Half-Life and Steady State for Dosing
Half-life is the time for the amount of a compound in your body to fall by half. A compound reaches about 97% of steady state after roughly five half-lives, regardless of how often you dose. Longer half-lives relative to the dosing interval mean more accumulation and a slower approach to a stable level.
For educational and research purposes only. Not medical advice. Always consult a licensed healthcare professional before starting any protocol.
What half-life tells you
Half-life is the time it takes for the amount of a compound in the body to drop by half. Semaglutide has a half-life of about seven days, which is why it is dosed once weekly; a short-acting peptide might have a half-life measured in minutes or hours and needs more frequent dosing to maintain levels.
Half-life drives two practical questions: how long until levels stabilise when you start, and how long until they clear when you stop.
Reaching steady state
When you dose repeatedly, the compound accumulates until the amount you take each interval matches the amount your body clears. That balance point is steady state. It takes roughly five half-lives to reach about 97% of steady state, no matter how frequently you dose. For a seven-day half-life that is about five weeks; for a two-hour half-life it is about ten hours.
The accumulation ratio describes how much higher the steady-state peak is compared with a single dose. Dosing frequently relative to the half-life produces more accumulation, so a long-acting weekly compound builds up far more than a short-acting one dosed daily.
Clearing after the last dose
The same arithmetic works in reverse. After your final dose, levels fall by half every half-life, so about five half-lives later roughly 97% has cleared. A seven-day half-life compound is largely gone about five weeks after the last injection, while a short-acting peptide washes out within hours. The half-life and steady-state estimator models this build-up and washout so you can see the curve for a given dose and interval.
Frequently asked questions
How long does it take to reach steady state?
About five half-lives to reach roughly 97% of steady state, regardless of dosing frequency. For a seven-day half-life that is about 35 days; for a two-hour half-life it is about ten hours.
What is the accumulation ratio?
It is how much higher your steady-state peak is versus a single dose. Dosing often relative to the half-life increases accumulation, so long-acting compounds accumulate more than short-acting ones.
How long until a compound clears after I stop?
Levels halve every half-life, so roughly five half-lives after the last dose about 97% has cleared. A seven-day half-life compound is largely gone in about five weeks.
Are published half-life values exact?
No. Half-lives vary between individuals and sources, and many research peptides have limited data. Treat them as estimates and adjust when you have better information.