What actually separates the three?
All three are synthetic peptides that bind incretin receptors — the signalling system regulating insulin release, gastric emptying and satiety. What differs is how many of those receptors each one engages, and that single variable explains most of what follows.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Class | Single agonist | Dual agonist | Triple agonist |
| GLP-1 receptor | Yes | Yes | Yes |
| GIP receptor | No | Yes | Yes |
| Glucagon receptor | No | No | Yes |
| Developer | Novo Nordisk | Eli Lilly | Eli Lilly |
| Status | Approved | Approved | Investigational |
| Cardiovascular outcome data | Yes (SELECT) | Not published | Not published |
GLP-1 agonism is the shared foundation. GIP agonism, which tirzepatide adds, engages a second incretin pathway. Glucagon receptor agonism, which only retatrutide adds, is associated in published research with increased energy expenditure and reduced hepatic fat — a mechanism the other two do not touch at all.
What does the only head-to-head trial show?
SURMOUNT-5 is the one place where two of these compounds were put on the same footing. It randomised 751 adults with obesity and without diabetes, 1:1, to tirzepatide or semaglutide at maximum tolerated doses for 72 weeks. Because both arms ran in the same trial, under the same protocol, with the same population, the difference between them means something that cross-trial percentages do not.
| Measure | Tirzepatide | Semaglutide |
|---|---|---|
| Mean body-weight change | −20.2% | −13.7% |
| Mean waist circumference change | −18.4 cm | −13.0 cm |
| Achieved ≥30% weight reduction | 19.7% | 6.9% |
The proportion reaching at least 30% reduction is the most striking line — roughly a threefold difference. Note the trial was open-label rather than blinded, which is a real limitation when outcomes include behaviour, though body weight is among the more objective endpoints available.
Where does retatrutide sit?
Outside the comparison, strictly speaking. Retatrutide has never been trialled against tirzepatide or semaglutide, so there is no equivalent of SURMOUNT-5 for it.
What exists is its own pivotal trial. TRIUMPH-1 randomised 2,339 participants over 80 weeks and reported mean weight change of −17.6% at 4 mg, −23.7% at 9 mg and −25.0% at 12 mg, against −3.9% on placebo.
| Compound | Trial | n | Duration | Mean weight change |
|---|---|---|---|---|
| Semaglutide | STEP-1 (2021) | 1,961 | 68 weeks | −14.9% (2.4 mg) |
| Tirzepatide | SURMOUNT-1 (2022) | 2,539 | 72 weeks | −20.9% (15 mg) |
| Retatrutide | TRIUMPH-1 (2026) | 2,339 | 80 weeks | −25.0% (12 mg) |
Two of these three have been compared. The third has been measured, which is not the same thing.
The distinction that matters
Why semaglutide still matters despite the smallest numbers
On weight change semaglutide places last of the three. On evidence of clinical outcomes it is the only one with anything published at all.
The SELECT trial enrolled 17,604 participants aged 45 and over with established cardiovascular disease, overweight or obesity, and no diabetes, across 41 countries. It reported a 20% reduction in major adverse cardiovascular events — a composite of cardiovascular death, non-fatal myocardial infarction and non-fatal stroke — against placebo.
That is a different class of evidence from a weight-change percentage. Weight is a surrogate measure; cardiovascular events are an outcome. Neither tirzepatide nor retatrutide has published equivalent outcome data, which does not mean they lack the effect — only that it has not been demonstrated.
How do they differ in approval and availability?
- Semaglutide — approved in multiple markets for type 2 diabetes and for weight management, with the longest post-approval record of the three.
- Tirzepatide — approved in multiple markets, more recently, for both indications.
- Retatrutide — investigational. Not approved by any regulator, in clinical development by Eli Lilly.
That difference in status is also a difference in how much is known. An approved compound has accumulated post-marketing surveillance across far more people than any trial enrols; an investigational one has only its trial record, however large.
Do they differ in laboratory handling?
Very little. All three arrive as lyophilised powder and share the handling profile of the wider incretin class: refrigerated and light-protected as powder, reconstituted with bacteriostatic water added down the vial wall, swirled rather than shaken, and stable for substantially less time once in solution.
The reconstitution guide covers the full procedure and the concentration arithmetic, and the shipping guide covers what heat and humidity do to sealed vials in Indian transit — which matters more than the compound identity does.