Half-life simulator

How this model works

Each injection is modeled as an exponential decay starting at 100 relative units and halving every "half-life" period you select. Repeated injections at your chosen interval stack on top of each other, so the simulated curve reaches a higher steady-state range after the first few doses, exactly as real pharmacokinetic accumulation does in principle. The vertical axis is a relative index, not a concentration in any real unit.

Why the ester and interval both matter

A short-acting ester like propionate combined with a long interval produces a sharp peak followed by a steep decline. A long-acting ester like cypionate or undecanoate, or a shorter interval, produces a flatter line with smaller peak-to-trough swings. Neither pattern is universally "better," it is a tradeoff prescribers discuss with individual patients.

What this model leaves out

Real absorption from an intramuscular or subcutaneous depot is not a perfect exponential curve, and it varies by injection site, body composition, and individual metabolism. This tool also does not model oral or transdermal formulations. Treat the shape of the curve as illustrative of the underlying principle, not as a forecast of your own levels.

Frequently asked questions

What does this simulator actually show?

It shows a relative exposure index over time, built from a single-compartment exponential decay model and the dosing interval you choose. It is illustrative pharmacology, not a prediction of your personal serum testosterone level in ng/dL.

Why do different testosterone esters have different half-lives?

Esterification changes how quickly an injected testosterone preparation releases into circulation. A shorter ester like propionate clears faster and produces sharper peaks and troughs, while a longer ester like cypionate or enanthate releases more slowly, producing a flatter curve at a given interval.

Can I use this simulator to predict my own blood levels?

No. Individual absorption, metabolism, and clearance vary significantly between people, and this model does not account for your body weight, injection site, or individual pharmacokinetics. Only a blood draw measures your actual level.

Why does a shorter interval produce a flatter line?

More frequent, smaller injections reduce the size of each peak and trough relative to less frequent, larger injections of the same weekly total, which is why some prescribers favor splitting a weekly dose into two or more injections.