Comparison Guide
Retatrutide vs Tirzepatide (Mounjaro)the next generation, compared.
Retatrutide adds a third receptor — glucagon — to the GLP-1/GIP dual action of Tirzepatide. In separate trials, Retatrutide reached ≈24% mean weight loss at 48 weeks versus −20.9% for Tirzepatide at 72 weeks. Retatrutide is investigational and research-use-only; Tirzepatide is MHRA-approved.
This page focuses on the third receptor: how Retatrutide (LY3437943, triple agonist) extends the dual-agonist Mounjaro mechanism with glucagon activity, and what that adds — and costs — over Tirzepatide on potency, hepatic fat and tolerability.
At a glance
Retatrutide vs Tirzepatide: key differences.
Receptor targets
Retatrutide
GLP-1 + GIP + Glucagon (triple)
Tirzepatide
GLP-1 + GIP (dual)
Peak weight loss (Phase 2/3)
Retatrutide
≈24.2% at 48 wks · 12mg
Tirzepatide
≈20.9% at 72 wks · 15mg
Regulatory status (UK)
Retatrutide
Investigational — research only
Tirzepatide
MHRA approved (Mounjaro)
Full comparison
Retatrutide vs Tirzepatide: full spec sheet.
| Attribute | Retatrutide | Tirzepatide |
|---|---|---|
| Drug class | GLP-1/GIP/Glucagon triple agonist | GLP-1/GIP dual agonist |
| Developer | Eli Lilly (LY3437943) | Eli Lilly (LY3298176) |
| UK brand | None — investigational | Mounjaro |
| Administration | Weekly subcutaneous pen | Weekly subcutaneous pen |
| Max studied dose | 12 mg weekly | 15 mg weekly |
| Weight loss (peak) | ≈24% (Phase 2, 48 wks) | −20.9% (SURMOUNT-1, 72 wks) |
| HbA1c reduction | ≈2.0% at 12 mg | ≈2.1% at 15 mg |
| Hepatic fat reduction | Significant (glucagon arm) | Moderate |
| Common side effects | Nausea, GI, transient HR rise | Nausea, GI, decreased appetite |
| Phase 3 status | TRIUMPH program ongoing | Completed — approved |
Clinical evidence
Retatrutide vs Tirzepatide trial results (Phase 2 vs SURMOUNT-1).
Cross-trial comparisons aren't head-to-head, but the published Phase 2 Retatrutide data (Jastreboff et al., NEJM 2023) and the SURMOUNT-1 Tirzepatide trial (Jastreboff et al., NEJM 2022) give a directional read on relative potency.
Retatrutide · NEJM 2023
−24.2%
mean body weight at 48 weeks · 12mg dose
- • 100% of high-dose participants lost ≥5%
- • 83% lost ≥15%
- • 26% lost ≥30%
Tirzepatide · SURMOUNT-1
−20.9%
mean body weight at 72 weeks · 15mg dose
- • 96% lost ≥5%
- • 57% lost ≥20%
- • 36% lost ≥25%
Titration
Both titrate slowly. Retatrutide goes further.
Retatrutide titration
- Weeks 1–4: 2 mg weekly
- Weeks 5–8: 4 mg weekly
- Weeks 9–12: 6 mg weekly
- Weeks 13–16: 8 mg weekly
- Weeks 17+: 10–12 mg weekly
Tirzepatide titration
- Weeks 1–4: 2.5 mg weekly
- Weeks 5–8: 5 mg weekly
- Weeks 9–12: 7.5 mg weekly
- Weeks 13–16: 10 mg weekly
- Weeks 17+: 12.5–15 mg weekly
Tolerability
Side-effect profile.
Both molecules share the GLP-1-driven GI signature. Retatrutide's glucagon arm adds a transient heart-rate increase observed in trials. Slow titration significantly reduces dropout in both.
Nausea
Most common · diminishes after weeks 4–8 in both
Diarrhoea / constipation
Dose-dependent · pronounced in early titration
Decreased appetite
Expected pharmacological effect
Heart-rate (Retatrutide)
Modest transient increase reported in Phase 2
Injection-site reaction
Uncommon · usually self-limiting
Cautions & contraindications
Limitations & who this isn't for.
Retatrutide is an investigational triple agonist supplied for laboratory research only — it is not approved by the MHRA for human use, and nothing here is medical advice. The extra glucagon receptor that distinguishes it from Tirzepatide also carries the class cautions below.
Not for human use
Retatrutide is not MHRA-approved. Research-grade pens are supplied for in-vitro laboratory use only, not for self-administration or treatment.
Glucagon-driven heart-rate rise
Retatrutide's glucagon agonism — the receptor Tirzepatide lacks — produced a transient increase in heart rate in Phase 2. Relevant where cardiovascular parameters are a study variable.
Dose-dependent GI effects
Nausea, vomiting, diarrhoea and constipation rise with dose and rapid titration for the whole GLP-1/GIP/glucagon class. Both molecules share this signature.
No head-to-head data
All Retatrutide-vs-Tirzepatide figures here are cross-trial, not direct comparisons. Endpoints (48 vs 72 weeks) and populations differ.
Who it would be inappropriate for
In any clinical context, GLP-1-class agonists are generally avoided with a personal/family history of medullary thyroid carcinoma or MEN 2, pancreatitis, or during pregnancy — decisions that belong to a qualified clinician, not this page.
The verdict
Retatrutide leads on weight loss. Tirzepatide leads on approval.
Body Pharm Retatrutide pens are supplied in the UK for laboratory research — 32mg and 64mg multi-dose pens, cold-chain shipped, with batch COA on request.
Common Questions
Retatrutide vs Tirzepatide FAQ.
Is Retatrutide stronger than Tirzepatide?
Phase 2 Retatrutide data suggests greater mean weight reduction (≈24% at 48 weeks at 12mg) than the Tirzepatide SURMOUNT-1 outcome (−20.9% at 72 weeks at 15mg). These are cross-trial comparisons, not head-to-head; direct head-to-head trials have not yet reported.
Is Retatrutide MHRA approved in the UK?
No. Retatrutide is investigational. It is supplied in the UK for in-vitro research only. Tirzepatide (Mounjaro) is MHRA approved for type 2 diabetes and weight management.
Do they share side effects?
Yes — both produce the typical GLP-1 GI signature (nausea, altered bowel habit, reduced appetite). Retatrutide also shows a transient heart-rate increase from glucagon receptor activity.
Can I switch from Tirzepatide to Retatrutide?
In a clinical context, switching agonists should follow physician guidance. Research-grade Retatrutide pens supplied by Retatrutide UK are not intended for human use.