Retatrutide vs Tirzepatide vs Mounjaro® — Which Is Best for Weight Loss? (2025)
Posted on March 12, 2025 by admin
Retatrutide vs Tirzepatide vs Mounjaro® — Full 2025 Comparison
With multiple powerful GLP-1 options available in the UK — retatrutide, tirzepatide, and brand-name Mounjaro® — choosing the right compound can be confusing. This guide provides a direct, evidence-based comparison to help you decide.
The Key Difference — Mechanism of Action
| Compound | Mechanism | Receptors |
|---|---|---|
| Retatrutide | Triple agonist | GLP-1 + GIP + GCG |
| Tirzepatide / Mounjaro® | Dual agonist | GLP-1 + GIP |
| Semaglutide / Ozempic® | Single agonist | GLP-1 only |
The addition of glucagon (GCG) receptor activation in retatrutide is the critical difference — it adds a third fat-burning mechanism that increases resting energy expenditure, a mechanism absent from tirzepatide and semaglutide.
Weight Loss Results — Head-to-Head Comparison
| Compound | Average Weight Loss | % Losing ≥20% | Trial Duration |
|---|---|---|---|
| Retatrutide 24mg | 24.2% | 83% | 48 weeks |
| Tirzepatide 15mg (Mounjaro®) | 22.5% | 56% | 72 weeks |
| Semaglutide 2.4mg (Ozempic®/Wegovy®) | 14.9% | 32% | 68 weeks |
Sources: Retatrutide NEJM 2023 · Tirzepatide NEJM 2022 · Semaglutide NEJM 2021
Retatrutide vs Tirzepatide — The Practical Differences
- Weight loss: Retatrutide produces meaningfully greater average weight loss (24.2% vs 22.5%). The difference is more pronounced at the high end — 83% of retatrutide patients lost ≥20% body weight vs 56% for tirzepatide. For someone weighing 100kg, this is the difference between losing ~22kg vs ~24kg — significant in absolute terms.
- Side effects: Both have very similar GI side effect profiles. Retatrutide uniquely produces a modest heart rate increase (4–6 bpm average) due to glucagon receptor activation — this is absent with tirzepatide. For most healthy adults, this is clinically insignificant, but relevant for those with cardiac concerns.
- Evidence base: Tirzepatide has a larger evidence base — Phase 3 SURMOUNT trials enrolled thousands of participants across multiple years. Retatrutide’s Phase 2 data is compelling but Phase 3 results are still emerging. Tirzepatide is the more established compound with more long-term safety data.
Price in UK (2025)
- Compounded retatrutide 40mg: £299/month
- Compounded tirzepatide 20mg: from £199/month
- Mounjaro® brand (Rx): £1,050–£1,400/month
Retatrutide vs Mounjaro® — Are They the Same?
No — they are different molecules entirely. Mounjaro® contains tirzepatide (dual GLP-1/GIP agonist). Retatrutide is a triple GLP-1/GIP/GCG agonist. There is no brand-name retatrutide currently available — it has not yet received MHRA or FDA approval. Retatrutide is available in the UK only as a compounded research peptide.
Which Should You Choose?
- Choose retatrutide if:
- You want maximum weight loss results
- You have tried semaglutide or tirzepatide with suboptimal results
- You are comfortable with the newer evidence base
- Your budget is £299/month or above
- Choose tirzepatide if:
- You want strong results with a better-established safety profile
- You prefer the dual agonist without glucagon effects
- Your budget is tighter — effective from £199/month
- You have any cardiac history (avoid glucagon component)