Mechanism of action
Tirzepatide activates two receptors: GLP-1 and GIP — together they suppress appetite, improve insulin sensitivity, and slow gastric emptying. Retatrutide adds a third — glucagon — which increases energy expenditure. The triple-agonist mechanism is why retatrutide is showing higher trial weight-loss numbers.
Clinical trial weight-loss results
Tirzepatide SURMOUNT-1 trial: ~20.9% mean weight loss at 72 weeks (15 mg dose). Retatrutide Phase 2 trial: ~24.2% mean weight loss at 48 weeks (12 mg dose). Final retatrutide Phase 3 data is expected in 2026.
Availability today
Tirzepatide is FDA-approved and available branded (Mounjaro, Zepbound) and compounded through 503A/503B pharmacies on the FDA shortage list when permitted. Retatrutide is investigational — not approved or commercially available — and any 'retatrutide' sold outside a clinical trial is not legally prescribable.






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