Tirzepatide vs retatrutide

Tirzepatide is an FDA-labeled dual GIP and GLP-1 receptor agonist, while retatrutide is an investigational agonist of the GIP, GLP-1 and glucagon receptors that, according to 2026 trial reports, is still under study. ^1,2 No head-to-head trial of the two was identified, so the comparison below sets each agent's own placebo-controlled trials side by side and flags the differences in design. ^3,4

Tirzepatide

FDA-approved

Retatrutide

Investigational

Side by side

Field	Tirzepatide	Retatrutide
Class	GIP receptor and GLP-1 receptor agonist ¹	GIP, GLP-1 and glucagon receptor agonist ⁴
Mechanism / receptors	Activates the GIP and GLP-1 receptors; the label describes appetite-related brain regions as sites where both receptors are found. ¹	Described in preclinical and phase 1 work as a triple agonist peptide; in vitro it showed balanced glucagon- and GLP-1-receptor activity with more GIP-receptor activity. ⁵
Origin	Based on the GIP sequence with a C20 fatty diacid. ¹	Synthetic investigational peptide (LY3437943). ⁵
Half-life	Approximately 5 days (per label). ¹	A review of phase 1 and 2 data reported a mean half-life of approximately 6 days. ⁶
Highest trial phase	Approved (phase 3 SURMOUNT program) ³	Phase 3 (TRIUMPH and TRANSCEND programs) ^4,7
FDA status	Approved for chronic weight management and obstructive sleep apnea in adults with obesity (Zepbound). ¹	Described as under investigation in 2026 phase 3 reports; no FDA label was identified in the sources reviewed. ²
Published outcomes (weight)	SURMOUNT-1, 72 weeks, no diabetes: -15.0% to -20.9% across three dose arms vs -3.1% with placebo. ³	TRIUMPH-1, 80 weeks, no diabetes: -17.6%, -23.7% and -25.0% across the 4, 9 and 12 mg arms vs -3.9% with placebo. ⁴
Published outcomes (other)	The label also lists moderate to severe obstructive sleep apnea in adults with obesity as an indication. ¹	TRIUMPH-1 also reported WOMAC knee-pain and apnea-hypopnea index changes in osteoarthritis and sleep-apnea subgroups. ⁴
Safety signals	Boxed warning for thyroid C-cell tumors in rats; gastrointestinal reactions most common. ¹	Gastrointestinal events most common; dose-dependent heart-rate increases in phase 2; hypotension and dysesthesia more frequent than placebo in TRIUMPH-2. ^2,8
Evidence level	Regulatory and randomized phase 3 human evidence ^1,3	Randomized phase 2 and phase 3 human trials; no regulatory label identified ^4,8

Tirzepatide: what the data says

SURMOUNT-1 randomized 2,539 adults with obesity or overweight, without diabetes, to once-weekly tirzepatide 5, 10 or 15 mg or placebo for 72 weeks. ³ Mean weight change at week 72 was -15.0%, -19.5% and -20.9% versus -3.1% with placebo, and adverse events led to discontinuation in 4.3%, 7.1% and 6.2% of the three tirzepatide arms versus 2.6% with placebo. ³

The Zepbound label's boxed warning describes thyroid C-cell tumors in rats at clinically relevant exposures and states that human relevance has not been determined. ¹

Retatrutide: what the data says

In a phase 2 trial of 338 adults with obesity, participants received retatrutide (arms from 1 mg to 12 mg) or placebo once weekly for 48 weeks; mean weight change at 48 weeks was -8.7% in the 1 mg group and -24.2% in the 12 mg group versus -2.1% with placebo. ⁸ Gastrointestinal adverse events were dose-related and mostly mild to moderate, and dose-dependent heart-rate increases peaked at 24 weeks and declined thereafter. ⁸

In TRIUMPH-1, a phase 3 trial in 2,339 adults with obesity and without diabetes, participants received retatrutide 4, 9 or 12 mg or placebo once weekly for 80 weeks. ⁴ Mean weight change was -17.6%, -23.7% and -25.0% versus -3.9% with placebo. ⁴ In TRIUMPH-2, which enrolled adults with obesity and type 2 diabetes, weight change at week 80 was -11.9%, -16.8% and -18.8% versus -5.1% with placebo, and discontinuation due to adverse events or death occurred in 12% (9 mg), 8% (12 mg), 4% (4 mg) and 5% (placebo). ²

Key research differences

Receptor profile: tirzepatide is a dual GIP/GLP-1 receptor agonist, whereas retatrutide adds glucagon-receptor agonism, which preclinical work linked to increased energy expenditure in obese mice. ^1,5
Regulatory status differs: tirzepatide has an FDA label (Zepbound), while retatrutide was described as still under investigation in 2026 phase 3 reports. ^1,2
Trial length differs: SURMOUNT-1 lasted 72 weeks and TRIUMPH-1 lasted 80 weeks, and the trials had separate placebo groups (-3.1% and -3.9%), so percentages are not a direct comparison. ^3,4
Retatrutide trials reported dose-dependent heart-rate increases in phase 2 and hypotension and dysesthesia signals in TRIUMPH-2; the tirzepatide label's adverse-reaction table lists gastrointestinal, injection-site and hypersensitivity reactions among its common events. ^1,2,8
Reported half-lives are similar in magnitude, approximately 5 days on the tirzepatide label and approximately 6 days for retatrutide in a review of early-phase data. ^1,6

Where the evidence is limited

No head-to-head trial of tirzepatide and retatrutide was identified in the sources reviewed. ^3,4 Retatrutide's phase 3 data are recent, long-term safety has not been established, and its regulatory evaluation has not been completed in the sources reviewed. ^2,4 The retatrutide half-life figure comes from a narrative review of early-phase data rather than from a prescribing label. ⁶

Frequently asked questions

Is retatrutide approved by the FDA?

In the sources reviewed, retatrutide is described as under investigation for obesity, type 2 diabetes and related conditions, and no FDA label was identified. ^2,7

Have tirzepatide and retatrutide been compared in the same trial?

No head-to-head trial was identified. ^3,4 Each agent has been studied against placebo in separate trials with different durations (72 weeks for SURMOUNT-1, 80 weeks for TRIUMPH-1). ^3,4

What does the third receptor in retatrutide do?

Preclinical work in obese mice reported that glucagon-receptor-mediated increases in energy expenditure added to the calorie-intake reduction attributed to GIP- and GLP-1-receptor activity; this is animal data and has not been established as the mechanism in humans. ⁵

What safety signals have been reported for retatrutide in trials?

The phase 2 obesity trial reported dose-dependent heart-rate increases that peaked at 24 weeks, and TRIUMPH-2 reported hypotension and dysesthesia more often than with placebo. ^2,8 Gastrointestinal events were the most common adverse events across the reports. ^2,4,8

References

ZEPBOUND (tirzepatide) injection, prescribing information FDA label (DailyMed). 2026
Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2) Lancet. 2026
Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) N Engl J Med. 2022
Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity (TRIUMPH-1) N Engl J Med. 2026
LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept Cell Metab. 2022
The First Triple Agonist for Antiobesity: Retatrutide Cardiol Rev. 2024
Efficacy and safety of retatrutide in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1) Lancet. 2026
Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial N Engl J Med. 2023

For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement. This page compares published research and is not medical advice or a recommendation.