Investigational · not FDA approved

Editorially reviewed · Last updated July 2026 · How we review

Retatrutide Half-Life and Pharmacokinetics

Key findings

Retatrutide stays in the body for about six days per half-life, which supports once-weekly dosing and means dose changes take several weeks to fully settle.
Blood levels peak roughly 12–72 hours after an injection and reach a steady pattern after about four to five weeks.
Most of a dose is expected to clear over roughly a month, not in the week after an injection.
Its half-life is close to semaglutide (~7 days) and tirzepatide (~5 days); receptor activity, not half-life alone, explains their different effects.

Retatrutide Half-Life and Pharmacokinetics

Retatrutide has a half-life of approximately 6 days, enabling once-weekly dosing. This is achieved through a fatty diacid conjugation that promotes albumin binding — the same class of engineering used by semaglutide (~7-day half-life) and tirzepatide (~5-day half-life).

This article covers what the Phase 1 data shows about how retatrutide moves through the body, how long it lasts, and how it compares to other GLP-1 drugs.

Key Pharmacokinetic Numbers

Parameter	Value
Half-life	~6 days (144 hours)
Time to peak (Tmax)	12–72 hours after injection
Dosing frequency	Once weekly (subcutaneous)
Time to steady state	~4–5 weeks of weekly dosing
Dose proportionality	Yes — linear PK across tested doses
Route	Subcutaneous injection

Data from the Phase 1 single-ascending-dose study in healthy volunteers and the Phase 1b multiple-ascending-dose study in adults with type 2 diabetes.

How Once-Weekly Dosing Is Achieved

Native GLP-1 hormone has a half-life of only 2 minutes — it is rapidly broken down by the DPP-4 enzyme. Retatrutide extends this to 6 days through three key molecular modifications:

Fatty Diacid Conjugation

Retatrutide is a 39-amino-acid peptide conjugated to a C20 fatty diacid at position K4 (lysine-4), connected through an AEEA spacer and gamma-glutamic acid linker. This fatty acid chain binds non-covalently to serum albumin in the bloodstream, which:

Protects the peptide from enzymatic degradation
Creates a circulating reservoir — the drug slowly releases from albumin into the free (active) form
Slows renal clearance — the albumin-drug complex is too large for kidney filtration
Provides sustained release — free retatrutide is continuously replenished from the albumin-bound pool

DPP-4 Resistance

An alpha-amino isobutyric acid (Aib) residue at position 2 makes retatrutide resistant to cleavage by the DPP-4 enzyme, which would otherwise degrade it within minutes.

Optimized Receptor Binding

An Aib residue at position 20 optimizes GIP receptor activity and the pharmacokinetic profile. Alpha-methyl-L-leucine at position 13 promotes optimal binding across all three receptors.

Absorption and Distribution

After subcutaneous injection, retatrutide is absorbed through local blood vessels and the lymphatic system at the injection site. The albumin-binding fatty diacid ensures slow, sustained absorption.

Peak concentration (Tmax): 12–72 hours post-dose in healthy volunteers; 12–48 hours (median) in adults with type 2 diabetes
Dose proportionality: Plasma concentrations, AUC, and Cmax increase proportionally with dose — dose adjustments produce predictable changes in drug levels
Steady state: Reached after approximately 4–5 weeks of consistent weekly dosing (4–5 half-lives), which is why the clinical titration schedule uses 4-week intervals at each dose level

Metabolism and Elimination

Retatrutide is primarily eliminated through proteolytic degradation, consistent with other peptide drugs. The liver and kidneys both contribute to the elimination process. Importantly, retatrutide does not interact with cytochrome P450 enzymes, which means it has minimal risk of drug-drug interactions through that pathway.

Half-Life Comparison: Triple vs Dual vs Single Agonist

Drug	Mechanism	Half-Life	Fatty Acid	Steady State
Semaglutide (Wegovy/Ozempic)	GLP-1 mono-agonist	~7 days (168 h)	C18 fatty acid	~4–5 weeks
Retatrutide	GLP-1/GIP/Glucagon triple agonist	~6 days (144 h)	C20 fatty diacid	~4–5 weeks
Tirzepatide (Mounjaro/Zepbound)	GLP-1/GIP dual agonist	~5 days (120 h)	C20 fatty acid	~4 weeks

All three drugs use fatty acid acylation to achieve albumin binding and extended half-lives suitable for once-weekly dosing. The pharmacokinetic profiles are broadly comparable — the clinical efficacy differences between these drugs are driven by receptor pharmacology (triple vs dual vs mono agonism), not by pharmacokinetic differences.

