Retatrutide and Cagrilintide: Blend, Stack and Head-to-Head

Retatrutide and cagrilintide have never been tested together in people. The "reta cagri blend" sold online, usually 12.5 mg of retatrutide and 2.5 mg of cagrilintide in one vial, pairs Eli Lilly's triple agonist with Novo Nordisk's long-acting amylin drug, and no trial has measured what that pair does to weight or side effects. The closest human evidence is CagriSema, which pairs cagrilintide with semaglutide instead.

The idea behind the stack makes sense on paper: the two drugs hit different receptors, so they don't double up the way retatrutide and tirzepatide together would. Paper is all there is, though. With no human data on the pair, everything below leans on each drug's own trials, as of October 2026.

What is a reta cagri blend?

It's two drugs in one vial. The most common version in online listings and community dosing guides holds 12.5 mg of retatrutide and 2.5 mg of cagrilintide. That's a 5 to 1 ratio by weight. Users shorten it to "reta cagri", "reta/cag" or "cagri reta".

The two halves come from rival companies. Retatrutide is Lilly's once-weekly injection that acts on the GIP, GLP-1 and glucagon receptors, and Lilly calls it an investigational molecule that "cannot be legally sold or marketed for human use." Cagrilintide is Novo Nordisk's long-acting copy of amylin, a hormone the pancreas releases that makes you feel full, according to its Phase 2 paper in The Lancet. Neither company has registered a trial of the two together.

Have retatrutide and cagrilintide been tested together?

Not in people. We searched ClinicalTrials.gov again on October 31, 2026. It lists 33 records with retatrutide as an intervention, and none of them includes cagrilintide or any other amylin drug.

The only published study of the pair we found appeared in Nature Metabolism in September 2026. It gave retatrutide and cagrilintide together every day to obese animals and found more weight loss than either drug alone at equal molar doses. That result hasn't been tested in people, and the animals were dosed daily, while people inject both drugs once a week.

Lilly has its own amylin drug, eloralintide, which its Phase 2 paper in The Lancet calls a selective amylin receptor agonist. Lilly's registered trials pair eloralintide with tirzepatide, including a Phase 1 study in 188 people (NCT06916065) that finished in January 2026. None pairs it with retatrutide.

How the two drugs differ

Retatrutide works on three receptors. Cagrilintide works on two others: the amylin receptor and the calcitonin receptor, as the Nature Metabolism authors describe it.

Different receptors don't mean different side effects. Both drugs cause nausea, and in cagrilintide's Phase 2 trial, 20% to 47% of people on it had nausea over 26 weeks, against 18% on placebo. Both also have half-lives close to a week (see retatrutide's half-life), so splitting the shots across different days doesn't keep them apart.

Is cagrilintide more effective than retatrutide?

No. On the numbers published so far, cagrilintide alone is the weaker drug by a wide margin. The best data come from REDEFINE 1, Novo Nordisk's 68-week Phase 3 trial in 3,417 adults, which tested cagrilintide alone, semaglutide alone and the two together.

Retatrutide's top dose, with no second drug, went further than any row in that table. Here's TRIUMPH-1, Lilly's 80-week trial in 2,339 adults, published in NEJM on September 29, 2026 (the chart shows Lilly's efficacy-estimand figures, as if everyone stayed on treatment):

These are separate trials with different people and lengths, so they can't settle the question the way a head-to-head would. When Novo did run one, REDEFINE 4 put CagriSema against tirzepatide 15 mg for 84 weeks: 23.0% against 25.5% if everyone stayed on treatment. CagriSema failed its goal of showing it was no worse than tirzepatide. Retatrutide's first head-to-head result came on October 28, 2026, in type 2 diabetes: TRANSCEND-T2D-2 gave -19.5% (9 mg) and -20.9% (12 mg) against -9.4% on Ozempic 2 mg at 80 weeks, efficacy estimand. Its head-to-head against tirzepatide, TRIUMPH-5, lists an estimated primary completion of November 2026; our retatrutide vs tirzepatide page tracks it.

Look at the last column of the REDEFINE 1 table again. On cagrilintide alone, 82.5% of people were on the top dose at 68 weeks. On the pair, only 57.3% were. The trial let people adjust their dose, and many on the combination stayed lower.

Our read: that 57.3% is the most useful number for anyone thinking about a reta cagri stack. Two appetite drugs together were harder to push to full dose than either one alone, and nobody knows how that plays out with retatrutide, which already caused more stopping for side effects at 12 mg (11.3%) than CagriSema did (6%).

What a fixed 5 to 1 blend does to your dose

A fixed ratio ties the two doses together. Every milligram of retatrutide you draw brings 0.2 mg of cagrilintide with it. We worked through the retatrutide steps Lilly used in its Phase 3 trials, where everyone started at 2 mg and stepped up every 4 weeks. This is arithmetic, not a dosing plan.

Two problems fall out of that table. First, the blend picks the cagrilintide schedule for you. In REDEFINE 1, every active group spent 16 weeks stepping up to its full dose; in a blend, cagrilintide climbs only when retatrutide does, on retatrutide's timetable. Second, if you get sick after a step, you can't tell which drug caused it, and you can't lower one without lowering the other. Our retatrutide dosage schedule lists the trial steps for retatrutide alone.

Side effects that add up

Each part has its own side-effect record, from its own trials. They're different trials with different people, so read the table as a rough guide to what each drug brings.

About 4 in 10 people (42.4%) on retatrutide 12 mg had nausea with no second drug at all. Nobody has counted what adding cagrilintide does to that. In REDEFINE 1, 55% of people on cagrilintide plus semaglutide had nausea.

Vomiting and diarrhea matter beyond comfort. The Zepbound label warns that they can dry you out badly enough to injure the kidneys, some cases needing dialysis. That's tirzepatide data, not retatrutide, but it's the same kind of risk. Our retatrutide side effects guide covers each one, and the nausea page covers what helps.

What's actually in a vial sold as reta/cag

Neither half of the blend is an approved medicine. Retatrutide has no approved version anywhere (see is retatrutide legal), and Lilly says it "cannot be legally sold or marketed for human use." Cagrilintide has no US approval; Novo filed CagriSema with the FDA in December 2025 and said in February 2026 that it expected a decision by late 2026. We found no decision as of October 31, 2026. The FDA's page on unapproved GLP-1 drugs, current as of October 1, 2026, is blunt: "Retatrutide and cagrilintide cannot be used in compounding under federal law."

So every blend vial comes from a seller outside either company. Regulators have already found problems with single-drug vials. In an alert published September 14, 2026, Australia's TGA said it tested a vial sold as retatrutide after a user needed hospital care for uncontrollable vomiting: it held no retatrutide at all, and undeclared semaglutide at about 8 times the level in approved products. Victoria's health department linked 6 cases of liver injury since January 2026 to products labelled retatrutide, possibly from a contaminant.

A blend doubles the checking. A test report has to show the amount of both drugs in that batch, not just a purity figure for one. If you're weighing listings of retatrutide for sale, look for a batch-specific report from an independent lab that gives the milligrams of both peptides and carries the same batch number as the vial. Our guide to retatrutide vendors covers the red flags.

Our read: if hunger is what's pushing you toward a blend, the first thing to raise with a doctor is where you are in the retatrutide escalation. TRIUMPH-1's 4 mg group lost 19.0% on retatrutide alone, with no second drug. Other pairings people ask about are covered in retatrutide and GHK-Cu and retatrutide and MOTS-c; for what retatrutide does alone, see its results.