Testosterone Cypionate vs. Enanthate: Peak and Trough Profiles
Testosterone cypionate and testosterone enanthate have essentially identical pharmacokinetic profiles with no clinically meaningful difference in peak timing or trough levels. Both formulations reach supraphysiological peak concentrations 2-5 days (specifically 8-24 hours in some studies) after intramuscular injection and return to baseline by days 10-14, making them functionally interchangeable. 1, 2, 3
Pharmacokinetic Equivalence
Both esters produce identical peak timing: Serum testosterone peaks occur 2-5 days post-injection for both cypionate and enanthate, with some studies showing peaks as early as 8-24 hours after administration. 2, 3
Trough timing is the same: Both formulations return to baseline testosterone levels by days 13-14 after a single injection, though one older study suggested enanthate may have a slightly shorter duration (9 days vs. 7 days), which is not clinically significant. 2, 3, 4
Supraphysiological peaks are universal: Both preparations cause testosterone levels to rise 3-5 times above baseline shortly after injection, with many patients achieving concentrations above the normal male range between days 2-7. 2, 3
Clinical Dosing Implications
Weekly dosing (50-100 mg) provides more stable levels than biweekly administration (100-200 mg every 2 weeks) for both formulations, reducing the amplitude of peak-to-trough fluctuations. 1
Biweekly dosing at 200 mg causes wide hormonal swings: Studies show that 200 mg every 14 days results in supraphysiological peaks followed by return to hypogonadal levels by day 13-14, creating suboptimal stability. 2, 4
Target mid-cycle testosterone levels of 450-600 ng/dL should be measured midway between injections (day 7 for biweekly dosing, day 3-4 for weekly dosing) for both cypionate and enanthate. 1
Adverse Effect Profile (Identical for Both Esters)
Erythrocytosis risk is 43.8% with intramuscular injections (both cypionate and enanthate), significantly higher than the 15.4% risk with transdermal preparations, driven by supraphysiological peak testosterone levels. 1
Estradiol elevation occurs with both formulations: The threefold rise in estradiol (days 2-7 post-injection) is a consequence of aromatization during peak testosterone concentrations and occurs equally with cypionate and enanthate. 2
Cardiovascular risk may be higher with injectable formulations compared to transdermal preparations, possibly due to fluctuating testosterone levels rather than any difference between the two injectable esters. 1
Common Pitfalls to Avoid
Do not assume cypionate has a longer duration than enanthate: This is a common misconception; both have essentially identical half-lives and clinical duration of action. 1, 3
Do not use 10-day injection intervals: A 10-day schedule prevents full trough levels from being reached, maintaining more frequent supraphysiologic peaks and increasing erythrocytosis risk up to 44%. 1
Do not measure testosterone at peak (days 2-5): Levels should be checked midway between injections to guide dosing adjustments, not at peak when supraphysiological values are expected. 1, 2