TRT
Testosterone Replacement Therapy | Testosterone Cypionate & Enanthate
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What is TRT?
TRT refers to testosterone cypionate and enanthate — FDA-approved injectable esters of testosterone, prescribed under medical supervision for diagnosed hypogonadism (clinically low testosterone). This encyclopedia entry summarizes the regulatory history and published research on these esters as a reference point for researchers comparing hormone pharmacology, not as guidance for personal use. Nothing here is medical advice, and starting, stopping, or dosing any hormone therapy requires a licensed physician's supervision.
Key terms:
TRT is a androstane steroid with ester modification.
Testosterone Replacement Therapy (TRT) is FDA-approved for male hypogonadism, meaning low testosterone caused by testicular failure or by hypothalamic-pituitary dysfunction. Testosterone cypionate and enanthate are the most commonly prescribed injectable esters. Both hold testosterone levels steady, with injections scheduled weekly or every other week. The TRAVERSE trial, with more than 5,200 participants, reported cardiovascular safety in high-risk men when the therapy was used as indicated.
Key research areas
- Most effective TRT delivery method with predictable testosterone levels
- Intramuscular or subcutaneous administration provides sustained release over 7-8 days
- Significantly improves energy, libido, mood, muscle mass, and bone density in hypogonadal men
Researched dosing
This table reflects dosing regimens described in the clinical and prescribing literature for context and comparison — not a personal dosing recommendation; any TRT protocol requires a licensed physician.
| Phase | Dose | Frequency | Route |
|---|---|---|---|
| Standard TRT protocol | 100-200mg | Weekly or split 2x/week | IM or SubQ |
| Starting dose | 75-100mg | Weekly | IM or SubQ |
| Split-dosing studies | 50-100mg | Every 3.5 days | SubQ preferred |
| With hCG (fertility studies) | 100-150mg + 250-500 IU hCG | T weekly, hCG 2-3x/week | IM/SubQ + SubQ |
How it works
This section explains how testosterone esters work at the receptor level — this is background pharmacology for research and educational reference, not guidance on using testosterone therapy.
Testosterone esters (cypionate/enanthate) are dissolved in oil and injected, where they slowly release testosterone as the ester bond is cleaved. Cypionate has ~8-day half-life, enanthate ~7 days. Testosterone then binds to androgen receptors, modulating gene expression for anabolic and androgenic effects.
Molecular data
These figures describe the chemical structure of the testosterone esters used in TRT — reference chemistry information, not a personal-use guide.
- Weight
- 412.61 Da
- Length
- 0 amino acids
- Type
- Androstane steroid with ester modification
C27H40O3 (Cypionate) / C26H40O3 (Enanthate)
Pharmacokinetics
This chart, drawn from the FDA drug label, shows how injectable testosterone esters are absorbed and cleared over time — included here as pharmacology reference data, not instructions for use.
- Peak
- 48 hr
- Half-life
- 156 hrs
- Cleared
- ~780 hrs
FDA Depo-Testosterone label
Research applications
This section summarizes the FDA-approved indication (diagnosed hypogonadism) and the research literature behind it — a regulatory and research reference, not medical guidance for whether or how to start therapy.
Hormone Restoration
Restores serum testosterone to physiological range (400-700 ng/dL) in hypogonadal men with documented deficiency. Improves low testosterone symptoms: fatigue, low libido, erectile dysfunction, depressed mood, and cognitive fog. Exogenous testosterone suppresses sperm production; hCG co-administration may preserve fertility during TRT.
Body Composition
Intramuscular TRT associated with 5.7% increase in fat-free mass and 10-13% improvement in muscle strength. Transdermal showed 1.7% fat-free mass increase.
Metabolic Health
Moderate improvements in metabolic parameters, insulin sensitivity, and bone density with ongoing TRT.
Dosage reference
- Doses used in research
- 100–200 mg weekly, often split into two doses
- Frequency in studies
- Weekly or every 3.5 days for stable levels
- Handling
- Reconstituted solution — research use only; not for administration
- Timeline reported in studies
- Energy/mood: 3-6 weeks. Libido: 3-6 weeks. Body composition: 3-6 months
- Storage
- Room temperature 20-25°C (68-77°F). Do not refrigerate or freeze.
