Retatrutide vs Semaglutide: One Receptor or Three

Semaglutide activates one receptor and is an approved medicine; retatrutide activates three and is still in clinical trials. Every other difference between them follows from those two facts.

A direct comparison is coming. A phase 3 trial of retatrutide against semaglutide is under way, but it has not reported, so for now the honest answer to "which is better" is that nobody has published the measurement.

What each one is

• Semaglutide is an acylated analogue of human GLP-1. Fatty-acid acylation extends its half-life to about a week, which is what makes once-weekly injection possible; it is also available as a daily oral tablet (Rybelsus). See the semaglutide profile.

• Retatrutide (LY3437943) is a single fatty-acylated peptide from Eli Lilly that activates the GIP, GLP-1 and glucagon receptors, given once weekly in trials. See the retatrutide profile or the plain-language introduction.

Tirzepatide sits between them: one molecule, two receptors (GIP and GLP-1). Retatrutide adds glucagon on top of that.

One receptor versus three

Semaglutide's effects all run through the GLP-1 receptor. It enhances glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying and reduces appetite through central pathways. Its weight effect runs mainly through appetite and intake.

Retatrutide keeps that GLP-1 action and adds two more:

• GIP receptor activation, thought to act on adipose tissue metabolism and hindbrain signalling — the component tirzepatide adds over semaglutide.

• Glucagon receptor activation, which raises hepatic energy expenditure and promotes fat oxidation. This works on the output side of energy balance rather than intake.

The glucagon arm is the interesting contrast. Semaglutide suppresses glucagon secretion as part of its glucose-lowering effect; retatrutide deliberately activates the glucagon receptor. Glucagon raises blood glucose, so that activation carries hyperglycaemic potential, and balancing it with enough incretin activity is the central design problem of triple agonists. That retatrutide's type 2 diabetes trials measured glycated haemoglobin is partly a test of whether the balance holds.

The retatrutide vs tirzepatide comparison isolates the glucagon step; the tirzepatide vs semaglutide comparison isolates the GIP step.

Side by side

What the trials and labels cover

Semaglutide

Semaglutide's dosing comes from its FDA prescribing information, which differs by product and indication:

• Wegovy, weight reduction. Titrated over 16 weeks to a 2.4 mg once-weekly maintenance dose (1.7 mg as an alternative), with escalation to a maximum of 7.2 mg once weekly permitted in adults.

• Wegovy, cardiovascular risk reduction. 2.4 mg (recommended) or 1.7 mg once weekly in adults with established cardiovascular disease and obesity or overweight.

• Ozempic, type 2 diabetes. Maintenance doses of 0.5, 1 or 2 mg once weekly; the 0.25 mg starting dose is an escalation step, not a maintenance dose.

The pivotal obesity evidence includes STEP 1, a phase 3 double-blind trial in adults with a BMI of 30 or more, or 27 or more with a weight-related condition, without diabetes. Participants received 2.4 mg once weekly for 68 weeks, with percentage change in body weight as the outcome (Wilding 2021). Its pharmacokinetics have been systematically reviewed (Yang 2024), and specific safety questions, including pancreatitis (Masson 2024) and thyroid cancer risk (Feier 2024), have their own reviews. The semaglutide dosage chart lays out the label regimens.

Retatrutide

Retatrutide has no label, so every dose figure comes from a trial:

• Obesity, phase 2. 338 adults randomised to 1, 4, 8 or 12 mg once weekly or placebo for 48 weeks, measuring percentage change in body weight (Jastreboff 2023).

• Type 2 diabetes, phase 2. 281 adults over 36 weeks at 0.5, 4, 8 or 12 mg once weekly, in a placebo- and active-controlled trial conducted in the USA, measuring glycated haemoglobin (Rosenstock 2023).

• Liver fat. A phase 2 substudy measuring liver fat content in adults with obesity and metabolic dysfunction-associated steatotic liver disease over 48 weeks (Sanyal 2024).

• Phase 3. TRANSCEND-T2D-1, in type 2 diabetes inadequately controlled with diet and exercise, has been published (Bajaj 2026); other phase 3 trials are ongoing.

Doses were reached by stepwise escalation inside the protocol, typically from 2 mg upward every four weeks. The 12 mg arm is the highest dose studied, not a target, and gastrointestinal effects were dose-dependent across the range. The retatrutide dosage chart sets out each arm against its source.

The head-to-head that has not reported

NCT06260722 is a phase 3 trial comparing retatrutide with semaglutide in 1,250 adults with obesity, with body weight as the outcome. It is listed as active, not recruiting, and has no results posted.

Until it reports, any retatrutide-versus-semaglutide percentage is cross-trial arithmetic: STEP 1 ran for 68 weeks in adults without diabetes; retatrutide's phase 2 obesity trial ran for 48 weeks in a different population. The two numbers were never meant to share a table.

There is a precedent for how much a proper head-to-head matters. SURPASS-2 randomised 1,879 adults with type 2 diabetes on metformin to tirzepatide (5, 10 or 15 mg) or semaglutide 1 mg for 40 weeks, measuring glycated haemoglobin (Frías 2021). A randomised comparison of that kind is the evidence mechanism cannot replace.

What the evidence does not show

• Whether retatrutide beats semaglutide. The trial designed to answer that has not published.

• Long-term safety of retatrutide. Semaglutide is approved and has dedicated safety reviews; retatrutide's full phase 3 safety data have not been published.

• That indirect comparisons settle it. A Bayesian network meta-analysis has ranked GLP-1 receptor agonists, dual agonists and retatrutide for weight loss (Sinha 2025). That is a useful hypothesis, but it depends on trials with different populations and durations being comparable.

• Anything about research-market material. Every result above comes from a specific pharmaceutical product under trial or label conditions.

Side effects

Gastrointestinal effects dominate both. Semaglutide's reported effects include nausea, vomiting, diarrhoea, constipation, abdominal pain, decreased appetite and gastro-oesophageal reflux, with pancreatitis and diabetic retinopathy complications as rare events. Retatrutide's reported effects include nausea, diarrhoea, constipation and an increase in heart rate.

The detail is in the semaglutide side effects and retatrutide side effects guides.

The vial math

For research-purpose concentration arithmetic, the calculation depends on vial mass and water volume alone. These are the reconstitution examples from our profiles:

The same syringe mark means a different mass in each row, which is the point: units are volume, not dose. The semaglutide calculator and retatrutide calculator work through each vial, and the insulin syringe units converter explains the markings.

Frequently asked questions

What is the difference between retatrutide and semaglutide?

Semaglutide activates the GLP-1 receptor only. Retatrutide activates the GLP-1, GIP and glucagon receptors. Semaglutide is FDA-approved; retatrutide is investigational.

Is retatrutide stronger than semaglutide?

That has not been shown. The phase 3 head-to-head trial, NCT06260722, has not posted results, and comparing figures from separate trials is not a valid substitute.

Is there a trial comparing retatrutide and semaglutide?

Yes. NCT06260722 compares them in 1,250 adults with obesity. It is active but not recruiting, and no results have been posted.

Is retatrutide FDA-approved?

No. It is an investigational drug. Its phase 2 trials and one phase 3 trial have been published; further phase 3 trials are ongoing.

Are they allowed in sport?

Semaglutide is permitted by WADA and included in its monitoring programme. Retatrutide is prohibited under the S0 category.