Testosterone Cypionate
Test Cyp · TC
Standard US TRT ester with a slightly longer release tail than enanthate. Steady state ~4–5 weeks.
Overview
Testosterone cypionate is the most prescribed injectable testosterone ester in the US, used clinically for hormone replacement therapy (TRT) and off-label as a cycle base. Its roughly 8-day half-life (via the cypionate ester) enables once- or twice-weekly injection, with steady state reached after about 5 weeks. The ester controls the release rate: once injected into the muscle, tissue esterases slowly cleave the cypionate chain, releasing free testosterone that binds the androgen receptor and drives protein synthesis, nitrogen retention, and erythropoiesis. It aromatizes to estradiol and 5-alpha-reduces to DHT, so monitoring total/free testosterone at trough, estradiol, hematocrit, lipids, and PSA is central to harm reduction. Twice-weekly injection smooths the peak-to-trough swing and reduces E2 and hematocrit side effects compared to once-weekly dosing. HPTA suppression is complete and rapid, requiring a structured PCT after any non-TRT use. It is not hepatotoxic since it bypasses first-pass metabolism.
Pharmacokinetic summary
- Model tier
- Linear Regression (sublinear dose)
- Half-life
- 7 days
- Cmax
- 964 ng/dL
- Tmax
- 4.5 days
- Bioavailability
- 70%
- Typical dose
- 100–600 mg
Harm reduction
- Aromatizes
- Yes
- DHT derivative
- No
- Injection frequency
- 2×/week
- Bloodwork range
- 300–1000 ng/dL
Related compounds
Testosterone Enanthate
Long-acting testosterone ester; the most common TRT and cycle base. Reaches steady state in ~5 weeks.
Testosterone Propionate
Short-acting ester with sharp peaks; requires frequent injection. Useful for frontloading.
Testosterone Undecanoate (Castor Oil)
Very long-acting ester (Nebido). Dosed 1000 mg every 10–14 weeks for TRT. NHS standard.
Protocols featuring Testosterone Cypionate
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