Semaglutide vs Retatrutide vs Tirzepatide : scientific comparison of GLP-1 peptides
Three generations of incretin agonist peptides, three levels of efficacy, three differentiating mechanisms. This in-depth comparison analyzes the clinical and preclinical data of each molecule to guide the choice of research protocols.
The evolution of GLP-1 agonists: three generations in 10 years
The discovery that GLP-1 (Glucagon-Like Peptide-1) analogs could induce significant weight loss transformed obesity research. In less than ten years, three generations of molecules emerged with progressively higher levels of efficacy:
- Generation 1: Semaglutide — GLP-1 monoagonist (~15% weight loss)
- Generation 2: Tirzepatide — dual GLP-1/GIP agonist (~22% weight loss)
- Generation 3: Retatrutide — triple GLP-1/GIP/glucagon agonist (~24% in 48 weeks)
Binding profiles and receptor selectivity
| Receiver | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| GLP-1R | ++++ (high affinity) | +++ (high affinity) | ++++ (high affinity) |
| GIPR | - (none) | ++++ (high affinity) | +++ (moderate affinity) |
| GCGR (glucagon) | - (none) | - (none) | +++ (moderate affinity) |
| Half-life | ~7 days | ~5 days | ~6 days |
| Administration | Weekly | Weekly | Weekly |
Semaglutide in detail
Structure and mechanism
Semaglutide is a human GLP-1 analog (7-37) with an Ala→Aib substitution at position 8 (DPP-4 resistance) and a C18 diacid chain attached via a spacer to lysine 26. Its affinity for the GLP-1R receptor is comparable to native GLP-1.
Main mechanisms:
- Appetite reduction via the hypothalamus (GLP-1R pathway)
- Slowing of gastric emptying (prolonged satiety)
- Stimulation of glucose-dependent insulin secretion
- Inhibition of postprandial glucagon secretion
Key clinical data
| Study | Population | Duration | Weight loss |
|---|---|---|---|
| STEP-1 | Obesity without T2DM | 68 weeks | -15,2% |
| STEP-2 | Obesity + T2DM | 68 weeks | -9,6% |
| STEP-4 | Continuation after 20 weeks. | +48 weeks | -7.9% additional |
| SELECT | Obesity + high CV | ~3 years | -10.2% · -20% MACE |
Tirzepatide in detail
The dual action of GLP-1 + GIP
Tirzepatide is a 39-amino-acid peptide designed as a balanced GLP-1/GIP agonist with a dual-arm architecture that allows for the simultaneous activation of both receptors. Its design is based on the GIP sequence with modifications that confer GLP-1R activity.
The addition of GIPR to GLP-1R synergizes on:
- Insulin sensitivity in adipose and muscle tissue
- The reduction of postprandial glucagon levels
- Improvement in pancreatic beta cell function
- The reduction of de novo lipogenesis in adipocytes
Key clinical data
| Study | Population | Duration | Weight loss |
|---|---|---|---|
| SURMOUNT-1 | Obesity without T2DM (5 mg) | 72 weeks | -15,0% |
| SURMOUNT-1 | Obesity without T2DM (10 mg) | 72 weeks | -19,5% |
| SURMOUNT-1 | Obesity without T2DM (15 mg) | 72 weeks | -22,5% |
| SURPASS-2 | T2DM vs Semaglutide | 40 weeks | Superior Tirze all doses |
Retatrutide in detail
The triple action: glucagon as the key differentiator
Retatrutide relies on a delicate balance of three agonist activities. The glucagon component is designed to be strong enough to activate thermogenesis and hepatic lipolysis, but sufficiently balanced by the actions of GLP-1 and GIP to avoid glucagon-induced hyperglycemia.
The unique effects provided by the GCGR component:
- Increase in basal energy expenditure (+5-8% in studies) — absent from Semaglutide and Tirzepatide
- Direct liver lipolysis → reduction of hepatic steatosis (-82% vs -34% placebo)
- Promoting mild ketogenesis (using fatty acids as a substrate)
- Additional therapeutic potential in NAFLD/NASH
Semaglutide and Tirzepatide reduce weight primarily by decreasing calorie intake (less appetite). Retatrutide adds an increase in energy expenditure via GCGR activation—meaning it "burns" more calories in addition to reducing food intake. This dual action on energy balance (intake AND output) is theoretically more robust in the long term.
Comparison of body compositions
Beyond the total weight, the body composition (Fat mass/lean mass ratio) is a more relevant indicator. The available data suggest:
| Setting | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Total fat mass loss | High | Very high | Very high |
| Loss of lean mass (muscle) | ~30-35% of the weight lost | ~25-30% | ~25% (estimated) |
| Visceral fat reduction | High | Very high | Very high |
| Liver fat reduction | Moderate (~40%) | High (~55%) | Very high (~82%) |
| Basal energy expenditure | Slightly modified | Slightly modified | Increased (+5-8%) |
Comparative tolerance profile
All three molecules share a GLP-1 class side effect profile dominated by gastrointestinal symptoms:
| Side effect | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Nausea | 40-50% | 35-45% | 40-60% |
| Vomiting | 15-25% | 10-20% | 15-30% |
| Diarrhea | 20-30% | 20-30% | 20-35% |
| Tachycardia | Lightweight | Lightweight | Moderate (GCG) |
| Stop for EI | ~5% | ~4% | ~7% (maximum dose) |
Which molecule for which research protocol?
Semaglutide — For:
- Reference study (established gold standard)
- Cardiovascular models (SELECT data)
- Pure GLP-1 effects, without GIP or glucagon
- Protocols requiring the best clinical documentation
- Comparisons with a well-established baseline
Tirzepatide — For:
- Study of the synergy of GLP-1/GIP
- Models of type 2 diabetes (SURPASS data)
- Body composition and insulin sensitivity
- Active vs. active comparisons (Tirze vs. Sema)
Study of the triple incretin action, exploration of glucagon mechanisms in obesity, research on NAFLD/NASH, energy expenditure models, next-generation comparative studies, effects on body composition (visceral/hepatic fat). The most relevant molecule for cutting-edge research.
The three peptides available at MyPeptide
Semaglutide, Tirzepatide, and Retatrutide are available for research at MyPeptide, HPLC certified 99%+, with Janoshik COA. EU shipping 48-72h.
Sources: Jastreboff 2023 NEJM (Retatrutide) · Wilding 2021 NEJM (Semaglutide) · Jastreboff 2022 NEJM (Tirzepatide)
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Scientific sources
To compare with other GLP-1 molecules, see our comparison Retatrutide vs Tirzepatide vs Semaglutide.