Testosterone Cypionate
Testosterone ester, injectable. Half-life 6.9 days.
Also called Test C, Test Cyp, Depo-Testosterone
Serum concentration from a single dose
single 100 mg dose over 4.9 weeks, vertical lines mark each half-life elapsed since the peak
What the numbers mean
A 6.9 day terminal half-life, near enough to enanthate that the two plot almost identically on the same schedule. Its 4.5 day time to peak is the slowest of the common testosterone esters, so the rise is visible rather than instant. Ester weight leaves about 70% active testosterone.
The active fraction is the share of each milligram the model treats as reaching circulation as active compound. For an injectable that is ester weight: a milligram of enanthate is not a milligram of testosterone. For an oral it is bioavailability, the share that survives the gut and the liver, which is why some orals sit far below 100%. How the model works.
Where these numbers come from
The half-life and the peak concentration are both read from a published reference. Read it on Translational Andrology and Urology.
The half-life has no strong primary source behind it: the 8 days usually quoted comes from a manufacturer label rather than a published measurement. Combined with the unusually slow rise, that makes this the roughest curve in the testosterone family even though the compound itself is one of the most used.
Common questions about Testosterone Cypionate
What is the half-life of Testosterone Cypionate?
The model uses a terminal half-life of 6.9 days for Testosterone Cypionate. For an injectable that figure is the rate the oil depot releases the compound rather than the rate the body clears it, which is why it runs longer than the half-life of the ester itself.
How long does Testosterone Cypionate take to reach steady state?
Roughly 4.9 weeks, on a schedule that does not change. Steady state is conventionally taken as five half-lives, the point at which each dose is clearing about as fast as the next one arrives, and at a half-life of 6.9 days that puts Testosterone Cypionate at 4.9 weeks of climbing before the curve flattens.
How long does Testosterone Cypionate stay in your system?
About 5.4 weeks after the last dose for the serum level to fall to a few percent of where it was, on the same five-and-a-half half-life reasoning. That is the modelled blood level only. It is not a detection window: metabolites are found by testing long after the parent compound has gone, and this model says nothing about that.
Put Testosterone Cypionate on a timeline with the rest of your cycle and watch the curves add up.
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