Retatrutide + Cagrilintide: The Evidence Ladder

Cagrilintide vs Retatrutide: The Two Molecules

Retatrutide and cagrilintide come from rival companies and act on different receptor families. Retatrutide is a single molecule that activates three incretin-family receptors.^[3] Cagrilintide is a long-acting analogue of amylin, a hormone the body releases after eating, and it also acts on calcitonin receptors.^[7][8][1] Together they reach five receptors, which is why the rat paper calls the approach “five-receptor polypharmacology”.^[1]

In TRIUMPH-1, adults with obesity on the highest retatrutide dose lost 25.0% of body weight over 80 weeks, against 3.9% on placebo.^[3] In REDEFINE 1, cagrilintide alone produced 11.8% weight loss against 2.3% for placebo over 68 weeks if all participants adhered to treatment, and Novo moved it into its own Phase 3 programme, RENEW.^[7] For the full retatrutide record, see the retatrutide research profile.

Why Pair Amylin With an Incretin Drug?

Amylin analogues and incretin drugs reduce appetite through partly different pathways, so researchers expect their effects to add up. The authors of the REIMAGINE 2 trial describe cagrilintide and semaglutide as having “complementary effects on glycaemic control and bodyweight”.^[9]

CagriSema is the proof of concept in humans. It pairs cagrilintide with semaglutide, a GLP-1 drug, in one fixed-dose product.^[6] In REDEFINE 1, a 68-week Phase 3 trial in 3,417 adults without diabetes, CagriSema produced a mean 20.4% weight loss against 3.0% with placebo. Gastrointestinal side effects were common: 79.6% of the CagriSema group against 39.9% on placebo.^[10] In REIMAGINE 2, in people with type 2 diabetes, CagriSema lowered HbA1c by 1.91 points against 1.75 for semaglutide alone.^[9]

In September 2026 Novo reported two more Phase 3 toplines. In REIMAGINE 5 (type 2 diabetes, week 60), lower-dose CagriSema gave 12.4% weight loss against 9.1% for a low dose of tirzepatide; in REDEFINE 9 it gave 21.0% against 2.0% for placebo.^[6] For the head-to-head picture, see CagriSema vs tirzepatide.

Retatrutide plus cagrilintide applies the same idea to a stronger incretin partner. Whether that adds up in people the way it did in rats is the open question.

The 2026 Nature Metabolism Study

The study came from the University of Copenhagen and was published online on September 15, 2026.^[1] Its experiments used diet-induced obese male rats, plus lean male rats for taste-aversion tests. Each experiment lasted 13 to 16 days, and the drugs were given once daily, whereas both are developed as once-weekly medicines in humans.^[1][3]

The combination cut body weight and food intake in a dose-dependent way, more than equimolar doses of either drug alone and more than matched cagrilintide pairings with semaglutide or tirzepatide. It also improved cholesterol, triglycerides and insulin. Pair-feeding and weight-matching showed that the extra weight loss “cannot be explained by reduced food intake alone”.^[1] In the brain, the combination produced stronger gene-module responses in the hypothalamus and the dorsal vagal complex than either drug alone.^[1]

Funding came from the Novo Nordisk Foundation, the Lundbeck Foundation and the Swedish Research Council, and the paper acknowledges platforms at the Novo Nordisk Foundation Center for Basic Metabolic Research. Several authors co-founded obesity-drug start-ups, one has received speaking fees from Novo Nordisk, one reports household holdings of Novo Nordisk stock, and one has received research support from Novo Nordisk and consulting fees from Eli Lilly and Zealand Pharma.^[1] The authors present the work as guidance for designing future single-molecule drugs that hit several receptors at once, not as a case for mixing two products.^[1]

The Evidence Ladder

Evidence for the pair sits on the lowest rung. The ladder below runs from rat data to human trials, and the top rung is empty.

ClinicalTrials.gov lists 33 studies of retatrutide and none that also includes cagrilintide.^[2] CagriSema shows that an amylin analogue can add to a GLP-1 drug in people.^[10] It does not show that cagrilintide adds safely to retatrutide, which also hits the glucagon receptor.^[3] For Novo’s other amylin projects, see amycretin and zenagamtide, and for a competitor, petrelintide.

Fixed-Ratio Blend vs Separate Vials

A fixed-ratio blend holds both peptides in one solution at a set mass ratio, so the proportion of one to the other cannot change. Separate vials keep each compound on its own, so each can be identified, tested and stored by itself. Both approaches exist on the research market. For how pre-mixed pens and lyophilized vials differ on stability and heat, see peptide pen vs vial.

We found no published stability or compatibility data for retatrutide and cagrilintide stored together in one solution. The sponsors have co-formulated other pairs: CagriSema is a fixed-dose combination, and Lilly plans to start Phase 3 trials of an eloralintide-tirzepatide co-formulation by the end of 2026.^[6][8] Those programmes generate their own stability data. Their results do not transfer to a different pair of peptides.

A certificate that reports one purity figure for a two-peptide blend does not show that both components are present in the stated amounts. Our COA and HPLC purity guide explains how to read peaks and mass data. To check a two-component report against the laboratory’s own record, see how to verify a Janoshik COA.

Cagrilintide vs Eloralintide

Eloralintide is Lilly’s own amylin drug, and it is often confused with cagrilintide. Lilly calls it a “selective amylin receptor agonist” and designed its combination with tirzepatide to act on GIP, GLP-1 and amylin receptors “with minimal activity at the calcitonin receptor”.^[8] Cagrilintide, by contrast, acts on both amylin and calcitonin receptors.^[1]

On September 30, 2026, Lilly reported a 48-week Phase 2b trial of eloralintide plus tirzepatide (EloraTZP) in 367 adults with obesity or overweight and type 2 diabetes. The highest-dose combination produced 23.3% weight loss against 14.8% for the highest tirzepatide dose alone, 12.3% at most for eloralintide alone and 3.0% for placebo. Discontinuation for side effects ranged from 10.8% to 27.0% with the combination.^[8] In that trial the two drugs were given separately. Eloralintide alone is already in Phase 3 for obesity.^[8]

Is “GLP-5” Real?

No. GLP-1 and GLP-2 are real hormones, both cut from the same precursor, proglucagon, along with glucagon and oxyntomodulin.^[11] There is no GLP-3, GLP-4 or GLP-5 hormone and no receptor by those names. Online, “GLP-3” is slang for retatrutide, and “GLP-5” has been used for retatrutide plus cagrilintide because the pair reaches five receptors: GLP-1, GIP, glucagon, amylin and calcitonin.^[1] The numbers count targets, not hormones, and the label says nothing about evidence or safety. For what “GLP-3” means and the seller codes built on it, see the GLP-3 retatrutide naming guide.

Regulatory Status

• Retatrutide. Investigational. Lilly plans to submit it to FDA in Q1 2027.^[4]
• Cagrilintide alone. In Phase 3 for obesity; not approved.^[5]
• CagriSema. Novo filed with FDA in December 2025 and expects a decision in Q4 2026; it “remains investigational”, and we found no public PDUFA date as of October 10, 2026.^[6] See Is CagriSema approved?
• Retatrutide plus cagrilintide. No sponsor programme, no registered human trial and no approval.^[2]

What This Page Does Not Cover

This page summarises published research and registry records. It does not cover dosing, preparation or use of any product, and it makes no therapeutic, human-use or veterinary claim. Rat results do not predict human outcomes.