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The dad-test answer
Tirzepatide is FDA-approved and available now. Retatrutide is in Phase 3 trials (TRIUMPH-3 read out in 2025) showing about 24% body weight loss at 48 weeks, but it is not yet approved or commercially available in 2026. If a reader needs to start losing weight today, the answer is tirzepatide.
Who wins for what
| Use case | Who wins, and why |
|---|---|
| available right now |
tirzepatide FDA-approved as Mounjaro (2022) and Zepbound (2023); retatrutide remains investigational pending FDA review. |
| raw weight-loss potential at peak dose |
retatrutide Phase 2 (Jastreboff et al., NEJM 2023) showed 24% loss at 48 weeks - higher than tirzepatide's 22.5% at 72 weeks in SURMOUNT-1. |
| diabetes (Type 2) |
tirzepatide Tirzepatide has full Phase 3 SURPASS data and FDA approval; retatrutide diabetes data is still emerging. |
| established side-effect profile |
tirzepatide Three-plus years of post-market data; retatrutide trial-only data on a triple-receptor agonist is shorter. |
What the head-to-head data shows
Tirzepatide is a dual GIP/GLP-1 agonist; retatrutide is a triple agonist (GIP + GLP-1 + glucagon receptor). The Phase 2 retatrutide trial (Jastreboff et al., NEJM 2023) randomized 338 adults with obesity and reported 17.5% to 24.2% body-weight loss at 48 weeks across dose cohorts - higher than tirzepatide's 72-week SURMOUNT-1 result of 22.5% (Jastreboff et al., NEJM 2022). The Phase 3 TRIUMPH program is ongoing in 2026 with FDA approval pending. Tirzepatide has full FDA approval (Zepbound 2023) and three-plus years of real-world post-market experience. The glucagon-receptor arm of retatrutide may drive incremental fat loss but it also raises questions about glucose handling that the Phase 3 data will resolve.
Our honest call
Don't wait. If a reader needs to lose weight in 2026, tirzepatide is the answer - it's approved, it's available, and the data behind it is mature. Retatrutide may eventually be the better molecule, but "may" and "available next year" are different categories. Once retatrutide is FDA-approved and a few thousand non-trial patients have run it for 6 to 12 months, the calculus changes. Until then, treat tirzepatide as the defensible default and watch for the FDA decision (expected 2026 to 2027). The tirzepatide switcher protocol covers the on-ramp.
Sources and citations
- Jastreboff et al., Retatrutide Phase 2 trial, NEJM 2023 (PMID 37356269)
- Jastreboff et al., SURMOUNT-1 tirzepatide trial, NEJM 2022 (PMID 35658024)
- Aronne et al., SURMOUNT-5 head-to-head, NEJM 2025 (PMID 40374016)
- FDA Zepbound prescribing label (approved Nov 2023)
- Eli Lilly TRIUMPH program clinicaltrials.gov registry
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Last reviewed · 2026-05-07 · Page generated by Protocol One matrix engine. None of this replaces a doctor. Peptides are gray-market in the US for most uses. Talk to a real prescriber before you change anything.