- Cycle length
- Ongoing lifetime therapy for diagnosed hypogonadism
- Break between cycles
- Not applicable - continuous therapy (stopping causes symptoms to return)
Interactions
This list summarizes compounds studied alongside testosterone therapy in the literature, included here as pharmacology reference, not a personal-stacking guide.
Reconstitution & storage
Testosterone esters ship as a ready-to-use oil solution rather than a powder requiring reconstitution; this section is handling and storage reference only.
- No reconstitution needed - testosterone comes as ready-to-use oil solution
- Warm vial briefly in hands if oil is thick (do not heat excessively)
- Clean vial stopper with alcohol swab
- Draw air equal to dose volume, inject into vial to ease drawing
- Invert vial and draw prescribed dose slowly (oil is viscous)
- Store the reconstituted solution refrigerated (2–8°C), labeled with the date and concentration, for laboratory research use only.
Lyophilized: 20-25°C (68-77°F), use within Per manufacturer expiration date
Reconstituted: 2-6°C, use within N/A - supplied as ready-to-use oil solution
Quality indicators
These are the sourcing and verification notes researchers and patients use to distinguish pharmaceutical-grade testosterone from unregulated sources — reference information, not a purchasing recommendation.
Pharmaceutical Grade Product - Use only FDA-approved testosterone from licensed pharmacies. Brand names: Depo-Testosterone (cypionate), Delatestryl (enanthate).
Clear Oil Solution - Testosterone should be clear, yellowish oil. No particles, cloudiness, or crystallization visible.
Proper Storage Verification - Stored at controlled room temperature. If crystallized from cold exposure, warm gently until dissolved.
Compounded Testosterone - Compounded products may vary in quality. Use only from licensed compounding pharmacies with COA available.
Underground Lab (UGL) Products - UGL testosterone has inconsistent dosing (25-400% of labeled amount), contamination risks, and no quality control.
Crystallized or Cloudy Solution - Crystallization from cold exposure requires gentle warming. Persistent cloudiness or particles indicates contamination.
What to expect
This timeline summarizes what the clinical literature reports for patients under physician-supervised TRT — research and regulatory context, not a personal-results promise or treatment plan.
Initial adjustment, possible mood fluctuations as levels stabilize
Improved energy, mood, mental clarity, and libido typically begin
Enhanced recovery from exercise, improved sleep quality
Body composition changes become noticeable (muscle development, fat reduction)
Bone density improvements, sustained metabolic benefits
Safety notes
This section summarizes TRT's FDA safety data and regulatory notes, including its black-box warning — regulatory and research reference only; monitoring and treatment decisions belong to a licensed physician.
- Requires diagnosis of hypogonadism with documented low testosterone (<300 ng/dL) plus symptoms
- Regular monitoring required: testosterone, hematocrit, PSA, estradiol every 3-6 months initially
- Hematocrit >54% requires intervention (dose reduction, therapeutic phlebotomy)
- Not for use by women (especially pregnant), children, or men with prostate/breast cancer
- May cause testicular atrophy and infertility - discuss hCG if fertility desired
- FDA-approved for male hypogonadism treatment
- FDA black box warning: possible increased risk of heart attack and stroke
Regulatory status
- Approved by the FDA for at least one indication. That approval applies to regulated pharmaceutical products, not to research-grade material.
- Supplied and described for laboratory research use only — not for human or veterinary use.
Community data
Community Insights
Based on data the community reported. Not clinical proof.
References
TRT noninferior to placebo for major adverse cardiac events in 5,246 hypogonadal men with cardiovascular disease or high CV risk (TRAVERSE trial)
Testosterone gel increased lean mass, improved sexual function, mood, and walking distance in 788 older hypogonadal men (TTrials)
Meta-analysis of 31 RCTs: IM TRT associated with 5.7% increase in fat-free mass and 10-13% improvement in muscle strength