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Neuropsychiatric

Testosterone Cypionate

Test C

Testosterone cypionate ("Test C") is a long-acting, oil-based ester of testosterone given by intramuscular (or subcutaneous) injection. It is the same molecule the body makes, formulated as a slow-release depot; clinically it is used as testosterone-replacement therapy (TRT) for men with diagnosed hypogonadism (low testosterone from disease of the testes, pituitary, or hypothalamus). It is also widely used non-medically at supraphysiologic doses to build muscle and strength. The main risks are that it reliably raises red-blood-cell mass (erythrocytosis/polycythemia), which thickens the blood and can raise clot/stroke risk; it shuts down the body's own testosterone and sperm production (HPTA suppression, testicular shrinkage, often reversible infertility); at high or prolonged doses it is linked to heart-muscle dysfunction and accelerated coronary plaque, adverse cholesterol shifts, mood/aggression changes and dependence. Unlike oral 17-alpha-alkylated steroids, injectable testosterone esters are not markedly liver-toxic. Even at replacement doses a large randomized trial found more atrial fibrillation, pulmonary embolism and acute kidney injury. This is educational information only, not medical advice, and does not create a doctor-patient relationship; these substances carry serious risks and require a qualified physician and regular bloodwork. 21+ only.

Clinical readoutAAS · injectable-testosterone
Hepatic strainLow
CardiovascularHigh
HPTA suppressionVery high
Half-life
8 d
Route
Deep intramuscular inje…
Evidence
A
Active
After a single intramus…
8 d16 d3.4 wk4.6 wk5.7 wk
Illustrative single-compartment washout · each mark = one half-life · t½ ≈ Long-acting depot ester. Reported terminal elimination half-life of released testosterone is on the order of roughly 8 days for cypionate, modestly longer than testosterone enanthate (~4.5 days); wide inter-individual variation. Absorption from the oil depot, not elimination, is rate-limiting.
Pharmacology

Mechanism of action

Testosterone cypionate is a prodrug depot: after injection the cypionate ester is slowly released from the oil and hydrolyzed to free testosterone. Testosterone binds the androgen receptor to drive protein synthesis, muscle hypertrophy and secondary sexual characteristics; it is also converted by 5-alpha-reductase to the more potent androgen dihydrotestosterone (DHT) and by aromatase to estradiol, which mediate several effects (prostate/skin/hair effects via DHT; bone, mood and gynecomastia via estradiol). Exogenous testosterone suppresses hypothalamic GnRH and pituitary LH/FSH by negative feedback, shutting down endogenous testicular testosterone and sperm production. It stimulates erythropoiesis by raising erythropoietin and suppressing hepcidin, increasing red-cell mass.
Kinetics

Pharmacokinetics

Half-life

Long-acting depot ester. Reported terminal elimination half-life of released testosterone is on the order of roughly 8 days for cypionate, modestly longer than testosterone enanthate (~4.5 days); wide inter-individual variation. Absorption from the oil depot, not elimination, is rate-limiting.

Active duration

After a single intramuscular injection, serum testosterone peaks within ~24-72 hours and then declines over roughly 1-2 weeks, which is why replacement dosing intervals are typically about 1-2 weeks; supraphysiologic non-medical use produces sustained elevations.

Route

Deep intramuscular injection of an oil solution (subcutaneous injection is also used clinically). Not orally active in this ester form.

Metabolism & clearance

Ester is cleaved to free testosterone, which is metabolized hepatically (and peripherally) to DHT and estradiol and inactivated by oxidation/conjugation, with renal excretion of conjugated 17-ketosteroid metabolites. For washout/monitoring reasoning (not detection avoidance), effective clearance after stopping cypionate takes several weeks (roughly 5-6 weeks, ~5 half-lives), and HPTA recovery lags further behind.

For monitoring and washout planning, not drug-test evasion.

