If you are trying to understand the new wave of metabolic peptides, these three names come up again and again. Semaglutide, Tirzepatide, and Retatrutide represent three generations of the same idea, and lining them up side by side reveals one of the clearest stories in modern medicine: with each generation, scientists added a target, and with each added target, the results grew. Here is how they actually compare.
The one-target, two-target, three-target story
The simplest way to understand these three is by counting the hormone systems each one activates.
Semaglutide is a single agonist. It mimics one gut hormone, GLP-1, which reduces appetite and slows the emptying of the stomach. It was the breakthrough that proved a peptide could drive serious weight loss.
Tirzepatide is a dual agonist. It activates GLP-1 and a second hormone, GIP, at the same time. Adding the second target produced noticeably stronger results than the single-target approach.
Retatrutide is a triple agonist. It activates GLP-1, GIP, and a third, glucagon, which adds an energy-expenditure and fat-burning dimension on top of appetite control. It is the newest and, in trials so far, the most powerful of the three.
What the trials showed
The weight-loss data follow the same upward progression as the number of targets, and the trials are large and rigorous.
Semaglutide, in the STEP 1 trial (published in the New England Journal of Medicine in 2021), produced roughly 15% average body-weight reduction at its 2.4 mg dose over 68 weeks.
Tirzepatide, in the SURMOUNT-1 trial (NEJM, 2022, over 2,500 participants), produced up to about 22.5% average weight reduction at its highest dose over 72 weeks, and analysis showed the loss came overwhelmingly from fat rather than lean mass.
Retatrutide, in its Phase 2 trial (Jastreboff et al., NEJM, 2023), produced about 24.2% average weight reduction at its highest dose over 48 weeks, the highest figure of the three and achieved in less time.
Side-by-side comparison
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Class | Single agonist | Dual agonist | Triple agonist |
| Targets | GLP-1 | GLP-1 + GIP | GLP-1 + GIP + glucagon |
| Key trial | STEP 1 (2021) | SURMOUNT-1 (2022) | Phase 2 (2023) |
| Avg weight loss | ~15% | ~22.5% | ~24.2% |
| Added dimension | Appetite | Appetite + insulin/fat | Appetite + energy burn |
| Generation | First | Second | Third (newest) |
How to think about the differences
The progression is not random. Semaglutide established that targeting GLP-1 works. Tirzepatide showed that adding GIP, which complements GLP-1’s effects on insulin and fat handling, pushes results higher. Retatrutide’s third target, glucagon, brings in increased energy expenditure, which is why it leads on the weight-loss numbers and does so over a shorter trial period. Each is a legitimate landmark; they simply sit at different points on the same upward curve.
For research purposes, that means the choice often comes down to which mechanism is being studied. Single-target work points to Semaglutide; the dual-incretin approach points to Tirzepatide; and the cutting edge of triple-agonist research points to Retatrutide.
The bottom line
Across these three, more targets have meant more weight loss: Semaglutide (~15%) opened the door, Tirzepatide (~22.5%) raised the bar with a second hormone, and Retatrutide (~24.2%) leads the field with a third. They represent three generations of the same powerful idea. For full detail on each, see their individual research guides.
References
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. STEP 1, New England Journal of Medicine, 2021;384:989.
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity. SURMOUNT-1, New England Journal of Medicine, 2022;387:205.
- Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity, a Phase 2 trial. New England Journal of Medicine, 2023;389:514.
For laboratory and research use only.