Retatrutide vs tirzepatide: two receptors against three, and how much evidence each one has
· Novatheris
The retatrutide vs tirzepatide question comes up in almost every metabolic research group. The short answer: they are similar in design, but they are not at the same point. One has years of large published trials. The other has promising results and a lot left to confirm.
Here we put them side by side, using the same sources we use in each product's fact sheet.
How they are alike
Both are a single peptide that activates several hormone receptors at once. Both use the GIP and GLP-1 receptors, two hormones the gut releases after a meal. And in all the trials cited here, both were studied by the subcutaneous route and as long-acting molecules.
They also share their size. Tirzepatide weighs 4813.53 Da and retatrutide 4730.477 Da. For a lab, that means they are analyzed with similar methods, and identity confirmation depends on measuring that weight correctly.
The core difference: two receptors against three
Tirzepatide is a dual agonist. It activates GIP and GLP-1.
Retatrutide is a triple agonist. It activates GIP, GLP-1 and also the receptor for glucagon, a hormone from the pancreas. According to the studies, that third arm adds increased energy expenditure to the effect the other two have on appetite.
That is the underlying reason they are studied separately. It is not the same molecule at another strength. It is a different way of acting on the system.
The chemistry, side by side
Tirzepatide. Formula C225 H348 N48 O68. Sequence based on GIP, with a 20-carbon fatty-acid chain that binds albumin. Half-life in humans of about 5 days, according to the drug's label. CAS 2023788-19-2.
Retatrutide. Molecular weight 4730.477 Da. We do not include a formula or sequence because we found no published source we can cite. There is no published numeric half-life: the phase 1 single-dose study showed a profile compatible with action lasting several days, and body weight was still reduced on day 43 after a single dose (Coskun et al., Cell Metab 2022). CAS 2381089-83-2.
For both, the lyophilized (freeze-dried) powder is stored at -20 °C and the reconstituted solution at 2 to 8 °C, short term only.
How much evidence each one has
This is the difference that weighs the most.
Tirzepatide has several published phase 3 trials. SURMOUNT-1 followed 2539 adults with obesity or overweight for 72 weeks and measured mean weight change of -15.0 %, -19.5 % and -20.9 % depending on dose, versus -3.1 % with placebo (Jastreboff et al., N Engl J Med 2022). SURMOUNT-5 compared it head to head with semaglutide in 751 adults: -20.2 % versus -13.7 % (Aronne et al., N Engl J Med 2025). And there is a withdrawal trial, SURMOUNT-4, that measured what happens on discontinuation.
Retatrutide has a phase 2 obesity trial with 338 adults over 48 weeks. It measured mean weight change of -8.7 %, -17.1 %, -22.8 % and -24.2 % depending on dose, versus -2.1 % with placebo (Jastreboff et al., N Engl J Med 2023). Its only published phase 3 trial is in type 2 diabetes: TRANSCEND-T2D-1, with 537 adults over 40 weeks, measured -11.5 %, -13.9 % and -15.3 % versus -2.6 % with placebo (Bajaj et al., Lancet 2026).
In short: tirzepatide has thousands of phase 3 participants and 72-week follow-up. Retatrutide has hundreds in phase 2 for obesity and one phase 3 trial in diabetes.
Why loose figures do not compare
It is tempting to put -24.2 % next to -20.9 % and declare a winner. It does not work that way.
None of the studies cited in our fact sheets compares the two molecules with each other. The figures come from different trials, with different populations, different durations (48 versus 72 weeks) and different phases. A phase 2 trial with 338 people and a phase 3 trial with 2539 do not give the same kind of certainty.
Comparing numbers from different trials is like comparing times from two races run on different tracks. It gives you an idea, not a result.
What is unknown about each one
Tirzepatide. What happens on discontinuation is known: in SURMOUNT-4, those switched to placebo regained 14.0 % of body weight over 52 weeks (Aronne et al., JAMA 2024). What is missing is something else: the lean mass figure comes from only 160 participants, and none of the 35 studies in a 2026 review measured strength or physical function.
Retatrutide. More is missing. There are no phase 3 obesity results. There is no published cardiovascular outcomes trial, and in phase 2 heart rate rose with dose up to week 24. And there is no published data on what happens after stopping, because the trials end with treatment still ongoing.
One shared point that matters when buying
The same holds for both: a vial of white powder does not tell you what is inside. A 2026 Australian study measured three products sold as 10 mg retatrutide and found 5.13, 16.5 and 19.0 mg (Piatkowski et al., Drug Alcohol Rev 2026). The label did not predict the content.
That is why at Novatheris every batch goes to Janoshik or Freedom Diagnostics, with +99.5 % purity required and the report published. You can check the one for tirzepatide and the one for retatrutide.
For research
Both are research reagents. We do not give doses or directions for use, and outside a clinical protocol neither has an established dose.
If your project compares the two molecules, the tirzepatide page and the retatrutide page have the full fact sheets with every citation, each one next to its lab report.