Reported effects

Physiological & performance effects

  • Raises serum testosterone into or above the physiological range depending on dose, correcting symptoms of hypogonadism (low libido, fatigue, erectile dysfunction) in deficient men
  • Increases fat-free mass, muscle size and strength, especially at supraphysiologic doses and with resistance training
  • Modest improvements in sexual desire, erectile function and sexual activity in hypogonadal/older men
  • Small improvements in mood and depressive symptoms reported at replacement doses in older men
  • Increases hemoglobin and hematocrit (red-cell mass)
  • Suppresses endogenous LH/FSH, testicular testosterone and spermatogenesis (basis of hormonal male contraception research)
Safety

Adverse effects by system

Cardiovascular

At replacement doses in men with high cardiovascular risk, a large RCT found no increase in major adverse cardiac events (MACE) but a higher incidence of atrial fibrillation and pulmonary embolism. Long-term supraphysiologic (non-medical) use is associated in cohort data with reduced left-ventricular systolic and diastolic function and accelerated coronary atherosclerosis. Erythrocytosis, adverse HDL-cholesterol reduction and raised blood pressure add further cardiovascular strain.

Hepatic

Injectable testosterone esters are not 17-alpha-alkylated and, unlike oral alkylated anabolic steroids, are not considered markedly hepatotoxic; long-term injectable AAS users have shown liver enzymes within the normal range. Cholestasis, peliosis hepatis and hepatic tumors are chiefly a problem of oral 17-alpha-alkylated agents, not injectable testosterone.

Endocrine / HPTA

Marked, dose-dependent suppression of the hypothalamic-pituitary-testicular axis: LH and FSH fall, endogenous testosterone and spermatogenesis are suppressed, and the testes atrophy. Recovery after stopping is variable and can be prolonged, especially after high-dose or long-duration use.

Reproductive

Testicular atrophy and suppressed spermatogenesis causing oligospermia or azoospermia and reduced fertility; aromatization to estradiol can cause gynecomastia. In pooled hormonal-contraception data sperm output recovered in essentially all men (median ~3.4 months, ~90% by 12 months, ~100% by 24 months), but this was in eugonadal men on time-limited protocols and may not predict recovery after long high-dose use.

Neuropsychiatric

Evidence is mixed and dose-dependent. Replacement doses were associated with slightly better mood/lower depressive symptoms and, in one controlled study of 600 mg/week for 10 weeks, no measurable mood or behavior change. Illicit high-dose use is associated with irritability, aggression, hypomanic/psychotic symptoms, dependence, and depression (including suicidality) during withdrawal.

Renal

In the TRAVERSE RCT, acute kidney injury occurred more often in the testosterone group than placebo. Broader high-quality renal-outcome data for injectable testosterone are limited; supraphysiologic AAS use has separately been linked to kidney injury but with weaker evidence.

Hematologic

Reliably increases hemoglobin and hematocrit via increased erythropoietin and suppressed hepcidin, and can produce clinically significant erythrocytosis/polycythemia that raises blood viscosity and thromboembolic risk. This is one of the most consistent and monitorable adverse effects.

Dermatologic

Androgenic skin effects such as acne and oily skin are recognized, and DHT-mediated effects can accelerate male-pattern scalp hair loss in predisposed individuals. Direct trial-quality dermatologic data specific to cypionate are limited; topical testosterone formulations (not this injectable) commonly cause application-site skin reactions.

Recovery

HPTA suppression & recovery

Suppression: Marked / near-complete during use

Exogenous testosterone suppresses LH/FSH and endogenous testosterone and sperm production; on stopping, recovery of the HPT axis is variable and can be slow, particularly after high-dose or prolonged use. Pooled male-contraception data show sperm output recovers in nearly all eugonadal men within months to ~2 years, but this may not generalize to long high-dose non-medical use. Any recovery approach should be directed by an endocrinologist; only single-SERM strategies are within scope here and dual-SERM protocols are out of scope. Prolonged or permanent hypogonadism is possible and warrants specialist evaluation.

Bloodwork & vitals

Monitoring

Recommended labs & checks
Total (and where available free) testosteroneComplete blood count / hematocrit and hemoglobinProstate-specific antigen (PSA) in age-appropriate menFasting lipid panelEstradiolLH and FSH (to document suppression/recovery)Liver function tests (baseline and periodic)Blood pressure

Cadence: Baseline before starting; recheck testosterone, hematocrit, PSA and symptoms at roughly 3 and 6-12 months, then at least annually if stable. Check hematocrit at 3, 6 and 12 months because erythrocytosis often emerges early; reduce dose, hold, or arrange therapeutic phlebotomy for a high hematocrit under clinician guidance.

