In supraphysiological doses, testosterone is also widely used for performance enhancement, though such use falls outside approved medical indications.
Key benefits
- Restoration of normal testosterone levels in hypogonadal men
- Increased lean muscle mass and strength
- Improved bone mineral density and reduced fracture risk
- Enhanced libido, sexual function, and erectile quality
- Improved mood, energy, motivation, and cognitive clarity
- Reduction in body fat percentage, particularly visceral fat
- Increased red blood cell production and oxygen-carrying capacity
- Improved insulin sensitivity and metabolic health markers
Mechanism of action
Testosterone exerts its effects primarily through binding to the intracellular androgen receptor (AR), forming a hormone-receptor complex that translocates to the nucleus and modulates gene transcription. This drives protein synthesis in skeletal muscle (anabolic effect), stimulates erythropoietin production in the kidneys to increase red blood cell mass, promotes osteoblast activity and bone mineral density, and regulates libido and cognitive function. Testosterone is also converted to dihydrotestosterone (DHT) by the enzyme 5-alpha reductase in peripheral tissues (skin, prostate, hair follicles), where DHT mediates androgenic effects with greater potency. Additionally, testosterone is aromatized to estradiol by the enzyme aromatase in adipose tissue, which is important for bone health, lipid metabolism, and cardiovascular function but can cause estrogenic side effects at supraphysiological doses.
Molecular data
- Type
- Steroid hormone (C19H28O2)
- Half-life
- ~8 days (cypionate)
Indications
What the research community uses this compound for, with self-reported effectiveness.
Endocrine / Hormonal
Body Composition
Sexual Health
Metabolic Health
Neurological / Mood
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 100-200 mg/week | 1-2x per week | — |
| — | 80-100 mg/week | 2x per week (40-50 mg per injection) | — |
| — | 25-50 mg every other day | Every other day or 3x per week | — |
| — | 300-500 mg/week | 2x per week | — |
| — | 500-750 mg/week | 2-3x per week | — |
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 50-100 mg daily (1-2 pumps) | Once daily, morning application | — |
| — | 50-200 mg daily | Once or twice daily | — |
| — | 2-6 mg daily | Once daily, applied at night | — |
Protocol variations
Alternative cycling patterns reported in the literature and community.
Testosterone Cypionate
Cypionate is the most widely prescribed testosterone ester in the United States. Its 8-day half-life provides relatively stable serum levels with once or twice weekly injections. Available as Depo-Testosterone (brand) and generic formulations in cottonseed or sesame oil carriers.
Testosterone Enanthate
Enanthate is the most widely used testosterone ester worldwide and the standard in most countries outside the US. Its pharmacokinetic profile is nearly identical to cypionate with a 7-8 day half-life. Available as Delatestryl (brand) and numerous international generics.
Testosterone Propionate
Propionate is the shortest commonly used testosterone ester with a 2-3 day half-life. It requires more frequent injections (every other day or every day) but allows for faster dose adjustments and clears the system quickly. Often preferred at the end of a cycle before PCT, or by those who want rapid dose titration.
Testosterone Undecanoate
Undecanoate is available in two formulations: an ultra-long-acting injectable (Nebido/Aveed) with a half-life of ~21 days given every 10-14 weeks, and an oral capsule (Jatenzo) taken twice daily with food. The injectable version offers maximum convenience with only 4-6 injections per year but requires clinic administration and offers limited dose flexibility.
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Acne and oily skin (increased sebum production via DHT)
- Water retention and bloating (estrogen-mediated)
- Mild mood changes (irritability, increased assertiveness)
- Increased hematocrit and hemoglobin (erythrocytosis)
- Testicular atrophy (suppression of LH/FSH from exogenous testosterone)
- Injection site pain, redness, or irritation
- Increased body hair growth
- Mild elevation in blood pressure
Rare side effects
- Gynecomastia (breast tissue growth from excess estradiol conversion)
- Polycythemia vera requiring phlebotomy (hematocrit above 54%)
- Sleep apnea onset or worsening
- Significant HDL cholesterol suppression
- Hepatotoxicity (primarily oral methylated formulations, not injectable esters)
- Left ventricular hypertrophy with long-term supraphysiological doses
- Azoospermia (complete suppression of sperm production)
Contraindications
- Prostate cancer (active or history of hormone-sensitive prostate cancer)
- Breast cancer in males
- Polycythemia (hematocrit above 54% at baseline)
- Uncontrolled severe heart failure
- Untreated severe obstructive sleep apnea
- Desire for near-term fertility (without concurrent HCG/FSH)
- Pregnancy or potential exposure to pregnant women (Category X)
- Hypersensitivity to testosterone or any formulation components
Monitoring
- Total and free testosterone: 6-8 weeks after starting, then every 6-12 months
- Estradiol (sensitive assay): at each testosterone lab draw
- Complete blood count with hematocrit: baseline, 3-6 months, then annually
- Comprehensive metabolic panel and lipid panel: baseline, 6 months, then annually
- PSA (prostate-specific antigen): baseline, 3-6 months, then annually for men over 40
- Digital rectal exam: annually for men over 40
- DEXA scan for bone density: if indicated by risk factors, at baseline and 1-2 years
References
Primary literature and clinical-trial data informing this entry.