What it is. A compound's half-life is the time it takes for the amount in your blood to fall by half. If something has a 24-hour half-life, half is left after one day, a quarter after two, an eighth after three, and so on. It is the single most useful number for understanding how a compound behaves in the body over time.
Accumulation & steady state. If a dose repeats before the previous one clears, the leftovers stack. With regular dosing, levels climb until the amount going in each interval equals the amount cleared - "steady state." Reaching it takes about 4-5 half-lives. A long half-life builds slowly to a smooth, steady level; a short one is fast-on, fast-off, with much bigger peaks and troughs.
Why stability matters for side-effects. Many side-effects track the extremes, not the average - the peak right after a dose (too much, too fast) and the crash at the trough (levels dropping off). Holding a compound in a steady band, instead of letting it spike and dip, is generally how people try to keep side-effects down. Splitting the same weekly amount into smaller, more frequent doses lowers the peak-to-trough swing without changing the average - the same total, a flatter line.
How fast you can stabilize. Because it takes 4-5 half-lives to settle, a long-half-life compound can take weeks to reach a stable level - which is why some protocols use a larger early "loading" dose to get there sooner instead of waiting for it to build. A short-half-life compound stabilizes quickly but needs frequent dosing to stay there. The moving-average overlay and the peak:trough readout in this tool show how steady any given pattern actually is.
Washout & interactions. Half-life also sets how long a compound lingers after the last dose (~4-5 half-lives to clear), and because it governs timing, it shapes how compounds overlap when combined and how long effects and side-effects persist. Two compounds at the same dose can behave completely differently if their half-lives differ.
Important: published half-lives are estimates that vary with the individual (genetics, body composition, liver and kidney function), the formulation, and the route. Treat every curve here as an illustration, not a precise prediction, and not medical advice.
Compound profiles, half-life explainers, deep dives and member discussion, inside the Skool community.
Log side effects as they happen. Each entry drops a numbered marker on the charts at the day it occurred, anchored to the Start date and window you set in the Simulation window panel, so you can see what your modeled levels were doing when it showed up. Saved only in this browser, never uploaded.