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Research in plain language

Retatrutide

Retatrutide

What it is

Retatrutide (LY3437943) is a once-weekly injectable peptide developed by Eli Lilly that activates three receptors at once: the GIP, GLP-1, and glucagon receptors (a "triple agonist"). In studies it has been examined for body-weight reduction in obesity, blood-sugar control in type 2 diabetes, and reduction of liver fat in metabolic-dysfunction-associated steatotic liver disease (MASLD).

Dosing Reference from Studies

Mixed (human and animal)Human trial dose

0.5 mg once weekly (human) to 12 mg once weekly (human)

Dose in studies

Discussed in research communities 1-2 titrating up to 12 mg/week (SC)

Reference from peptide forums and community discussions. Not a recommendation, not based on studies, and not an established human protocol.

No established human protocol

Dosing Reference from StudiesCalculate syringe volume ->

How studies used it

Model
Mouse (C57BL/6-based KPCY pancreatic cancer and Lewis lung carcinoma, LLC, allograft models)
Studied for
Obesity-associated cancer progression (pancreatic and lung tumor growth), plus body-weight effect
Dose
30 nmol/kg per dose, which is about 0.14 mg/kg per dose (retatrutide molecular weight ~4731 g/mol: 30 nmol/kg x 4731 ng/nmol = ~141,900 ng/kg = ~0.142 mg/kg)
Dosing
Every other day, starting 14 days before tumor-cell injection and continued; a separate withdrawal group was treated for 14 days only
Route
Subcutaneous
Duration
About 2 weeks of pre-treatment plus continued dosing through tumor growth (withdrawal arm: 14 days)

Effects measured: Reported a 14-fold reduction in pancreatic (KPCY) tumor volume and a 17-fold reduction in lung (LLC) tumor volume versus vehicle controls. Body weight fell by about 38% of baseline in the pancreatic model and about 41% in the lung model, plateauing after roughly 2 weeks. Anti-tumor benefit reportedly persisted after drug withdrawal despite weight regain.

Side effects: No specific adverse events were reported in the treated mice in this study.

Sources: Marathe SJ, et al. Incretin triple agonist retatrutide (LY3437943) alleviates obesity-associated cancer progression. NPJ Metab Health Dis. 2025.

Model
Human, adults with obesity (BMI >=30, or 27 to <30 with a weight-related condition); n=338, 51.8% male
Studied for
Obesity / weight loss
Dose
Mean baseline body weight in this trial was 107.73 kg (BMI 37.34). Weekly doses convert to roughly: 1 mg = ~0.009 mg/kg/week; 4 mg = ~0.037 mg/kg/week; 8 mg = ~0.074 mg/kg/week; 12 mg = ~0.111 mg/kg/week (absolute mg divided by 107.73 kg)
Dosing
Once weekly, with dose escalation (some groups started at 2 mg or 4 mg)
Route
Subcutaneous
Duration
48 weeks

Effects measured: Mean weight change at 48 weeks: placebo -2.1%; 1 mg -8.7%; 4 mg -17.1%; 8 mg -22.8%; 12 mg -24.2%. Proportion losing >=15% of body weight: 2% placebo, 60% (4 mg), 75% (8 mg), 83% (12 mg).

Side effects: Most common adverse events were gastrointestinal (nausea, diarrhea, vomiting), dose-related and mostly mild to moderate. Dose-dependent increases in heart rate peaked at 24 weeks then declined.

Sources: Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med. 2023.

Model
Human, adults with type 2 diabetes (age 18-75, baseline HbA1c 7.0-10.5%, BMI 25-50; mean baseline HbA1c 8.27%); n=281
Studied for
Type 2 diabetes (blood-sugar control) and body weight
Dose
The paper's own mean baseline body weight was not accessible to me, so this mg/kg is an estimate, not the trial's reported mean. Using an assumed ~95 kg for this BMI ~35 cohort: 0.5 mg = ~0.005 mg/kg/week; 4 mg = ~0.042 mg/kg/week; 8 mg = ~0.084 mg/kg/week; 12 mg = ~0.126 mg/kg/week. Verified absolute weekly maintenance doses were 0.5, 4, 8, and 12 mg.
Dosing
Once weekly, with various escalation schedules (comparators: placebo and dulaglutide 1.5 mg weekly)
Route
Subcutaneous
Duration
24 weeks primary endpoint, with 36-week data also reported

Effects measured: HbA1c reduction at 24 weeks: placebo -0.01%; 0.5 mg -0.43%; 4 mg -1.30 to -1.39%; 8 mg -1.88 to -1.99%; 12 mg -2.02% (dulaglutide -1.41%). Weight change at 36 weeks: 0.5 mg -3.19%; 4 mg -7.92 to -10.37%; 8 mg -16.34 to -16.81%; 12 mg -16.94%.

