01 / Mechanism

What it actually does.

Retatrutide is a synthetic 39-amino-acid peptide engineered as a balanced agonist at three receptors: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. A C20 fatty-diacid moiety drives albumin binding for a ~6-day half-life and weekly dosing [Coskun 2022].

The GLP-1 and GIP arms reproduce the appetite suppression and glucose-dependent insulin response that have made semaglutide and tirzepatide blockbuster agents. The novel addition is glucagon-receptor agonism. Glucagon stimulates hepatic glucose production and, at sustained low-level agonism, raises basal metabolic rate via increased lipolysis and thermogenesis. Carefully dosed, this gives retatrutide a second lever on energy balance — calories out in addition to calories in.

The risk is mirror-image: too much glucagon agonism would raise blood glucose and undo the GLP-1 benefit. The trial development effort has been about finding the ratio that lifts energy expenditure without worsening glycemia. So far in Phase 2 and now Phase 3 readouts, that balance has held — HbA1c falls alongside weight. See the long read on retatrutide and the next-generation incretins for the full picture.

02 / Expected dosing

Phase 3 schedule.

Week	Subcutaneous dose	Note	Cohort
1–4	2 mg weekly	Initiation	All
5–8	4 mg weekly	Titration step	All
9–12	4 mg → 8 mg weekly	Step toward target	9 mg / 12 mg arms
13+	4 mg maintenance	Maintenance arm	Phase 3 4 mg cohort
17+	9 mg weekly	Mid-dose maintenance	TRIUMPH 9 mg arm
21+	12 mg weekly	High-dose maintenance	TRIUMPH 12 mg arm

Phase 3 readouts (TRIUMPH-4, Q4 2025)

In adults with obesity and knee osteoarthritis at 68 weeks: −26.4% body weight at 9 mg, −28.7% at 12 mg, versus −2.1% on placebo. The 12-mg group averaged 71.2 lbs (32.3 kg) of weight loss — the largest sustained effect ever reported in a randomized incretin trial. WOMAC knee-pain scores dropped up to 75.8%; more than 1 in 8 patients on retatrutide were knee-pain-free at trial end [Eli Lilly 2025].

03 / Expected contraindications

Who is likely excluded.

Personal or family history of medullary thyroid carcinoma (MTC). Class-effect contraindication for all GLP-1-containing agents based on rodent C-cell data.
Multiple endocrine neoplasia syndrome type 2 (MEN 2). Same rationale.
Prior pancreatitis. GLP-1 class signal — exercised caution in Phase 3.
Severe gastroparesis. Drug exacerbates underlying motility problem.
Pregnancy. Long half-life — washout before conception.
Uncontrolled retinopathy. GLP-1 class signal of retinopathy progression with rapid glycemic improvement.

04 / Side effects

What Phase 2/3 showed.

Nausea (~40–50% at 12 mg). Dose-dependent, mostly transient through titration.
Diarrhea, vomiting, constipation. Same GI profile as other incretins, possibly slightly higher at top dose.
Increased heart rate (~3–6 bpm). Class-typical, plus a small additional bump attributable to the glucagon arm's energy-expenditure effect.
Mild transient liver-enzyme rise. Glucagon arm effect; the net hepatic outcome appears favorable (steatosis improves).
New safety signal flagged in 2025 Phase 3: a small but consistent rate of cardiac arrhythmia (sinus tachycardia) cases — being characterized in regulatory review.
Lean-mass loss. Magnitude not yet fully reported but expected to follow GLP-1 class — mitigate with adequate protein and resistance training.

05 / Availability and positioning

When you can get it.

As of May 2026, retatrutide is investigational only — available exclusively inside the TRIUMPH Phase 3 program and a small set of adjacent studies (sleep apnea, cardiovascular outcomes, MASH). Lilly has guided that additional Phase 3 readouts including the 4 mg maintenance dose are expected in 2026, with regulatory filings to follow. Realistic earliest US approval window is late 2026 to 2027, with launch in 2027–2028 depending on FDA review timelines and manufacturing scale-up.

Compounded retatrutide is already circulating in the gray market. Wellness Radar does not recommend this route: identity, purity, and dose accuracy for a peptide this potent are non-trivial issues, and the FDA shortage-exemption framework that made compounded semaglutide briefly viable does not apply to a drug that has never been approved. See the overview of the GLP-1 era for how the next-generation incretin pipeline is sequencing.

Expected positioning at launch: top-of-funnel obesity agent for patients who need >25% weight loss, with significant runway from tirzepatide's ~22% best-case reduction in the tirzepatide-vs-semaglutide comparison. Pricing is expected to parallel Wegovy/Zepbound.

06 / Cost (anticipated)

What it will likely cost.

Source	Form	~Monthly cost (USD)	Note
Brand (anticipated)	Auto-injector pen	$1,000–$1,400	Will parallel Zepbound/Wegovy list pricing
Brand (anticipated, insured)	Auto-injector pen	$25–$100 copay	If covered for obesity
Compounded (gray market)	Research-chemical vial	n/a	Not recommended — no shortage-exemption pathway
Clinical trial	Provided	$0	Currently the only legitimate route

07 / Key references

The evidence base.

Coskun T et al. 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 Metabolism. 2022;34(9):1234–1247. [Coskun 2022]
Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. NEJM. 2023;389(6):514–526. [Jastreboff 2023]
Rosenstock J et al. Retatrutide for Type 2 Diabetes — A Phase 2 Trial. Lancet. 2023;402(10401):529–544. [Rosenstock 2023]
Eli Lilly. TRIUMPH-4: Retatrutide vs placebo in adults with obesity and knee osteoarthritis (68-week Phase 3 readout). November 2025 press release. [Eli Lilly 2025]
ClinicalTrials.gov. NCT05931367 — A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Are Overweight With Weight-Related Medical Problems. TRIUMPH-1 to TRIUMPH-4 registrational program. [NCT05931367]
Sanyal AJ et al. Retatrutide for MASH and Hepatic Steatosis — A Phase 2 Substudy. Nature Medicine. 2024. [Sanyal 2024]

About this profile

Last reviewed against evidence: 2026-05-12. This profile is editorial reference content, not sponsored. Wellness Radar does not run affiliate links on prescription drugs. Retatrutide is currently investigational; the only legitimate access is through Eli Lilly's TRIUMPH-program clinical trials. Educational reference — not a prescription.

Retatrutide