The two most-studied incretin molecules, compared on mechanism, phase 3 trial results, and regulatory status — using the published data, honestly framed.
Retatrutide's headline number is bigger — 28.3% mean weight loss versus 20.9% for tirzepatide — and its triple-receptor design (adding glucagon to GIP/GLP-1) is the reason researchers are watching it closely. Tirzepatide's evidence base is deeper — its molecule is the active ingredient in already-approved medicines, with years of large trials and real-world use behind it. One is the stronger candidate on paper; the other is the proven quantity. Which matters more depends on what a researcher is studying.
| Tirzepatide | Retatrutide | |
|---|---|---|
| Mechanism | Dual GIP / GLP-1 receptor agonist | Triple GIP / GLP-1 / glucagon receptor agonist |
| Headline trial | SURMOUNT-1 (phase 3) | TRIUMPH-1 (phase 3) |
| Mean weight loss | 20.9% at 72 weeks, 15 mg | 28.3% at 80 weeks, 12 mg |
| Regulatory status | FDA-APPROVED The medicine is approved; this vial is sold strictly as a research chemical. | PHASE 3 |
| TrueNorth from | C$35 (10 mg) | C$49 (10 mg) |
| View Tirzepatide | View Retatrutide |
Tirzepatide activates the GIP and GLP-1 receptors — the "dual agonist" that made it the benchmark for the field. GLP-1 suppresses appetite and slows gastric emptying; GIP adds further appetite and metabolic effects.
Retatrutide adds a third target: the glucagon receptor. Glucagon raises energy expenditure, which is the hypothesized driver of retatrutide's larger headline weight loss. The trade-off under investigation is tolerability — more pharmacology per molecule means more to watch in the safety data as phase 3 completes.
SURMOUNT-1 randomized 2,539 adults with obesity to tirzepatide or placebo for 72 weeks. Mean weight loss at the 15 mg dose: 20.9%. This is one of the largest obesity trial datasets ever assembled, with extensive secondary endpoints and follow-up analyses.
TRIUMPH-1 tested retatrutide 12 mg over 80 weeks in adults without diabetes. Mean weight loss: 28.3% — the largest headline figure reported for any incretin to date. The program is still in phase 3, so the safety database is smaller and shorter than tirzepatide's.
Side effects for both are dominated by dose-dependent gastrointestinal events (nausea, vomiting, diarrhea) — the class signature of incretins, generally worst during dose escalation.
On headline trial numbers, yes — 28.3% mean weight loss (TRIUMPH-1, 12 mg, 80 weeks) versus 20.9% (SURMOUNT-1, 15 mg, 72 weeks). But these are separate trials with different populations and durations, so the gap is directional, not precise. Retatrutide is also investigational, with a smaller and shorter safety database.
No. As of 2026, no published trial has randomized participants directly between the two. Any comparison you've seen is an across-trial comparison, which is useful for orientation but weaker evidence than a head-to-head.
It is in phase 3 trials and has not been submitted for or granted marketing authorization anywhere yet. Tirzepatide's molecule, by contrast, is the active ingredient in medicines regulators have already approved.
At TrueNorth, tirzepatide starts at C$35 (10 mg) and retatrutide at C$49 (10 mg) before volume discounts. Price per milligram falls on larger sizes for both.
All compounds are sold strictly as laboratory research chemicals — not for human consumption. Trial figures are mean changes in the cited trial populations; see the science guide for context.