Warning signs — seek care
  • Chest pain, shortness of breath, or leg swelling/pain (possible clot, pulmonary embolism, or cardiac event) - seek emergency care
  • Severe headache, visual changes, dizziness or ruddy complexion (possible polycythemia/stroke risk)
  • Palpitations or irregular heartbeat (atrial fibrillation)
  • Marked mood change, aggression, mania, or suicidal thoughts
  • Reduced urine output or new swelling (possible kidney injury)
  • Yellowing of skin/eyes or severe abdominal pain (evaluate liver)
  • New or worsening urinary obstruction, or a rising PSA
Do not use if

Contraindications

  • Known or suspected prostate cancer or male breast cancer
  • Baseline erythrocytosis / elevated hematocrit (e.g. hematocrit above ~50-54%) until corrected
  • Men actively seeking fertility (suppresses spermatogenesis)
  • Uncontrolled or severe heart failure and recent major cardiovascular event
  • Untreated severe obstructive sleep apnea
  • Personal history of venous thromboembolism or known thrombophilia (relative contraindication)
  • Pregnancy and women of childbearing potential (virilizing/teratogenic); avoid skin transfer to women and children
  • Severe untreated lower urinary tract symptoms from benign prostatic hyperplasia (relative)
Combinations

Interaction profile

  • MajorWith another anabolic steroid: Additive cardiovascular strain
  • MajorWith a thermogenic stimulant: Additive cardiovascular strain
  • ModerateWith thyroid hormone: Additive cardiovascular strain
  • ModerateWith growth hormone: Additive cardiovascular strain
  • MajorWith another anabolic steroid: Blood / clotting
  • MajorWith a clot-promoting SERM: Blood / clotting
  • ModerateWith an aromatase inhibitor: Hormonal
  • ModerateWith an anabolic steroid: Hormonal
  • ContraindicatedWith DNP: Additive cardiovascular strain

Check a specific combination in the interaction checker.

Harm reduction

Reducing harm & when to stop

  • This is educational information only and not medical advice; testosterone should be used under a physician with regular bloodwork, not self-directed.
  • Get baseline labs before any use (testosterone, hematocrit/hemoglobin, PSA, lipids, estradiol, LH/FSH, liver panel, blood pressure) and repeat on a schedule; do not fly blind.
  • Hematocrit is the single most important routine safety check: a rising or high hematocrit (roughly >52-54%) means increased clot/stroke risk and should prompt dose reduction, holding, or clinician-directed phlebotomy.
  • Stop and seek emergency care for chest pain, breathlessness, one-sided leg swelling, severe headache/visual change, or signs of stroke - these can signal clots, embolism or a cardiac event.
  • Seek prompt care for marked mood change, aggression, or suicidal thoughts, and for jaundice or dark urine.
  • Understand that fertility and natural testosterone production are suppressed during use; recovery is variable and sometimes prolonged - discuss with an endocrinologist before starting if fertility matters.
  • Do not use if you have or may have prostate or breast cancer, uncontrolled heart failure, untreated severe sleep apnea, or a personal/strong family clotting history without specialist clearance.
  • Any recovery/HPTA plan should be directed by an endocrinologist; only single-SERM approaches are within scope and dual-SERM protocols are out of scope here.
  • Avoid skin/needle transfer and safely dispose of sharps; keep formulations away from women and children.
Evidence

Citations (16)

Every clinical claim above is tied to a primary source. Overall evidence grade A — graded to the best available evidence for its core claims.

  1. 01

    Testosterone-replacement therapy in middle-aged/older hypogonadal men with high cardiovascular risk was non-inferior to placebo for major adverse cardiac events, but showed higher incidence of atrial fibrillation, pulmonary embolism and acute kidney injury.

    RCTCardiovascular Safety of Testosterone-Replacement Therapy.PMID 37326322 ↗

  2. 02

    In hypogonadal men carefully screened, testosterone vs placebo did not significantly increase high-grade or any prostate cancer, but PSA increased more with testosterone.

    RCTProstate Safety Events During Testosterone Replacement Therapy in Men With Hypogonadism: A Randomized Clinical Trial.PMID 38150256 ↗

  3. 03

    Raising testosterone to mid-normal range in older men improved sexual function/activity and slightly improved mood and depressive symptoms.

