Retatrutide vs. Tirzepatide: Triple Agonist vs. Dual Agonist
Tirzepatide is FDA-approved with three years of real-world data. Retatrutide is still in Phase 3 trials but has posted some of the largest weight loss numbers in any randomized trial. Here is what the evidence actually says, and what it does not.
Table of Contents
Quick Answer
Retatrutide (triple agonist: GLP-1 + GIP + glucagon) has produced larger average weight loss numbers than tirzepatide in trials: 28.7% at 68 weeks in TRIUMPH-4 vs. 22.5% at 72 weeks in SURMOUNT-1. But these are separate trials in different populations. No head-to-head study exists.
Tirzepatide is FDA-approved, widely available, and has extensive Phase 3 and real-world data. Retatrutide is investigational, not yet approved, and introduces a new side effect (dysesthesia) not seen with tirzepatide. For anyone making a treatment decision today, only tirzepatide is a legal option.
At-a-Glance Comparison
| Retatrutide | Tirzepatide | |
|---|---|---|
| Developer | Eli Lilly | Eli Lilly |
| Mechanism | Triple agonist: GLP-1 + GIP + Glucagon | Dual agonist: GLP-1 + GIP |
| FDA Approval Status | Investigational (Phase 3) | Approved (Nov 2023, Zepbound) |
| Brand Name | Not yet approved | Mounjaro (T2D), Zepbound (obesity) |
| Available by prescription? | No | Yes |
| Trial stage | Phase 3 (7 more readouts due 2026) | Approved — full Phase 3 complete |
| Highest dose studied | 12 mg/week | 15 mg/week (approved) |
| Avg. weight loss (best trial arm) | 28.7% at 68 wks (TRIUMPH-4) | 22.5% at 72 wks (SURMOUNT-1) |
| Head-to-head trial data | None vs tirzepatide | vs semaglutide (SURMOUNT-5) |
| Real-world data | None (not approved) | Yes (Optum, SHAPE studies) |
| Dysesthesia signal | 20.9% at 12 mg (Phase 3) | Not observed |
| Nausea (Phase 3) | ~43% at 12 mg | ~31% at 15 mg (SURMOUNT-1) |
| GI discontinuation | Not yet fully characterized | ~4–5% across SURMOUNT trials |
| Thyroid warning | Unknown (monitoring ongoing) | Black box warning (rodent data) |
Retatrutide data: Phase 2 (NEJM 2023) and TRIUMPH-4 topline results (Dec 2025). Tirzepatide data: SURMOUNT-1 (NEJM 2022) and SURMOUNT-5 (NEJM 2025). Cross-trial comparisons are limited by differences in study populations and design.
How They Differ: Mechanism of Action
Both drugs were developed by Eli Lilly and share the GLP-1 and GIP receptor targets. The key distinction is that retatrutide adds glucagon receptor agonism as a third mechanism.
Tirzepatide (GLP-1 + GIP)
- •GLP-1 agonism: suppresses appetite, slows gastric emptying, improves insulin secretion
- •GIP agonism: enhances appetite suppression, improves insulin sensitivity, may promote fat oxidation
- •Dual mechanism creates complementary metabolic effects
- •Well-characterized — full Phase 3 data + 3 years real-world use
Retatrutide (GLP-1 + GIP + Glucagon)
- •All GLP-1 and GIP effects, plus:
- •Glucagon agonism: increases energy expenditure and thermogenesis
- •Glucagon receptor may drive greater liver fat reduction (hepatic fatty acid oxidation)
- •Glucagon's glucose-raising effect is counterbalanced by GLP-1 and GIP co-activation
- •Triple mechanism hypothesis: greater adiposity reduction via multiple independent pathways
Why glucagon agonism is a double-edged addition
Glucagon normally raises blood glucose — the opposite of what you want in metabolic therapy. Retatrutide co-activates GLP-1 and GIP to neutralize this effect. The net result in trials has been improved glucose control despite glucagon agonism. But the glucagon component is also suspected to contribute to the dysesthesia signal seen in TRIUMPH-4. This mechanism is still being characterized across the full Phase 3 program.
