Test E's half-life is about 4.5 days (Behre et al. 1995: terminal elimination half-life of 4.5 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 | 346 mg, 2 days after the last dose |
| 50% of that left | 6.5 days after the last dose |
| 10% of that left | 17 days after the last dose |
| 3% of that left | 25 days after the last dose |
| Levels off | Around day 24.5 |
On the example input, 200 mg twice a week, the curve levels off around day 24.5; after the last dose it takes 17 days to fall to 10% of its final 346 mg peak and 25 days to fall to 3%.
A single 200 mg injection fades on the same timeline from a lower peak of 144 mg of testosterone, because every dose in the model decays at the same 4.5-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 | 436 mg | 202 mg | 54% |
| Twice a week (open in plotter) | 200 mg | 346 mg | 274 mg | 21% |
| Every 3 days (open in plotter) | 171.4 mg | 333 mg | 286 mg | 14% |
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 54% between its high and low point; split into 171.4 mg every 3 days, the swing is 14%.
The chart shows days 70 to 84 of a 12-week run, after all three schedules have levelled off.
Behre et al. 1995 give a terminal elimination half-life of 4.5 days, stated as background in the abstract. The plot uses that figure.
Kaminetsky et al. 2015 measured an apparent half-life of 172.6 hours, about 7.2 days, after 200 mg IM in men who were already on regular injections, so it is a steady-state value from a different design.
The FDA label's 10 to 100 minutes is the half-life of free testosterone in blood, not of the injected depot. The same label says esters in oil are absorbed slowly from the injection site, and that slow absorption is what the plotted curve follows.
No FDA label gives an intramuscular half-life for the enanthate, which is why the data quality is medium rather than high.
| Compound | Half-life | Time to peak | Parent share | Levels off | To 10% after last dose |
|---|---|---|---|---|---|
| Test E | 4.5 days | 2 days | 72% | Day 24.5 | 17 days |
| Test C | 5 days | 2 days | 70% | Day 28 | 18.8 days |
| Test P | 19 hours | 1 day | 84% | Day 5 | 3.8 days |
| Test U | 34 days | 7 days | 63% | Day 210 | 120 days |
Each row uses that compound's own example input. Of these, Test P falls to 10% of its final peak soonest after the last dose (3.8 days), and Test U takes longest (120 days).
The plot uses 4.5 days, the figure from Behre et al. 1995. At that rate the modeled amount falls to half its peak 6.5 days after the last injection, as the washout table shows.
In the model each injection climbs in a straight line to its peak 2 days later, the value in the key numbers table. Kaminetsky et al. 2015 measured a mean of 33.3 hours after 200 mg into the muscle, in men already on regular injections.
On the example input of 200 mg twice a week, the modeled amount levels off around day 24.5. After the last injection it falls to 10% of its final peak in 17 days and to 3% in 25 days. That is drug remaining in the model, not a drug-test window, and the washout table adds the 50% point.
Behre et al. 1995 state 4.5 days as background in an abstract, Kaminetsky et al. 2015 measured about 7.2 days in men already on regular injections, and the FDA label's 10 to 100 minutes is free testosterone in blood rather than the injected depot. The plot uses 4.5 days, and the notes on each source explain why the figures differ.
Data quality: Medium. How the model works.