What the Phase 1 Data Showed

Phase 1 Single-Ascending-Dose Study (Coskun et al., 2022)

Forty-seven healthy volunteers received single doses. The study established the ~6-day half-life, dose-proportional pharmacokinetics, and the 12–72 hour Tmax window.

Phase 1b Multiple-Ascending-Dose Study (Urva et al., Lancet 2022)

Adults with type 2 diabetes received weekly doses over 12 weeks at 0.5 mg, 1.5 mg, 3 mg, 3/6 mg (escalating), and 3/6/9/12 mg (escalating), with placebo and dulaglutide 1.5 mg as comparators.

Key findings:

Pharmacokinetics were dose proportional
Steady-state exposures were maintained with once-weekly dosing
Body weight reduction was dose-dependent: up to -8.96 kg in the highest dose group vs placebo at 12 weeks
HbA1c reductions of -0.4% to -1.2% across dose groups
Safety profile consistent with other incretin drugs (GI adverse events most common)

Drug Interactions and Kidney Function: What Has Been Studied

Retatrutide is cleared by proteolytic degradation rather than through the cytochrome P450 system. Three completed Lilly trials sit next to that fact, and they ask three different questions: whether retatrutide changes the exposure of an oral drug taken alongside it; whether impaired kidneys change retatrutide's own exposure; and what retatrutide does to kidney function in people who already have chronic kidney disease. All three are marked completed. None has posted results to ClinicalTrials.gov as of July 2026.

Study	Phase	Participants	What it measures	Registry status
NCT06808802	Phase 1	30 healthy adults (BMI 22.0–35.0)	Whether retatrutide changes the AUC and Cmax of oral metoprolol	Completed April 15, 2025 — no results posted
NCT05611957	Phase 1	29 adults across three arms — normal renal function, severe renal impairment, end-stage renal disease	Retatrutide's own AUC and Cmax in impaired kidneys versus normal	Completed September 5, 2023 — no results posted
NCT05936151	Phase 2b	146 adults (BMI 27 or above, chronic kidney disease, with or without type 2 diabetes)	The effect of retatrutide on kidney function — change from baseline in measured glomerular filtration rate (mGFR) at week 24	Primary completion October 1, 2025 — no results posted

The metoprolol interaction study

Study J1I-MC-GZQE (NCT06808802) is an open-label, single-arm, within-participant comparison. Participants took a single oral dose of metoprolol, waited a one-week washout, then received subcutaneous retatrutide followed by a second oral dose of metoprolol. Metoprolol exposure — area under the concentration curve from time zero to infinity, and maximum concentration — was measured across days 1–3 and again across days 9–11, so the two readings differ only by whether retatrutide was on board. Thirty overtly healthy adults enrolled; the trial completed on April 15, 2025.

The renal-impairment PK study

NCT05611957 is the study that speaks directly to this page's subject. It is a parallel-group, open-label Phase 1 trial in 29 adults split across three arms — normal renal function (eGFR of 90 mL/min or above), severe renal impairment, and end-stage renal disease — all given subcutaneous retatrutide. The primary endpoints are retatrutide's own AUC from time zero to infinity and its maximum observed concentration, sampled from predose out to 31 days. It completed on September 5, 2023, and the registry record has carried no results since.

That is the trial that would tell you whether reduced kidney function raises retatrutide exposure. Because it has not reported, the answer is unpublished — not reassuring, not alarming, simply unknown.

The kidney-function study

NCT05936151 asks the opposite question. It is a Phase 2b, double-blind, placebo-controlled trial in 146 adults with a BMI of 27 or above and chronic kidney disease, with or without type 2 diabetes. It ran about 31 weeks, with change from baseline in measured glomerular filtration rate at week 24 as the primary endpoint — what retatrutide does to the kidneys, not what impaired kidneys do to retatrutide. It has no plasma pharmacokinetic endpoints. Primary completion was October 1, 2025; the registry records study completion on October 21, 2025.

What is not known yet

All three records show no posted results, so the actual numbers — whether metoprolol exposure shifted, how retatrutide exposure differed in end-stage renal disease, and what happened to measured GFR — are not public. Until they are, this page states only what was measured and in whom. If you take other medications or have kidney disease, that is a conversation for the clinician managing it, not something to infer from a trial design.

Frequently Asked Questions

How long does retatrutide stay in your system?

