Testosterone cypionate

Testosterone cypionate is a long-acting esterified form of testosterone, the primary endogenous androgen in males. Esterification at the 17-beta position with cypionate (cyclopentylpropionate) increases lipid solubility and creates a depot effect following intramuscular or subcutaneous injection — testosterone is released gradually as the ester is cleaved by esterases in muscle and blood, producing sustained physiological testosterone concentrations from a single injection. The cypionate ester produces peak plasma testosterone concentrations within 24–48 hours and an effective duration of action of approximately 7–10 days, although clinical practice varies in injection frequency.¹

Testosterone is an endogenous steroid hormone responsible for the development and maintenance of male secondary sexual characteristics, spermatogenesis, libido, erythropoiesis, bone density, lean body mass, and metabolic function. Testosterone cypionate injection is one of the most commonly prescribed testosterone formulations in the United States and is frequently the vehicle for testosterone replacement therapy (TRT).

Testosterone cypionate is a Schedule III controlled substance under the federal Controlled Substances Act.

Testosterone cypionate injection is indicated for replacement therapy in males with conditions associated with deficiency or absence of endogenous testosterone:¹

• Primary hypogonadism (congenital or acquired): Testicular failure due to cryptorchidism, bilateral torsion, orchitis, vanishing testis syndrome, or orchidectomy.
• Hypogonadotropic hypogonadism (congenital or acquired): Gonadotropin or LHRH deficiency, or pituitary-hypothalamic injury from tumors, trauma, or radiation.

Important off-label use disclosure: The FDA label explicitly states that "Safety and efficacy of Testosterone Cypionate Injection in men with 'age-related hypogonadism' (also referred to as 'late-onset hypogonadism') have not been established." The widespread use of testosterone in men experiencing age-related declines in testosterone without structural or genetic hypogonadism is therefore off-label, and clinicians and patients should understand this distinction.¹

Testosterone has also been used off-label as part of gender-affirming hormone therapy for transgender men and non-binary individuals.

For replacement therapy in hypogonadal males, the FDA label documents a dosing range of 50 to 400 mg administered every 2 to 4 weeks.¹ Clinical practice has evolved considerably from this labeling — many prescribers now use smaller, more frequent injections (for example, 100–200 mg administered weekly or biweekly, or 50–100 mg administered two to three times per week) to avoid the supraphysiologic peak and symptomatic trough that occur with the traditional 2–4 week cycle. Subcutaneous injection of smaller volumes is also used off-label by some practitioners as an alternative to intramuscular injection.

Dosing is individualized based on clinical response, symptom control, and laboratory monitoring of total and free testosterone, hematocrit, and lipid parameters.

Real-world practice: Many users on TRT split their weekly dose into two equal injections administered every 3.5 days (e.g. 75mg twice weekly from a 150mg weekly prescription) to maintain more stable serum testosterone levels and reduce the peak-to-trough fluctuation associated with once-weekly dosing. Some protocols use even more frequent dosing (e.g. every 4 days). Volume per injection depends on the concentration of the vial — a common concentration is 200mg/mL, so 150mg weekly = 0.75mL weekly = 0.375mL per injection twice weekly. Always follow your prescribing physician's specific schedule.

Intramuscular injection (labeled route). Subcutaneous injection is frequently used in practice for smaller, more frequent doses (off-label route).

Store at controlled room temperature (68°F to 77°F / 20°C to 25°C). Protect from light. Testosterone cypionate injection may form crystals at low temperatures; warming and gently shaking the vial will redissolve crystals. Multi-dose vials are available.¹

Testosterone cypionate carries the general warnings and considerations applicable to androgen therapy:¹

• Erythrocytosis (polycythemia): Testosterone stimulates erythropoiesis. Elevated hematocrit — a common effect of TRT — increases blood viscosity and may raise thromboembolic risk. Hematocrit monitoring is a standard component of TRT management; dose reduction, donation of blood, or temporary discontinuation may be needed.
• Cardiovascular risk: A 2024 randomized controlled trial (the TRAVERSE study) that specifically enrolled men with hypogonadism and elevated cardiovascular risk found no significant increase in major adverse cardiovascular events with testosterone versus placebo, but did observe a higher incidence of nonfatal cardiac arrhythmias, deep vein thrombosis, and pulmonary embolism in the testosterone group. The cardiovascular risk profile of testosterone therapy, particularly in higher-risk populations, remains an active area of clinical research.
• Suppression of spermatogenesis / infertility: Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis, substantially reducing or eliminating sperm production. This effect is generally reversible on discontinuation but the timeline to recovery varies. Men who desire future fertility should discuss alternatives (such as human chorionic gonadotropin, clomiphene, or other approaches) with a reproductive endocrinologist.
• Prostate effects: Testosterone stimulates prostatic tissue. Use with caution in men with benign prostatic hypertrophy causing urinary symptoms; testosterone is contraindicated in men with known or suspected prostate cancer. PSA monitoring is a standard element of TRT follow-up.
• Lipid effects: TRT may reduce HDL cholesterol; lipid monitoring is appropriate.
• Acne, oily skin, mood, sleep apnea: These are commonly reported effects; severity varies by individual.
• Misuse and abuse: The label documents that testosterone is subject to misuse and abuse, including by athletes at supratherapeutic doses and in combination with other anabolic-androgenic steroids. Misuse at high doses carries risks of serious adverse cardiovascular, hepatic, and psychiatric events.