Tirzepatide vs Retatrutide: Which Is Right for You?
Tirzepatide is FDA-approved (Zepbound, Mounjaro); retatrutide is investigational, not approved, and Lilly plans to file for approval in Q1 2027. Retatrutide adds glucagon-receptor activity and produced up to 22.6% mean weight loss at 80 weeks in TRIUMPH-3.
Side-by-side comparison
| Tirzepatide | Retatrutide | |
|---|---|---|
| Receptors | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Maker | Eli Lilly | Eli Lilly |
| FDA status | Approved | Investigational |
| Highest dose tested/approved | 15 mg weekly (label max) | 12 mg weekly (trial) |
| Key result | −20.9% at 72 wk (SURMOUNT-1) | −22.6% at 80 wk (TRIUMPH-3, 12 mg) |
| Legal access | Prescription | Clinical trials only |
Complete comparison (2026)
Key takeaways
- Only tirzepatide can be legally prescribed.
- Trials differ in population and length.
- Retatrutide sold online is not the trial drug.
What are Tirzepatide and Retatrutide?
Tirzepatide is a once-weekly peptide from Eli Lilly that activates both GIP and GLP-1 receptors; it is FDA-approved as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management and for moderate-to-severe obstructive sleep apnea with obesity.
Retatrutide is an investigational once-weekly peptide from Eli Lilly that activates three receptors — GIP, GLP-1 and glucagon — and is in Phase 3 trials for obesity and related conditions; it is not FDA-approved.
Mechanism differences
Both activate GIP and GLP-1 receptors; retatrutide additionally activates the glucagon receptor, which may increase energy expenditure.
Effectiveness
SURMOUNT-1: −20.9% at 72 weeks on tirzepatide 15 mg. TRIUMPH-3: −22.6% at 80 weeks on retatrutide 12 mg in adults with severe obesity and cardiovascular disease; TRIUMPH-2 (type 2 diabetes): −20.8% on 12 mg.
Side effect profiles
Both are GI-dominant. Retatrutide trials also reported dysesthesia (altered skin sensation) more often than placebo, and discontinuations for adverse events up to 13.5%.
Dosing & administration
Tirzepatide: label escalation from 2.5 mg to 15 mg. Retatrutide: trial escalation from 2 mg to 4, 9 or 12 mg.
Cost
Tirzepatide: brand pricing via pharmacies and Lilly programs. Retatrutide: no legal price exists.
FDA & regulatory status
Tirzepatide approved; retatrutide investigational and, per Lilly, cannot be legally sold or marketed for human use.
Who should choose which
Only one of these is an option outside a trial. Talk to a prescriber; ask about trial enrollment for retatrutide.
What the evidence does not show
- That retatrutide is safer or better than tirzepatide — no head-to-head data published.
- Retatrutide cardiovascular benefit.
Frequently asked questions
Is retatrutide better than tirzepatide?
Retatrutide produced somewhat higher average weight loss in its trials, but no head-to-head trial has been published and retatrutide is not approved.
When will retatrutide be available?
Lilly plans to submit a BLA in Q1 2027; approval timing would depend on FDA review.
References
- Tirzepatide Once Weekly for the Treatment of Obesity
- ZEPBOUND (tirzepatide) prescribing information
- Tirzepatide — PubChem compound summary (CID 166567236)
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
- Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity
- Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials
- TRIUMPH-2 (NCT05929079)
- TRIUMPH-3 (NCT05882045)
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