Half-life is the time it takes for the amount of a drug in the body to fall by half. It is the single number that shapes an estimated level curve, and it is why one GLP-1 drug is taken twice daily and another once weekly. Every value below is quoted from section 12.3 of the product’s FDA label, except retatrutide, which has no label and is quoted from its published phase 1b trial.

The table

Compound	Products	Half-life (hours)	Plain language	Source
Exenatide	Byetta	2.4	Label: mean terminal half-life 2.4 hours; concentrations measurable for about 10 hours after a dose.	[1]
Exenatide extended-release	Bydureon BCise	Not stated as a terminal half-life	Release-controlled microsphere formulation. Label: plasma concentration peaks around Week 6 to 7 after a single dose, and steady state is reached at about Week 10 of weekly use. The slow curve comes from the formulation, not from exenatide itself.	[2]
Lixisenatide	Adlyxin; Soliqua 100/33 (with insulin glargine)	~3	Label: mean terminal half-life approximately 3 hours after multiple doses in type 2 diabetes.	[3][4]
Liraglutide	Victoza, Saxenda	~13	Label: elimination half-life approximately 13 hours, which is why it is a once-daily product.	[5][6]
Dulaglutide	Trulicity	~120 (about 5 days)	Label: elimination half-life approximately 5 days.	[7]
Semaglutide	Ozempic, Wegovy	~168 (about 1 week)	Label: elimination half-life approximately 1 week; drug present in circulation for about 5 weeks after the last dose.	[8][9]
Tirzepatide	Mounjaro, Zepbound	~120 (about 5 days; Zepbound label gives 5–6 days)	Mounjaro label: approximately 5 days. Zepbound label: approximately 5–6 days in adults with overweight or obesity.	[10][11]
Retatrutide	None (investigational)	~144 (about 6 days)	Phase 1b trial in adults with type 2 diabetes: pharmacokinetics dose-proportional, half-life approximately 6 days. Not FDA-approved; cannot be used in compounding under federal law.	[12][13]

Populations: the semaglutide, tirzepatide, liraglutide and lixisenatide values were measured in adults with type 2 diabetes or with overweight or obesity, by the subcutaneous route [3][5][6][8][9][10][11]. Retatrutide’s figure comes from 72 adults with type 2 diabetes in a 12-week study [12].

What the numbers mean for a level curve

A short half-life means a drug rises and falls within the day. Byetta’s exenatide is largely gone about 10 hours after an injection [1]. A long half-life means each dose is layered on top of what is still in the body from the last one. That is why the Ozempic label says semaglutide, with a half-life of about a week, is still present around 5 weeks after the final dose [8].

With regular dosing, the level climbs toward a plateau called steady state. The arithmetic is fixed: after one half-life the level is at 50% of the eventual plateau, after two it is at 75%, after three about 88%, after four about 94%, and after five about 97%. So a weekly semaglutide plan reaches roughly 97% of steady state after about 5 weeks, and a liraglutide plan reaches it in under 3 days. Bydureon BCise is the exception in the table: its label describes steady state at about Week 10 because the microspheres release exenatide slowly, not because exenatide has a long half-life [2].

The same arithmetic runs in reverse after a missed dose or a stop. A drug with a 13-hour half-life is mostly cleared in a few days; one with a 1-week half-life takes about 5 weeks. The Wegovy label uses that fact when it tells patients planning a pregnancy to stop at least 2 months beforehand “because of the long half-life of semaglutide” [9].

How STACK uses these values

STACK’s simulator takes the half-life from this table as the reference value for each compound, applies first-order decay to each dose you log, and adds the overlapping contributions to draw an estimated level curve. Where a label gives a range, STACK uses the single value shown in the hours column and states the range on the compound’s page. For tirzepatide that is 120 hours, with the Zepbound label’s 5–6 days noted [10][11]. For retatrutide it is 144 hours, flagged as investigational and drawn from a phase 1b trial rather than a label [12].

STACK’s curve is an estimate from these published half-lives, not a blood level. It does not know your kidney function, your body weight, your injection technique, or whether a compounded product actually contains what its label says. It cannot measure anything. What it shows is the shape that the published pharmacokinetics predict, so a missed dose, a dose your prescriber moved by a day, or the step-up your prescriber scheduled has a visible consequence on the timeline. Use it to have a better conversation with your prescriber, not to make decisions on your own.

Try it: Level simulator

See how an estimated level builds and decays over weeks from a published half-life and a schedule. An illustration of first-order decay — not a blood level.

Open the level simulator Open STACK on the web

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Sources

Every URL below was fetched and checked on 2026-09-24. Bracketed numbers in the text link here.

GLP-1 half-lives compared