Drug facts

Retatrutide vs tirzepatide

Reviewed August 2026

The difference that matters most

It is not the third receptor. It is that one of these has been through FDA review and the other has not been through it anywhere.

Tirzepatide is sold as Mounjaro and Zepbound, with a label that states what it is approved for, what it must warn about, and how it is made. Retatrutide has none of that yet. Its manufacturer is still running the trials that would produce it. That is not a criticism of the molecule — it is a description of how much is currently known about giving it to people outside a trial, which is: much less.

The rest of this site is about compounded tirzepatide, where the molecule itself is approved and the preparation is not reviewed. Retatrutide is a step further out than that, and the distinction is worth holding onto.

Two receptors against three³

Tirzepatide’s own label describes it as a GIP receptor and GLP-1 receptor agonist — two targets. Retatrutide is described in its published trials as an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and glucagon receptors. The glucagon arm is the new one, and it is the reason the drug is interesting: glucagon receptor activity is associated with energy expenditure rather than appetite alone.

A third target is not automatically a better drug. It is a different drug, with its own side-effect profile to establish — and establishing it is what the trials below are for.

What the retatrutide trials measured¹

The phase 2 obesity trial enrolled 338 adults and reported, at 48 weeks, a least-squares mean change in body weight of −8.7% at 1 mg, −17.1% in the combined 4 mg group, −22.8% in the combined 8 mg group and −24.2% at 12 mg, against −2.1% on placebo. At 24 weeks the same groups were at −7.2%, −12.9%, −17.3% and −17.5%, against −1.6% on placebo.

The trial also reported how many people crossed each threshold at 48 weeks: on 12 mg, 100% lost at least 5%, 93% at least 10% and 83% at least 15%, against 27%, 9% and 2% on placebo. The most common adverse events were gastrointestinal, dose-related and mostly mild to moderate, and dose-dependent increases in heart rate peaked at 24 weeks before declining.

²A phase 3 trial in type 2 diabetes has since reported. It randomised 537 adults whose diabetes was not controlled by diet and exercise alone, and at 40 weeks reported mean weight change of −11.5% at 4 mg, −13.9% at 9 mg and −15.3% at 12 mg against −2.6% on placebo, alongside HbA1c reductions of 1.69, 1.86 and 1.94 percentage points against 0.81 on placebo. Two deaths occurred during that study, both in the 4 mg group.

Why you cannot compare the two numbers

It is tempting to set retatrutide’s −24.2% beside a tirzepatide figure and call one bigger. That comparison is not available from these papers, and here is why.

The two drugs have not been tested against each other. Every figure above comes from a trial comparing retatrutide with placebo, in its own population, over its own duration, with its own entry criteria. The phase 2 obesity trial ran 48 weeks in adults with obesity; the phase 3 trial ran 40 weeks in adults with type 2 diabetes, who lose less weight on these drugs than people without it. Reading across trials is how a drug acquires a reputation it has not earned — the same error this site spends its time on in the tirzepatide against semaglutide comparison, where a head-to-head trial does exist and is still widely misquoted.

What can be said is narrower and more useful: retatrutide has produced large weight reductions against placebo in two randomised trials, one of them phase 3, and nobody has yet published a trial putting it against tirzepatide.

What is being sold online

Retatrutide is sold today by sellers who describe it as a research chemical, and by some who do not describe it that way at all. There is no approved product for them to be compounding from, no label to dispense against, and no established dose outside a trial protocol.

This site does not index those sellers and does not price them. It indexes compounded tirzepatide, where an approved product exists and a reader can at least be told exactly how their vial differs from it. That line is where our evidence runs out, and we would rather say so than extend the index over a molecule whose own trials are still reporting.

Nothing here is a dosing instruction or a recommendation. Whether any of these medicines is appropriate for you is a question for a prescriber who knows your history, and the doses above are quoted from trial protocols to describe what was measured.