Retatrutide Half-Life: What Phase 1 Data Show

The half-life of retatrutide in humans is about 6 days. That figure comes from a 12-week phase 1b multiple-ascending-dose trial in adults with type 2 diabetes, which also found dose-proportional pharmacokinetics (Urva et al., 2022). A half-life of this length is what allows once-weekly administration in clinical trials, and it is achieved through lipidation and albumin binding.

For laboratory research use only. The compounds discussed are not approved for human or veterinary use and are not drugs, foods or cosmetics. This article summarises published research and is not medical advice.

Key points

Half-life ≈ 6 days (phase 1b, type 2 diabetes).
Pharmacokinetics were dose-proportional across the doses studied.
After a single dose in phase 1, effects on body weight persisted up to day 43.
Comparable with tirzepatide (~5 days) and semaglutide (~1 week).
Half-life in the body is unrelated to the shelf stability of research material.

Where the 6-day figure comes from

Study detail	Value
Design	Phase 1b, randomised, double-blind, placebo-controlled, multiple ascending dose
Participants	72 adults with type 2 diabetes (HbA1c 7.0–10.5%), four US centres
Duration	12 weeks, once-weekly administration
Comparators	Placebo and dulaglutide
PK finding	Dose-proportional; half-life ≈ 6 days
Most common adverse events	Gastrointestinal
Reference	Urva et al., 2022

The earlier single-ascending-dose study, reported in the discovery paper, 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 (Coskun et al., 2022).

Why the half-life is so long

Native incretin hormones are cleared within minutes. GLP-1, for example, is rapidly inactivated by dipeptidyl peptidase-4 and cleared by the kidneys (Müller et al., 2019). Long-acting analogues solve this with two strategies:

Strategy	Effect
Non-natural residues near the N-terminus (e.g. Aib)	Resist DPP-4 cleavage
Fatty acid side chain	Reversible binding to serum albumin (~66 kDa), which keeps the peptide out of renal filtration and protects it from proteases

Semaglutide’s discovery illustrates the second point: increasing albumin affinity through the fatty acid and linker was the key to once-weekly exposure (Lau et al., 2015). Retatrutide uses the same general approach.

Comparison with related peptides

Peptide	Receptors	Human half-life	Source
Native GLP-1	GLP-1R	Minutes	Müller et al., 2019
Semaglutide	GLP-1R	~1 week	Clinical pharmacology data
Tirzepatide	GIPR, GLP-1R	~5 days	Schneck et al., 2024
Retatrutide	GIPR, GLP-1R, GCGR	~6 days	Urva et al., 2022

What the half-life implies

Basic pharmacokinetic principles help interpret the number:

Time to steady state: about 4–5 half-lives, so roughly 4–5 weeks with regular weekly exposure.
Washout: similarly, about 4–5 half-lives for concentrations to fall to a few percent of steady state. This matters when planning crossover or washout periods in study design.
Accumulation: with weekly exposure and a 6-day half-life, concentrations accumulate before plateauing; dose escalation in trials partly reflects this.

Half-life versus vial stability

A long biological half-life does not make retatrutide stable on the bench. In the body, albumin binding shields the peptide; in a vial of reconstituted research material, there is no albumin, and degradation depends on temperature, pH, light and handling. Lipidated peptides can also self-associate in solution. Store reconstituted material at 2–8 °C, avoid freeze–thaw and date the vial. See how to reconstitute retatrutide and storing reconstituted peptides.

Our retatrutide research peptide is supplied as lyophilized powder with lot-level HPLC and MS data. For concentration calculations, use the peptide reconstitution calculator.

Open questions

How does retatrutide’s half-life vary with body size, renal function or hepatic function? Population pharmacokinetic analyses of the phase 3 program will answer this more precisely than the phase 1b study could.
Do the three receptor activities persist in the same proportion as concentrations fall? Receptor occupancy over the dosing interval has not been reported in detail.
How quickly does research-grade retatrutide degrade in unbuffered solution? No stability study of reconstituted research material has been published.

When planning experiments, the 6-day figure is best treated as an approximate population value from a single early-phase study, not a fixed constant.

Related research

Frequently asked questions

What is the half-life of retatrutide?

About 6 days. A phase 1b multiple-ascending-dose trial in adults with type 2 diabetes reported dose-proportional pharmacokinetics and a half-life of approximately 6 days.

Why does retatrutide have such a long half-life?

Like other once-weekly incretin peptides, retatrutide is lipidated. The fatty acid binds serum albumin, which protects the peptide from rapid renal clearance and enzymatic degradation.

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

They are in the same range: tirzepatide about 5 days and semaglutide about one week, versus about 6 days for retatrutide.

How long does it take to reach steady state?

As a rule of pharmacokinetics, steady state is approached after about four to five half-lives. For a 6-day half-life, that corresponds to roughly four to five weeks of regular weekly exposure.

Does a long half-life mean retatrutide is stable in solution?

No. Half-life describes clearance in the body. Stability of reconstituted research material depends on temperature, solvent, pH and handling, and must be considered separately.

References

Urva S, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet. 2022. PMID: 36354040 https://pubmed.ncbi.nlm.nih.gov/36354040/
Coskun T, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metab. 2022. PMID: 35985340 https://pubmed.ncbi.nlm.nih.gov/35985340/
Schneck K, et al. Population pharmacokinetics of the GIP/GLP receptor agonist tirzepatide. CPT Pharmacometrics Syst Pharmacol. 2024. PMID: 38356317 https://pubmed.ncbi.nlm.nih.gov/38356317/
Lau J, et al. Discovery of the Once-Weekly Glucagon-Like Peptide-1 (GLP-1) Analogue Semaglutide. J Med Chem. 2015. PMID: 26308095 https://pubmed.ncbi.nlm.nih.gov/26308095/
Müller TD, et al. Glucagon-like peptide 1 (GLP-1). Mol Metab. 2019. PMID: 31767182 https://pubmed.ncbi.nlm.nih.gov/31767182/