Half-Life
The time for blood levels of a drug to fall by half — about a week for semaglutide, which explains nearly everything about its schedule.
Half-life is pharmacology's clock: the interval over which the body clears half of a drug. Semaglutide's is roughly seven days — engineered via albumin binding — which single-handedly explains the weekly schedule, the gentle forgiveness of a slightly late dose, the five-ish weeks effects take to fade after stopping, and the two-month pre-pregnancy washout.
It also sets expectations at both ends of treatment: steady-state levels take four to five half-lives to establish, so the first weeks on any dose understate its eventual effect, and appetite returns gradually rather than overnight after quitting. Tirzepatide runs a similar weekly logic; daily drugs like liraglutide (half-life ~13 hours) show the same math at faster speed.
This glossary entry is general information, not medical advice, and is written to be consistent with FDA prescribing information and primary trial publications as of its last review. Always consult a licensed healthcare provider for personal medical decisions.
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