Testosterone cypionate (Depo-Testosterone) has an elimination half-life of approximately 8 days following deep intramuscular injection[1], per the FDA prescribing information for Depo-Testosterone (NDA 009166). The 17β-cypionate ester is hydrolyzed in vivo to release free testosterone; esterification and intramuscular depot formation extend the effective half-life from approximately 10–100 minutes (free testosterone IV) to approximately 8 days[1]. This pharmacokinetic profile supports once-weekly or every-2-week intramuscular injection for testosterone replacement therapy. Testosterone cypionate metabolites are detectable in urine for up to 3 months by WADA-certified methods[2].
| Parameter | Value | Source |
|---|---|---|
| Elimination Half-Life (IM) | ~8 days | FDA NDA 009166 [1] |
| Half-Life — Free Testosterone (IV) | ~10–100 minutes | FDA NDA 009166 [1] |
| Time to Peak (Tmax) — IM | ~2–4 days | FDA NDA 009166 [1] |
| Route(s) of Administration | Intramuscular injection (approved); Subcutaneous (off-label) | — |
| Full Clearance (5 half-lives) | ~40 days | Calculated |
| Urine Detection Window | Up to ~3 months (WADA LC-MS/MS) | WADA [2] |
| Ester Weight — Testosterone Content | ~70% testosterone by weight | Calculated from MW |
| Standard TRT Dose | 100–200 mg IM every 1–2 weeks | FDA NDA 009166 [1] |
| Data Quality | Human PK Study — half-life from FDA-approved human pharmacokinetic data | |
Testosterone cypionate has an elimination half-life of approximately 8 days after intramuscular injection, per FDA prescribing information for Depo-Testosterone (NDA 009166)[1]. The elimination half-life is the time required for plasma concentration of a drug to fall by 50% from its peak. For testosterone cypionate, this reflects the combined kinetics of ester hydrolysis from the intramuscular depot and hepatic clearance of the resulting free testosterone.
The ~8-day half-life of testosterone cypionate is derived from human pharmacokinetic studies using serum testosterone measurements following a single intramuscular injection. After peak serum concentrations are reached at approximately 2–4 days post-injection (Tmax), concentrations decline log-linearly, consistent with first-order elimination kinetics. The slope of this decline gives the elimination rate constant (k), and the half-life is calculated as t½ = 0.693 / k.
Unlike intravenous free testosterone (which is eliminated with a half-life of only ~10–100 minutes), the cypionate ester creates a subcutaneous or intramuscular oil depot. The rate-limiting step for elimination is ester hydrolysis from the depot, not hepatic clearance — which is why the effective half-life is dramatically extended.
The elimination half-life describes the rate at which testosterone leaves the bloodstream — it does not directly describe how long therapeutic effects are maintained. Biological effects of testosterone (androgen receptor activation, nitrogen retention, libido, erythropoiesis stimulation, hematocrit changes) require sustained above-threshold androgen receptor occupancy.
At steady state with weekly dosing, serum testosterone concentrations fluctuate between a peak (approximately days 1–2 post-injection) and a trough (approximately days 6–7 before the next injection), but typically remain within the physiological-to-therapeutic range throughout the dosing interval. The half-life determines the dosing interval required to prevent concentrations from falling below the therapeutic threshold.
Using the ~8-day elimination half-life, plasma testosterone from a single injection of testosterone cypionate decreases by approximately 50% every 8 days. Clinical clearance — conventionally defined as 5 half-lives — occurs at approximately 40 days. However, urine metabolite detection by WADA-certified methods extends significantly beyond plasma clearance.
| Half-Life # | Days After Injection | Remaining in Plasma (approx.) |
|---|---|---|
| 1 | ~8 days | 50% |
| 2 | ~16 days | 25% |
| 3 | ~24 days | 12.5% |
| 4 | ~32 days | 6.25% |
| 5 (clinical clearance) | ~40 days | ~3% |
Following a single intramuscular injection of testosterone cypionate, serum testosterone rises to peak concentration at approximately 2–4 days (Tmax) and then declines with an ~8-day half-life. After approximately 40 days (5 half-lives), less than 3% of the injected dose remains in circulation. However, this does not mean testosterone metabolites are undetectable in urine — urinary markers can persist for up to 3 months post-injection using sensitive WADA analytical methods.
With weekly intramuscular injections, steady-state plasma testosterone concentrations are reached after approximately 4–5 half-lives (approximately 4–5 weeks). At steady state, the concentration fluctuates between a peak shortly after each injection and a trough just before the next dose. Weekly dosing produces smaller peak-to-trough variation than every-2-week dosing, contributing to more stable mood, libido, and energy for many patients. After stopping testosterone cypionate at steady state, plasma concentrations follow the same ~8-day half-life decline, with endogenous testosterone production typically resuming within 3–6 months depending on HPG axis suppression duration.
The ~8-day elimination half-life of testosterone cypionate has direct implications for TRT dosing protocols. Dosing frequency, dose size, and the route of administration all interact with pharmacokinetics to determine steady-state testosterone concentrations and peak-to-trough variation.
Traditional FDA-labeled TRT dosing for Depo-Testosterone is 100–200 mg IM every 1–2 weeks[1]. However, every-2-week dosing produces substantial peak-to-trough fluctuation: serum testosterone may reach supraphysiological levels (above 1000 ng/dL) at peak and fall to below-physiological levels (below 300 ng/dL) at trough. These swings are associated with mood changes, energy fluctuation, and erythrocytosis risk at supraphysiological peaks.
