Evidence review
'Best peptides for weight loss': what the research actually says
Search results on this topic are full of claims; the published record is narrower and more interesting. This guide reviews the actual trial data behind the incretin class — semaglutide, tirzepatide, retatrutide — and is clear about what remains unproven. A research overview, not medical advice.
The evidence belongs to one class
Strip away the marketing and the weight-management evidence base consists almost entirely of incretin-class compounds — peptides targeting the GLP-1, GIP and glucagon receptors. Each additional receptor has, so far, come with larger published effects:
| Compound | Receptors | Best published result | Status |
|---|---|---|---|
| Semaglutide | GLP-1 | −14.9% at 68 weeks (STEP 1) | Licensed (Wegovy) |
| Tirzepatide | GLP-1 + GIP | −20.9% at 72 weeks (SURMOUNT-1) | Licensed (Mounjaro) |
| Retatrutide | GLP-1 + GIP + glucagon | −24.2% at 48 weeks (Phase 2) | Phase 3 trials |
What the mechanisms research shows
The published mechanism work explains the progression. GLP-1 agonism slows gastric emptying and acts on hypothalamic appetite centres. GIP co-agonism appears to amplify the GLP-1 effect while improving tolerability. The glucagon receptor — retatrutide’s addition — shifts the equation from purely reduced intake to increased energy expenditure, which may explain why its weight-loss curve had not plateaued when its Phase 2 trial ended.
Equally important is what the research does not show: no published evidence supports weight-loss claims for repair peptides (BPC-157, TB-500), skin peptides (GHK-Cu), or most other compounds marketed alongside the incretin class. A claim without a trial behind it is marketing.
Incretin-class research compounds
Research-grade retatrutide and tirzepatide for laboratory use — third-party tested batch by batch, certificates of analysis available.
Frequently asked questions
Which peptide showed the most weight loss in trials?
Which peptide showed the most weight loss in trials?
How do incretin peptides cause weight loss in studies?
How do incretin peptides cause weight loss in studies?
Are weight-loss peptides available in the UK?
Are weight-loss peptides available in the UK?
Do peptides like BPC-157 cause weight loss?
Do peptides like BPC-157 cause weight loss?
Related reading
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