Comparison

Retatrutide vs Tirzepatide

The next-generation triple agonist vs the current dual-agonist leader. Retatrutide adds glucagon receptor activity on top of GLP-1/GIP — here is what that changes in the data and in the lab.

Retatrutide

Triple GLP-1 / GIP / Glucagon agonist. Highest weight-loss signal in trials to date.

Mechanism: GLP-1 + GIP + Glucagon
Half-life: ~6 days
Dosing cadence: Weekly
Phase 2 weight loss: ~24% at 48 weeks
Status: Investigational

Strengths

· Highest peak weight-loss reported in any GLP-1-class trial
· Glucagon arm increases resting energy expenditure
· Weekly cadence, familiar handling

Trade-offs

· Not yet approved — Phase 3 ongoing
· GI side effects meaningful at higher doses
· Long-term safety data still limited

Full Retatrutide guide

Tirzepatide

Dual GLP-1 / GIP agonist. Approved, established, still class-leading in clinic.

Mechanism: GLP-1 + GIP
Half-life: ~5 days
Dosing cadence: Weekly
SURMOUNT weight loss: ~21% at 72 weeks
Status: Approved (Mounjaro / Zepbound)

Strengths

· Full Phase 3 evidence base
· Approved indications for T2D and obesity
· Well-characterised handling and titration

Trade-offs

· Lower peak weight loss than retatrutide in cross-trial reads
· No glucagon arm — energy expenditure less pronounced

Full Tirzepatide guide

Which one wins?

On paper retatrutide is the more potent molecule — Phase 2 data suggests roughly 3 percentage points more weight loss than the best tirzepatide numbers. But retatrutide is still investigational; tirzepatide has years of real-world use and full outcome data behind it.

For research handling both behave the same: lyophilised powder, reconstitute with BAC water, refrigerate once mixed. What actually determines your outcome is the purity of the vial you receive — a 92% pure retatrutide will underperform a 99% pure tirzepatide every single time.

Mechanism: dual vs triple agonism

Tirzepatide activates two receptors (GLP-1, GIP). Retatrutide adds a third — the glucagon receptor — which increases hepatic energy expenditure and lipolysis. The three-way balance is what unlocks the higher weight-loss ceiling.

See our GLP-1 brand names map for how each molecule maps to its clinical name, and the compound background at PeptidesUK4U.

Dosing approach

Both are weekly subcutaneous. For retatrutide this library uses a low-and-slow schedule — 2 mg for weeks 1–4, 3 mg for weeks 5–6, 4 mg for weeks 7–8 — moving up 1 mg at a time only when there are no side effects and food suppression has faded, so the lowest working dose is held as long as possible. Use a reconstitution calculator to convert vial mg + BAC water mL into exact U-100 units.

Storage and handling

Lyophilised powder stable months at 2–8 °C. Reconstituted vials ~28 days refrigerated — see the storage & stability guide. Source only from suppliers who publish batch-specific HPLC CoAs.