A plain-spoken reading room for the semaglutide literature — the oral tablet and the once-weekly shot, side by side, from STEP 1 and SUSTAIN-6 to SELECT, FLOW and SURMOUNT-5.
Pharmacy Semaglutide

Semaglutide Half Life and Pharmacokinetics, Explained

The gist

The semaglutide half life is about one week — roughly 165 to 168 hours. Half-life is just the time it takes for the amount of drug in your blood to fall by half. A one-week half-life is extraordinarily long for a peptide, and it's the entire reason the injection can be given only once a week. It also means the drug clears slowly: it takes roughly five weeks after the last dose for semaglutide to be essentially gone [5].

What makes it last so long? Two design features. First, the molecule resists DPP-4, the enzyme that destroys natural GLP-1 in about two minutes. Second, a fatty-acid tail clamps it onto albumin, a blood protein, so the kidneys can't easily filter it out. Both the tablet and the injection share this same long half-life [5]. Below we explain the pharmacokinetics in plain terms, then what the long tail means in practice. Nothing here is dosing advice.

Why semaglutide lasts about a week

Pharmacokinetics is just the study of what the body does to a drug — how it's absorbed, distributed, and cleared. Native GLP-1 has terrible pharmacokinetics for a medicine: the enzyme DPP-4 (dipeptidyl peptidase-4, a kind of molecular scissors) chops it up within about two minutes. Semaglutide was engineered to fix that.

The first edit blocks the scissors. Swapping the position-8 building block for alpha-aminoisobutyric acid (Aib) makes the spot DPP-4 normally cuts unrecognizable, so the enzyme can't act [5]. The second edit adds a life raft. A long C18 fatty-diacid tail binds reversibly to serum albumin — the most abundant protein in blood — and while semaglutide rides albumin, the kidneys can't filter it out and metabolizing enzymes can't easily reach it [5]. Together these push the half-life from two minutes to about a week. Because the same molecule is in both forms, the tablet and the injection share this ~1-week half-life — the difference between them is absorption, not how long the drug lasts once it's in [8].

What a one-week half-life means in practice

A long half-life has real consequences, and the research spells several out.

Once-weekly dosing. Because levels fall slowly, a weekly injection keeps the drug in a useful range the whole week — no daily peaks and troughs [5].

Slow to clear. It takes roughly five half-lives — about five weeks — for the drug to be essentially gone after the last dose [5]. That's why the literature describes a long washout.

The pregnancy washout. Because clearance is slow, label guidance advises stopping well before a planned pregnancy — commonly cited as roughly two months. The half-life arithmetic is what drives that interval; the contraindication in pregnancy itself is a labeling statement [5].

Steady ramp-up. A long half-life also means it takes several weeks of dosing to reach steady levels, which is part of why trial protocols stepped the dose up gradually [1]. All of this is descriptive pharmacology drawn from the literature, not guidance for any individual.

Half-life: tablet vs injection

Does the route change the half-life? No. The elimination half-life is about one week for both oral and subcutaneous semaglutide, because once the molecule is in your bloodstream it behaves identically regardless of how it got there [5]. What the route changes is the front end — getting in.

The injection delivers about 89% of its dose into circulation. The tablet, even with the SNAC absorption enhancer, delivers only about 0.4-1%, which is why oral doses are far higher in milligrams and why empty-stomach timing matters so much [8]. So the mental model is: two very different front doors (absorption), one identical back door (a ~1-week half-life and a ~5-week washout). For the full route comparison, see the oral semaglutide page; for the cautions tied to the slow washout, see Semaglutide effects.