Retatrutide half-life: what the pharmacokinetic data show

What is retatrutide’s half-life?

Approximately six days. The figure comes from the first multiple-dose study in people: a Phase 1b trial in which 72 adults with type 2 diabetes received once-weekly subcutaneous retatrutide, dulaglutide or placebo for 12 weeks (Urva et al., The Lancet, 2022). The authors reported that the pharmacokinetics were dose proportional and that the half-life was approximately 6 days, and the main text gives the half-life as a single approximate value without a range.

The single-dose Phase 1 study reported with the discovery work points the same way: Coskun et al. (Cell Metabolism, 2022) found that the pharmacokinetic profile supported once-weekly dosing and that a reduction in body weight persisted up to day 43 after a single dose.

Why does retatrutide stay in the body longer than natural incretin hormones?

Natural incretin hormones are removed fast. In a classic study, 30 minutes after a subcutaneous injection of native GLP-1 the breakdown product already made up about four-fifths or more of the added circulating GLP-1-related material: 78% in healthy volunteers and 89% in people with type 2 diabetes (Deacon et al., Diabetes, 1995).

Retatrutide is built to last longer. It is a 39-amino-acid peptide conjugated to a C20 fatty diacid, and the Phase 1b authors describe it as having an extended pharmacokinetic half-life. The labels of the two approved drugs built on the same principle explain the mechanism: the fatty diacid binds reversibly to albumin, which lowers kidney clearance and protects against breakdown (semaglutide, UK label), and tirzepatide, which also carries a C20 fatty diacid, is 99% bound to albumin (UK label). For retatrutide the albumin-bound fraction has not been published, so the mechanism is inferred from its structure rather than measured. Structure and receptor activity are covered on the mechanism of action page.

How does retatrutide’s half-life compare with tirzepatide and semaglutide?

All three have half-lives in the range of five to seven days. The table sets out what the UK labels and the published retatrutide trial report. Where a retatrutide figure has not been published, the cell says so.

Because the numbers come from different studies, small differences should not be read as a ranking. The receptor and structural differences between the three compounds are covered in the three-way comparison.

How long does it take to reach steady state, and how long does retatrutide stay in the body?

Neither has been reported for retatrutide. The figures below are standard first-order pharmacokinetic arithmetic applied to the published six-day half-life. They are calculations, not measurements.

• Washout. The amount in the body halves every half-life. After five half-lives, about 30 days, roughly 3% of a dose remains.
• Steady state. With weekly injections, levels build for about four to five half-lives, roughly 24 to 30 days, before the pattern repeats from week to week.
• Accumulation. With a six-day half-life and a seven-day interval, exposure at steady state is about 1.8 times that after a first injection.

The labels for the approved drugs are consistent with this arithmetic. Tirzepatide’s UK label says steady-state exposure is reached after 4 weeks of once-weekly use, and the semaglutide labels say the drug stays in the circulation for about 5 weeks (US Ozempic label) or about 7 weeks (UK Wegovy label, 2.4 mg dose) after the last dose.

How does exposure change with dose?

In the Phase 1b trial, peak concentration and total exposure rose approximately in proportion to dose across the range studied, up to 12 mg once weekly. The registry entry for the Phase 2 diabetes trial (NCT04867785) adds model-based estimates of average steady-state concentration by dose arm. Dividing each estimate by its weekly dose gives a similar number in every arm, which is what proportional exposure looks like.

What is still unknown about retatrutide’s pharmacokinetics?

Semaglutide and tirzepatide have labels that report absorption, distribution and elimination in detail. The public record on retatrutide is thinner. The retatrutide papers and registry results reviewed for this page (the discovery paper at abstract level only) do not report:

• clearance or volume of distribution;
• the albumin-bound fraction or absolute bioavailability;
• whether body weight, sex, age, kidney function or liver function changes exposure;
• interactions with other medicines;
• how the drug is broken down and excreted.

Eli Lilly has registered completed Phase 1 studies on most of these questions. None of the 9 in the table has posted results on the registry, and no peer-reviewed report of any of them was found in PubMed or Europe PMC on 16 October 2026. Registry checked 15 October 2026.

How were these figures checked?

The half-life, time to peak and dose-proportionality statements were read in the text of the Phase 1b paper; the single-dose study was read at abstract level only. The steady-state concentrations are the values posted on the ClinicalTrials.gov record. Semaglutide and tirzepatide figures are from the UK and US labels as published on 16 October 2026. Calculations are ours and are marked as calculations. Retatrutide is an investigational compound and none of this is dosing or usage guidance.