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Clinical Evidence: What Trials Show
Retatrutide: Phase 2 + TRIUMPH-4
Phase 2 Trial (NEJM 2023)
Published
NEJM, June 2023
Participants
338 adults
Duration
48 weeks
Population
Obesity/overweight, no T2D
| Dose | Mean weight loss at 48 wks | Achieved ≥15% loss |
|---|---|---|
| 1 mg | −8.7% | N/A |
| 4 mg | −17.1% | 60% |
| 8 mg | −22.8% | 75% |
| 12 mg | −24.2% | 83% |
| Placebo | −2.1% | 2% |
TRIUMPH-4 Phase 3 (Topline, Dec 2025)
Readout
December 2025
Duration
68 weeks
Doses tested
9 mg and 12 mg
Population
Obesity + knee osteoarthritis
Weight Loss
28.7%
12 mg dose average at 68 weeks
26.4%
9 mg dose average at 68 weeks
12 mg: avg. ~71.2 lbs lost
Additional Findings
- +Significant knee pain reduction (OA population)
- +Improved physical function scores
- !Dysesthesia identified as new safety signal
- -Full peer-reviewed publication pending
Tirzepatide: SURMOUNT Program + Real-World Data
SURMOUNT-1 (NEJM 2022) — Pivotal Registration Trial
Published
NEJM, June 2022
Participants
2,539 adults
Duration
72 weeks
Population
Obesity/overweight, no T2D
| Dose | Mean weight loss at 72 wks | Achieved ≥20% loss |
|---|---|---|
| 5 mg | −16.0% | 32% |
| 10 mg | −21.4% | 57% |
| 15 mg | −22.5% | 63% |
| Placebo | −2.4% | 1% |
Beyond SURMOUNT-1: The full evidence picture
- •SURMOUNT-2: T2D population, 15.7% weight loss at 72 weeks
- •SURMOUNT-3: After intensive lifestyle intervention, 26.2% additional loss at 72 weeks
- •SURMOUNT-4: Maintenance trial — 82% regain without continuation
- •SURMOUNT-5: Head-to-head vs semaglutide, 20.2% vs 13.7% (NEJM 2025)
- •Real-world: Optum study (n=20,998 at 6 months), SHAPE study (n=9,916 at 12 months)
The key evidence gap
Retatrutide's 28.7% figure comes from a single Phase 3 topline readout in a population with obesity and knee osteoarthritis. The full publication, peer review, and data transparency are still pending. Tirzepatide's 22.5% comes from a fully published, peer-reviewed trial in 2,539 people with complete safety reporting, and it has been confirmed in multiple independent studies. These numbers are not directly comparable without a head-to-head trial.
Side Effects Comparison
Both drugs share the GLP-1/GIP mechanism, so GI side effects are common to both. The critical difference is that retatrutide has introduced a new side effect category — dysesthesia — not seen with tirzepatide.
| Side Effect | Retatrutide | Tirzepatide |
|---|---|---|
| Nausea | ~43% at 12 mg (TRIUMPH-4) | ~31% at 15 mg (SURMOUNT-1) |
| Diarrhea | ~33% at 12 mg | ~23% at 15 mg |
| Constipation | ~25% at 12 mg | ~17% at 15 mg |
| Vomiting | ~21% at 12 mg | ~11% at 15 mg |
| Dysesthesia | 20.9% at 12 mg; 8.8% at 9 mg | Not observed |
| GI discontinuation | Not fully characterized yet | ~4–5% across SURMOUNT trials |
| Pancreatitis | Rare (monitoring ongoing) | Rare (black box warning) |
| Gallbladder issues | Possible (rapid weight loss) | Possible (rapid weight loss) |
| Thyroid warning | Under investigation (Phase 3) | Black box warning (rodent data) |
| Long-term safety data | Phase 3 only, pending full pub. | 3+ years real-world surveillance |
What is dysesthesia?
