Published figures for Test C's half-life disagree; the plot uses about 5 days.
Half-life estimate, not bloodwork or dosing advice. Disclaimer.
By Austin Witherow and Mason Calvert · Last updated · Sources
| Measure | 200 mg twice a week, after the last dose |
|---|---|
| Highest amount | 364 mg, 2 days after the last dose |
| 50% of that left | 7 days after the last dose |
| 10% of that left | 18.8 days after the last dose |
| 3% of that left | 27.5 days after the last dose |
| Levels off | Around day 28 |
On the example input, 200 mg twice a week, the curve levels off around day 28; after the last dose it takes 18.8 days to fall to 10% of its final 364 mg peak and 27.5 days to fall to 3%.
A single 200 mg injection fades on the same timeline from a lower peak of 140 mg of testosterone, because every dose in the model decays at the same 5-day half-life.
This is the modeled amount of the drug itself. Drug tests look for metabolites and use different, often longer, windows. Pedplot does not estimate detection times.
| Frequency | Each dose | High point | Low point | Swing |
|---|---|---|---|---|
| Weekly (open in plotter) | 400 mg | 451 mg | 225 mg | 50% |
| Twice a week (open in plotter) | 200 mg | 364 mg | 296 mg | 19% |
| Every 3 days (open in plotter) | 171.4 mg | 353 mg | 307 mg | 13% |
Each schedule name opens that curve in the plotter.
The example input adds up to 400 mg a week. Given once a week as one 400 mg injection, the modeled amount swings 50% between its high and low point; split into 171.4 mg every 3 days, the swing is 13%.
The chart shows days 70 to 84 of a 12-week run, after all three schedules have levelled off.
The Depo-Testosterone FDA label says testosterone cypionate injected into the muscle has a half-life of approximately eight days.
Bi et al. 2018 fitted a population model to 31 healthy men on 14 weekly injections of 100, 250 or 500 mg, and report a median half-life of 4.05 days for total testosterone. The same paper cites a mean of 6.9 days from an earlier noncompartmental analysis, which was not read for this page.
With a depot in oil, a one-compartment model like Bi's cannot fully tell slow absorption from elimination, so its half-life and the label's are not measuring quite the same step.
The plot keeps 5 days, between the label and Bi's median, and takes the time to peak from Bi's model parameters: about 1.8 days, drawn as 2. No source gives 5 days itself, which is why the data quality is low.
The label's eight days would make cypionate a little longer-acting than enanthate; Bi's 4.05 days would not.
| Compound | Half-life | Time to peak | Parent share | Levels off | To 10% after last dose |
|---|---|---|---|---|---|
| Test C | 5 days | 2 days | 70% | Day 28 | 18.8 days |
| Test E | 4.5 days | 2 days | 72% | Day 24.5 | 17 days |
| Test U | 34 days | 7 days | 63% | Day 210 | 120 days |
| Sustanon | 7.5 days | 3 days | 70% | Day 42 | 23.5 days |
Each row uses that compound's own example input. Of these, Test E falls to 10% of its final peak soonest after the last dose (17 days), and Test U takes longest (120 days).
The plot uses 5 days, a value no single source gives. The Depo-Testosterone label gives approximately eight days and Bi et al. 2018 a median of 4.05 days, and the plot sits between them. At that rate the modeled amount falls to half its peak 7 days after the last injection, as the washout table shows.
In the model each injection peaks 2 days after it is given, and the example input of 200 mg twice a week levels off around day 28, as the washout table shows. The time to peak comes from Bi et al. 2018, whose model parameters give about 1.8 days.
Test C has a half-life of 5 days against 4.5 days for Test E, so Test C is the longer-acting of the two in the model. Per mg, Test C is 70% testosterone and Test E 72% testosterone. On their own example inputs, Test C falls to 10% of its final peak 18.8 days after the last dose and Test E 17 days, as the comparison table shows. On paper it depends on the source: the Depo-Testosterone label's eight days would make cypionate the longer of the two, and Bi et al. 2018's 4.05 days would not.
About 69.9 mg of every 100 mg is testosterone: PubChem lists 288.4 for testosterone and 412.6 for the ester. So the default 200 mg injection is drawn as 140 mg of testosterone, as the ester arithmetic shows.
Data quality: Low. How the model works.