Weekly dosing at half the every-2-week dose (e.g., 100 mg every 2 weeks → 50 mg every week) maintains the same average weekly testosterone delivery while dramatically reducing peak-to-trough fluctuation. Many endocrinologists and urologists now prefer weekly dosing or even more frequent subcutaneous microdosing (20–40 mg 2–3 times per week) for physiologically stable testosterone levels.
This is one of the most clinically important — and most commonly misunderstood — aspects of testosterone cypionate dosing. A prescription for "200 mg testosterone cypionate" does not deliver 200 mg of bioavailable testosterone. The cypionate ester accounts for approximately 30% of the molecular weight, meaning only ~70% is actual testosterone.
The calculation is straightforward:
By comparison, testosterone enanthate (MW 400.6 g/mol) delivers approximately 72% testosterone by weight — approximately 144 mg from a 200 mg dose. When comparing TRT dosing across different ester formulations, this ester weight adjustment is essential for accurate dose equivalence. A patient switching from 200 mg testosterone enanthate to testosterone cypionate is receiving slightly less bioavailable testosterone per dose, though the clinical difference is minor at these doses.
| Compound | Half-Life | Dosing Frequency | FDA Status |
|---|---|---|---|
| Testosterone Cypionate (Depo-Testosterone) | ~8 days | Every 1–2 weeks | FDA-approved NDA 009166 |
| Testosterone Enanthate | ~4–5 days | Every 1–2 weeks | FDA-approved |
| Testosterone Propionate | ~2 days | Every 2–3 days | FDA-approved (various) |
| Testosterone Undecanoate (Aveed, IM) | ~21 days | Every 10 weeks | FDA-approved NDA 022149 |
| Route | Half-Life | Bioavailability | Tmax | Notes |
|---|---|---|---|---|
| Intramuscular (deep gluteal) | ~8 days | ~100% (ester absorbed, hydrolyzed) | ~2–4 days | FDA-approved standard route [1] |
| Subcutaneous | Not formally published (estimated longer depot release) | ~100% (estimated) | No published data | Off-label TRT use; slower absorption kinetics reported in clinical practice |
| Oral (free testosterone) | ~10 minutes (first-pass) | <1% | — | Not used; oral testosterone requires special formulations (e.g., undecanoate) |
| Intravenous (free testosterone) | ~10–100 minutes | 100% | Minutes | Reference PK route used in pharmacokinetic research; not used clinically |
Standard workplace urine drug screening panels (e.g., SAMHSA-5 or DOT 5-panel) do not test for testosterone or anabolic steroids. An employer-ordered urine drug test will not detect testosterone cypionate. Testosterone is also not included in standard pre-employment or law enforcement drug panels. Detection requires specifically ordered steroid panels, which are uncommon outside sports anti-doping contexts.
Athletes subject to WADA anti-doping regulations face a substantially longer detection window. Testosterone cypionate metabolites — particularly testosterone glucuronide and the testosterone-to-epitestosterone (T/E) ratio — can be detected in urine for up to approximately 3 months after the last injection using LC-MS/MS methods at WADA-certified laboratories[2].
WADA uses the Steroidal Module of the Athlete Biological Passport (ABP) for longitudinal monitoring of steroid hormone levels, which can detect exogenous testosterone use through population-based statistical modeling even when individual T/E ratios remain below traditional thresholds. Additionally, isotope ratio mass spectrometry (IRMS/GC-C-IRMS) can distinguish synthetic (pharmaceutical) testosterone from endogenous testosterone based on carbon-13 isotopic signatures, providing confirmatory evidence of exogenous use.
Athletes subject to WADA testing should treat testosterone cypionate as detectable for a minimum of 3 months, and potentially longer when ABP passport longitudinal data is considered.
The extended half-life of testosterone cypionate is entirely a consequence of the 17β-cypionate ester (cyclopentylpropanoate) attached to the testosterone molecule at the C-17 hydroxyl position. This esterification renders testosterone highly lipophilic — when injected in an oil vehicle (typically cottonseed or sesame oil) into deep intramuscular tissue, it forms a depot that resists rapid diffusion into the systemic circulation[1]. The rate-limiting step for testosterone availability is the gradual hydrolysis of the ester bond by tissue and plasma esterases, releasing free testosterone over approximately 8 days.
Once released as free testosterone into systemic circulation, it binds to plasma proteins: approximately 37% binds to sex hormone-binding globulin (SHBG) with high affinity, approximately 60% binds loosely to albumin, and approximately 2–3% remains unbound (free testosterone). Only free and albumin-bound testosterone are considered bioavailable for androgen receptor activation. Total testosterone assays measure all three fractions; free testosterone assays isolate the biologically active unbound fraction.
Hepatic metabolism proceeds primarily through CYP3A4 and CYP2C19 oxidation to 6β-hydroxytestosterone and other hydroxylated metabolites, followed by glucuronide conjugation (via UGT2B17 and UGT2B15) to androsterone glucuronide and androstanediol glucuronide[1]. These water-soluble conjugates are excreted renally. It is the persistence of these urinary glucuronide metabolites — not plasma testosterone — that accounts for the 3-month urine detection window in WADA testing.
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