Dysesthesia refers to abnormal, sometimes unpleasant skin sensations, including tingling, burning, numbness, or a feeling of something crawling under the skin. It was not observed in retatrutide's Phase 2 trials and appeared as a new signal in TRIUMPH-4, where it occurred in 8.8% of the 9 mg group and 20.9% of the 12 mg group (vs. 0.7% on placebo). Events were generally mild and rarely led to discontinuation, but this signal is under active investigation across the rest of the TRIUMPH program.
The glucagon receptor component of retatrutide is suspected to contribute to this signal. Tirzepatide does not activate the glucagon receptor and does not carry this risk.
GI side effects context:Retatrutide's higher GI rates partly reflect its higher absolute weight loss — more aggressive fat mobilization correlates with more GI disruption. Tirzepatide's GI profile is well-characterized and generally manageable with slow dose escalation. For practical management strategies, see our GLP-1 side effects management guide.
Approval Status and Access
Tirzepatide
- •Approved for type 2 diabetes as Mounjaro (May 2022)
- •Approved for obesity as Zepbound (November 2023)
- •Available at pharmacies nationwide
- •Compounded versions available through telehealth
- •List price: ~$1,069/month (Zepbound); savings card as low as $25/month for eligible patients
- •Insurance coverage growing, inconsistent by plan
Retatrutide
- •Not FDA-approved as of May 2026
- •Not legally available by prescription outside clinical trials
- •7 additional Phase 3 readouts expected in 2026
- •FDA submission timeline not yet announced
- •Working name: potentially Attruby (unconfirmed)
- •No pricing information available
Who Should Consider Each?
Tirzepatide is appropriate if:
- ✓You are ready to start treatment now and meet clinical criteria for obesity medication
- ✓You want a medication with extensive safety data and FDA oversight
- ✓Your insurer covers Zepbound, or you qualify for Lilly's savings program
- ✓You have type 2 diabetes (Mounjaro is also approved for T2D)
- ✓You have tried semaglutide with inadequate results and want to escalate to a dual agonist
- ✓You want access to compounded alternatives at lower cost through telehealth
Retatrutide is not yet an option — but follow it if:
- →You have tried tirzepatide and want to understand what next-generation options may look like
- →You have obesity and knee osteoarthritis (TRIUMPH-4 showed meaningful pain relief alongside weight loss)
- →You want to monitor the remaining TRIUMPH trial readouts expected in 2026
- →You are interested in the glucagon agonism mechanism for potential liver fat benefits (MASLD/NASH)
- →You are a healthcare provider tracking the pipeline for future clinical options
The Bottom Line
Retatrutide is not better than tirzepatide — not yet, and not in a provable way. The trial numbers look larger, but they come from different populations, different durations, and a much thinner evidence base. TRIUMPH-4 is one Phase 3 topline readout. SURMOUNT is five completed Phase 3 trials plus real-world studies. That is not a fair comparison.
What retatrutide does represent is a genuinely different mechanism — triple agonism — and Phase 3 data that, if confirmed across the full trial program, could establish it as the next step forward in obesity pharmacotherapy. The dysesthesia signal warrants monitoring, and seven more trial readouts in 2026 will determine whether the efficacy numbers hold across populations.
For anyone making a treatment decision today: tirzepatide is approved, available, and produces transformative weight loss. A 22.5% average weight loss at 72 weeks is a clinical result no physician would dismiss. The right question is not which trial number is bigger. It is which option you can actually access, afford, and sustain. Compare providers that offer tirzepatide to find a program that fits your situation.
Frequently Asked Questions
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Sources
- 1.Jastreboff AM, et al. "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." N Engl J Med. 2023;389(6):514-526.
- 2.Eli Lilly and Company. "Lilly's triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial (TRIUMPH-4)." Press release. December 2025.
- 3.Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)." N Engl J Med. 2022;387(4):327-340.
- 4.Aronne LJ, et al. "Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5)." N Engl J Med. 2025;393(1):26-36.
- 5.Lilly Investor Relations. "Lilly's phase 2 retatrutide results published in NEJM." June 2023.
- 6.Ludvik B, et al. "Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial." Nature Medicine. 2024.
- 7.FDA. "FDA Approves New Medication for Chronic Weight Management (Zepbound/tirzepatide)." November 2023.