With a half-life of ~6 days, retatrutide is essentially eliminated after about 30 days (5 half-lives) following the last dose. However, some trace amounts may be detectable longer depending on cumulative exposure.

Why is the half-life important?

The 6-day half-life means drug levels remain relatively stable throughout the week, providing consistent appetite suppression and metabolic effects without daily dosing. It also means side effects, if they occur, may persist for several days after a dose.

Can I take retatrutide every two weeks instead of weekly?

This has not been studied in clinical trials. The once-weekly dosing was specifically calibrated to maintain therapeutic drug levels based on the 6-day half-life. Less frequent dosing would result in lower trough concentrations and reduced efficacy.

How does the half-life compare to other GLP-1 drugs?

Retatrutide's 6-day half-life is slightly shorter than semaglutide (~7 days) and slightly longer than tirzepatide (~5 days). All three support once-weekly dosing. The differences are clinically insignificant.

Does retatrutide interact with other medications?

Retatrutide does not interact with cytochrome P450 enzymes, so the drug-drug interactions that route through that pathway do not apply. Lilly nevertheless ran a dedicated Phase 1 study — NCT06808802, 30 healthy adults, completed April 15, 2025 — to measure whether retatrutide changes the exposure of oral metoprolol. No results have been posted to the registry, so the answer for oral drugs taken alongside retatrutide is not yet public. Anyone on other prescriptions should raise it with the clinician managing them.

Does impaired kidney function change retatrutide's half-life or exposure?

There is a completed trial designed to answer exactly that, and it has not reported. NCT05611957 is a Phase 1, open-label, parallel-group study in 29 adults with normal renal function, severe renal impairment, or end-stage renal disease, measuring retatrutide's AUC and Cmax in each group. It completed on September 5, 2023 and has posted no results. So the honest answer is that the comparison exists but the numbers are not public.

A separate Phase 2b trial, NCT05936151 in 146 adults with chronic kidney disease, asks the reverse question — what retatrutide does to kidney function, measured as change in glomerular filtration rate at week 24. It has also posted no results. Neither trial is a substitute for a clinician who knows your kidney function.

Sources

Coskun, T., et al. (2022). LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist for glycemic control and weight loss. Cell Metabolism. DOI: 10.1016/j.cmet.2022.07.013.
Urva, S., et al. (2022). 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. The Lancet. DOI: 10.1016/S0140-6736(22)02033-5.
Min, T., et al. (2025). A comprehensive review on the pharmacokinetics and drug-drug interactions of GLP-1 receptor agonists. Drug Design, Development and Therapy. DovePress.
ClinicalTrials.gov. NCT06808802 — A Phase 1, Open-label, Single-arm Study to Investigate the Effect of Retatrutide on Metoprolol Pharmacokinetics in Healthy Participants (J1I-MC-GZQE). Completed; 30 participants; record last updated June 5, 2025.
ClinicalTrials.gov. NCT05611957 — A Parallel-group, Phase 1, Open-label Study to Investigate the Pharmacokinetics of LY3437943 in Participants With Renal Impairment Compared With Healthy Participants. Completed September 5, 2023; 29 participants; record last updated October 2, 2023.
ClinicalTrials.gov. NCT05936151 — A Phase 2b, Double-Blind Study to Investigate the Effect of Retatrutide on Renal Function in Participants With Overweight or Obesity and Chronic Kidney Disease With or Without Type 2 Diabetes. Primary completion October 1, 2025; 146 participants; record last updated November 25, 2025.

Questions to ask your doctor

Given my health history, is a GLP-1 medication appropriate for me at all?
Which approved option (e.g. semaglutide, tirzepatide) best fits my goals?
What starting dose and titration pace would you use, and why?
What side effects should I watch for, and when should I call you?
How will we monitor whether it's working and when to adjust?

How we keep this honest

What this is: Educational information, not medical advice. It reports published research — it doesn’t recommend that you use, obtain, or supply anything.
Regulatory status: Retatrutide and similar peptides are investigational — not approved by the FDA or any regulator. Semaglutide and tirzepatide are prescription-only medicines, available only through a licensed prescriber.
Our standard: Every claim traces to a primary source. We label the strength of evidence and flag estimates as estimates — never as clinical fact.
No commercial ties: We don’t sell, supply, or link to suppliers of any medicine, and aren’t affiliated with any manufacturer.

Do not make decisions about your health without consulting a qualified healthcare provider. For trial enrolment, see ClinicalTrials.gov. More on how we review.

Sources