    RCTEffects of Testosterone Treatment in Older Men.PMID 26886521 ↗

  4. 04

    Supraphysiologic testosterone (600 mg/week enanthate for 10 weeks) increased fat-free mass, muscle size and strength; no mood or behavior change was detected in this controlled setting.

    RCTThe effects of supraphysiologic doses of testosterone on muscle size and strength in normal men.PMID 8637535 ↗

  5. 05

    Testosterone increases hemoglobin and hematocrit by roughly 7-10% via increased erythropoietin and suppressed hepcidin, consistent with a new EPO/hemoglobin set point.

    RCTTestosterone induces erythrocytosis via increased erythropoietin and suppressed hepcidin: evidence for a new erythropoietin/hemoglobin set point.PMID 24158761 ↗

  6. 06

    Testosterone is a recognized cause of drug-induced (acquired) erythrocytosis.

    ReviewJAK2 unmutated erythrocytosis: 2023 Update on diagnosis and management.PMID 36966432 ↗

  7. 07

    Long-term illicit anabolic-androgenic steroid use is associated with reduced left-ventricular systolic and diastolic function and accelerated coronary atherosclerosis, with plaque burden related to cumulative dose.

    CohortCardiovascular Toxicity of Illicit Anabolic-Androgenic Steroid UsePMID 28533317 ↗

  8. 08

    AAS use is associated with dependence, aggression/violence during use, and depression/suicidality during withdrawal, and can act as a gateway to opioid use.

    CohortPast anabolic-androgenic steroid use among men admitted for substance abuse treatment: an underrecognized problem?PMID 12633124 ↗

  9. 09

    17-alpha-alkylated (oral) AAS are hepatotoxic (cholestasis, peliosis, tumors) whereas non-alkylated agents such as injectable testosterone esters are not considered markedly hepatotoxic.

    ReviewAnabolic androgenic steroid-induced hepatotoxicity.PMID 27372877 ↗

  10. 10

    AAS adverse effects include raised hematocrit and thromboembolism, arrhythmias/cardiomyopathy, 17-alpha-alkylated liver toxicity, and psychiatric effects including aggression and withdrawal depression.

    ReviewDoping with anabolic androgenic steroids (AAS): Adverse effects on non-reproductive organs and functions.PMID 26373946 ↗

  11. 11

    In long-term injectable-AAS-using bodybuilders three months after withdrawal, liver enzymes and lipid profiles were within the normal range and not significantly different from non-users.

    CohortBody composition, cardiovascular risk factors and liver function in long-term androgenic-anabolic steroids using bodybuilders three months after drug withdrawal.PMID 8884417 ↗

  12. 12

    After hormonal suppression of spermatogenesis, sperm output recovered in essentially all eugonadal men (median ~3.4 months; ~90% by 12 months; ~100% by 24 months).

    Meta-analysisRate, extent, and modifiers of spermatogenic recovery after hormonal male contraception: an integrated analysis.PMID 16650651 ↗

  13. 13

    Testosterone cypionate and enanthate injections produce sustained elevations of serum testosterone in men, supporting depot dosing intervals of about 1-2 weeks.

    CohortComparison of testosterone, dihydrotestosterone, luteinizing hormone, and follicle-stimulating hormone in serum after injection of testosterone enanthate of testosterone cypionate.PMID 7353699 ↗

  14. 14

    Intramuscular testosterone esters behave as slow-release depots with terminal half-life estimates on the order of several days (testosterone enanthate ~4.5 days).

    PreclinicalPharmacokinetics and pharmacodynamics of testosterone enanthate and dihydrotestosterone enanthate in non-human primates.PMID 2333732 ↗

  15. 15

    Exogenous testosterone replacement normalizes serum testosterone and suppresses LH in hypogonadal men.

    CohortLong-term efficacy and safety of a permeation-enhanced testosterone transdermal system in hypogonadal men.PMID 9497881 ↗

  16. 16

    No testosterone-therapy trial before TRAVERSE was adequately powered for cardiovascular events, so earlier signals of possible harm were inconclusive; testosterone affects lipids, platelets and vascular function.

    ReviewTestosterone replacement therapy and cardiovascular risk.PMID 31123340 ↗

Last reviewed 2026-07-06 · Verified against PubMed · Educational, not medical advice