Testosterone cypionate is the cypionate ester of testosterone — an 8-carbon ester attached at the C-17 hydroxyl that slows hydrolysis and extends half-life to approximately 8 days after intramuscular or subcutaneous injection. It is the most widely used testosterone preparation for testosterone replacement therapy (TRT) research and the standard reference compound for androgen receptor (AR) biology studies requiring sustained, physiologically relevant testosterone exposure. Research applications include HPG axis biology, muscle hypertrophy mechanisms, erythropoiesis, bone density, body composition, cardiometabolic effects of androgen, and testosterone deficiency (hypogonadism) models.
8 days
Half-life — bi-weekly or weekly dosing
412.6
Molecular weight g/mol
AR agonist
Androgen receptor — full agonist
HPG axis
Testosterone → LH/FSH feedback
≥99%
Purity — analytical grade
Testosterone Cypionate — Specifications
Testosterone Cypionate — specifications
Property
Value
CAS Number
58-20-8
Molecular Formula
C₂₇H₄₀O₃
Molecular Weight
412.6 g/mol
Half-life
~8 days (IM/SC)
Class
Androgen / Anabolic steroid (ester)
Purity
≥99% HPLC verified
COA
Janoshik independent third-party
⚙️
Mechanism of Action — Testosterone Cypionate
Testosterone cypionate is hydrolysed by esterases to free testosterone within 24–72 hours of injection. Free testosterone exerts its effects through:
Androgen receptor (AR) — direct: Nuclear receptor → gene transcription. Key targets: muscle protein synthesis (MPS) genes (Myosin heavy chain, IGF-1, PCNA), bone mineral density (osteoblast activation), erythropoiesis (EPO upregulation in kidney)
DHT conversion: 5α-reductase → dihydrotestosterone (DHT) — higher AR affinity. Dominant in prostate, skin, CNS
HPG axis feedback: Testosterone → hypothalamus (GnRH suppression) + anterior pituitary (LH/FSH suppression). Foundation of TRT-induced HPG suppression research
Non-genomic: Rapid membrane AR signalling — Akt/mTOR activation, Ca2+ flux in muscle and cardiac tissue
HPG axis suppression — the core TRT research variable
Exogenous testosterone suppresses hypothalamic GnRH and pituitary LH/FSH via negative feedback — reducing endogenous testicular testosterone production and spermatogenesis. This suppression is dose-dependent and time-dependent. Research studies the rate of suppression, recovery kinetics post-cessation, and interventions (HCG, SERMs, GnRH analogs) to maintain testicular function during exogenous androgen exposure. QSC’s HCG product is the standard co-administration compound for HPG axis preservation studies.
Key Research Studies & Clinical Data
Key testosterone research studies
Study
Design
Key finding
Bhasin et al. 2001 (NEJM)
61 healthy men, graded T doses, 20 weeks
Dose-dependent increases in muscle mass, strength, fat-free mass — established dose-response relationship
TRT-USA Trial 2016
790 hypogonadal men, T gel vs placebo, 1 year
Improved sexual function, walking distance, bone density, mood vs placebo
TRAVERSE 2023 (NEJM)
5246 hypogonadal men, 40-mo follow-up, CV safety
Non-inferior to placebo for MACE — resolved long-standing CV risk debate
Xu et al. 2013 (BMJ meta-analysis)
75 trials, testosterone and cardiovascular
Heterogeneous CV risk — framework for ongoing research
Research Protocols — Testosterone Cypionate
Protocol 1: Hypogonadism model (orchidectomised rat)
Bilateral orchidectomy → 2-week recovery → testosterone cypionate 5–20 mg/kg IM once weekly × 6 weeks. Endpoints: body composition (lean/fat mass), bone density (DXA/µCT), muscle weight (gastrocnemius, levator ani), HPG hormones (LH, FSH, E2), haematocrit, prostate weight.
Protocol 2: Muscle hypertrophy (intact male)
Testosterone cypionate 10 mg/kg IM weekly × 8 weeks in intact male rats. MPS (SUnSET puromycin assay), myosin heavy chain isoforms (WB), satellite cell count (IHC), mTOR/Akt/S6K1 signalling, grip strength.
Protocol 3: TRT + HCG HPG preservation
Testosterone cypionate 10mg/kg + HCG 10 IU SC 3×/week vs T alone in orchidectomised rats. Testicular weight, intratesticular testosterone, Leydig cell morphology (EM), spermatogenesis (histology).
Protocol 4: Erythropoiesis
Testosterone cypionate at TRT doses in rats. Haematocrit, haemoglobin, reticulocyte count, renal EPO mRNA (qPCR), BFU-E/CFU-E colony formation from bone marrow.
What is testosterone cypionate used for in research?
Testosterone cypionate is the standard androgen for HPG axis, muscle hypertrophy, erythropoiesis, bone density, and TRT pharmacology research. Its 8-day half-life allows once-weekly or bi-weekly dosing in animal models, producing stable androgen exposure equivalent to TRT protocols in humans.
What is the difference between testosterone cypionate and testosterone enanthate?
Both are testosterone esters with similar half-lives (cypionate ~8 days, enanthate ~7 days) and identical androgenic activity once hydrolysed. Cypionate uses a C-8 ester (cypionate/cyclopentylpropionate); enanthate uses a C-7 ester. Pharmacologically equivalent for most research purposes. Cypionate is more common in US research; enanthate in European research.
How does exogenous testosterone suppress the HPG axis?
Exogenous testosterone acts on hypothalamic GnRH neurons and pituitary gonadotrophs via negative feedback, suppressing GnRH pulse frequency and LH/FSH secretion. This reduces testicular Leydig cell stimulation → reduced endogenous testosterone and Sertoli cell stimulation → reduced spermatogenesis. The suppression is dose-dependent and typically complete within 3-4 weeks of TRT-dose administration.
What formats does QSC supply testosterone cypionate in?
QSC supplies testosterone cypionate at 250 mg/mL in 10mL vials — available as 10-vial kits (100mL) or 20-vial kits (200mL). Ships from domestic QSC warehouses in USA, EU, UK, Canada, and Australia.
Is testosterone cypionate the same as the pharmaceutical product?
The pharmaceutical product (e.g., Depo-Testosterone) is FDA-approved for human TRT. QSC testosterone cypionate is research-grade material of ≥99% purity confirmed by HPLC — supplied for laboratory research purposes only. Not for human use.
Research Use Only: All QSC compounds are sold strictly for laboratory research purposes. Not for human use. Not approved by the FDA or equivalent regulatory bodies for human administration. All purchases confirm research intent and compliance with applicable local regulations.
