The Incretin Peptide Generations
The past decade has seen a rapid evolution in incretin-based peptide research, progressing from single-receptor agonists to multi-receptor compounds with increasingly potent metabolic effects:
- First generation — GLP-1 monotherapy (e.g. Semaglutide): proven cardiovascular and metabolic safety profile, robust evidence base from large-scale trials
- Second generation — GLP-1/GIP dual agonism (e.g. Tirzepatide): enhanced weight reduction outcomes; GIP co-activation appears to improve tolerability and metabolic synergy
- Third generation — GLP-1/GIP/Glucagon triple agonism (e.g. Retatrutide): early-phase research showing potential for superior weight outcomes; glucagon receptor activity adds thermogenic and hepatic effects
Each generation builds on the preceding receptor targets rather than replacing them. Researchers selecting a compound should consider the specific pathways under investigation and the maturity of the clinical evidence base.
Receptor Target Comparison
| Compound | GLP-1R | GIPR | Glucagon R | Class |
|---|---|---|---|---|
| Semaglutide | ✓ | — | — | GLP-1 mono-agonist |
| Tirzepatide | ✓ | ✓ | — | Dual agonist |
| Retatrutide | ✓ | ✓ | ✓ | Triple agonist |
Clinical Weight Reduction Outcomes
Clinical trial data for each compound at the highest studied doses (approximate figures from peer-reviewed publications):
| Compound | Trial | Duration | Mean Weight Reduction |
|---|---|---|---|
| Semaglutide 2.4mg | STEP 1 | 68 weeks | ~14.9% |
| Tirzepatide 15mg | SURMOUNT-1 | 72 weeks | ~20.9% |
| Retatrutide 12mg | Phase 2 (NEJM 2023) | 48 weeks | ~24.2% |
Researchers should note that direct head-to-head comparisons across these compounds are limited; trial populations, durations, and endpoints differ. Phase 3 data for Retatrutide is ongoing as of 2026. For a detailed review of the clinical evidence behind these weight outcomes, see GLP-1 Peptides and Weight Loss: What the Clinical Evidence Shows.
Which Compound for Your Research?
Selecting the appropriate compound depends on the specific receptor pathway under investigation:
- Semaglutide — ideal for GLP-1 receptor-specific studies, cardiovascular research, or protocols requiring an extensive published evidence base. Largest body of clinical literature.
- Tirzepatide — suited for dual incretin research, comparison studies against GLP-1 monotherapy, or investigations into GIP receptor contributions to metabolic regulation.
- Retatrutide — appropriate for triple-agonist mechanistic studies, thermogenesis and energy expenditure research, or investigations into glucagon receptor contributions beyond GLP-1/GIP signalling. Phase 2 data available; Phase 3 ongoing.