Side effects: Mild-to-moderate gastrointestinal events (nausea, diarrhea, vomiting, constipation) reported in 35% (67/190) of retatrutide participants overall, dose-related (range ~13% to 50% across doses), versus 13% placebo and 35% dulaglutide. No severe hypoglycemia and no deaths.

Sources: Rosenstock J, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a phase 2 trial. Lancet. 2023.

Model
Human, adults with MASLD and >=10% baseline liver fat (substudy of the phase 2 obesity trial); n=98
Studied for
MASLD / liver fat reduction (and body weight)
Dose
Mean baseline body weight in this substudy was 110.2 kg (BMI 38.4). Weekly doses convert to roughly: 1 mg = ~0.009 mg/kg/week; 4 mg = ~0.036 mg/kg/week; 8 mg = ~0.073 mg/kg/week; 12 mg = ~0.109 mg/kg/week (absolute mg divided by 110.2 kg)
Dosing
Once weekly, with dose escalation
Route
Subcutaneous
Duration
48 weeks (liver-fat primary endpoint assessed at 24 weeks)

Effects measured: Relative liver-fat reduction at 24 weeks: placebo +0.3%; 1 mg -42.9%; 4 mg -57.0%; 8 mg -81.4%; 12 mg -82.4%. Normalization of liver fat to <5% at 24 weeks: 0% placebo, 27% (1 mg), 52% (4 mg), 79% (8 mg), 86% (12 mg). Weight change at 48 weeks: placebo -0.1%; 1 mg -8.6%; 4 mg -16.3%; 8 mg -23.8%; 12 mg -25.9%.

Side effects: Transient, generally mild-to-moderate gastrointestinal events were the most frequent adverse events, more common in the 8 mg and 12 mg groups. Per-event frequencies (nausea, diarrhea, vomiting) were not itemized separately in the accessible text.

Sources: Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nat Med. 2024.

How solid the evidence is

Honest summary: One study here is in mice (Marathe 2025, tumor and weight effects) and three are human phase 2 trials (obesity, type 2 diabetes, MASLD substudy). The mouse cancer findings are early preclinical signals only and should not be read across to humans. The three human trials are randomized and placebo-controlled but are all phase 2 (mid-stage), industry-sponsored, and authored largely by Eli Lilly employees and Lilly-funded investigators, so sponsorship bias should be assumed. Dose conversions: the obesity trial (mean baseline weight 107.73 kg, verified from ClinicalTrials.gov NCT04881760) and the MASLD substudy (mean baseline weight 110.2 kg, verified from the published full text) gave reliable mg/kg figures. The type 2 diabetes trial's own reported mean baseline body weight was not accessible in any source I could reach (abstract and ClinicalTrials.gov baseline tables report HbA1c and BMI eligibility but not weight in kg), so its mg/kg numbers are explicitly an estimate using an assumed ~95 kg, not the paper's reported mean; treat those as approximate. The originally suggested phase 1 study (Coskun 2022, PMID 35985340) was verified for title/authors/journal/year, but its indexed abstract did not carry granular per-dose and per-side-effect data, and the full text was paywalled, so I dropped it in favor of the three weight-anchored phase 2 trials to avoid reporting unverified numbers. Important: there is no established human dosing protocol for retatrutide for any use; it is an investigational drug not approved by EMA or FDA, and the weekly mg doses above are trial-defined research doses, not a recommended regimen. All measured effects are study findings, not promises of benefit; gastrointestinal side effects were consistently dose-related across the human trials. Update beyond this section's earlier cut-off: the MASLD finding above is a published phase 2a trial (Sanyal 2024, PMID 38858523, -82.4% relative liver fat at 12 mg/24 weeks), not a mere expectation; and the pivotal phase 3 obesity trial TRIUMPH-1 (NCT05929066) reported a mean -28.3% body weight at 80 weeks (up to -30.3% at 104 weeks) with all doses meeting the primary and key secondary endpoints, but this is an Eli Lilly topline press release from 21 May 2026 and is not yet peer-reviewed. Regulatory status: no NDA had been filed as of mid-2026, with the earliest filing expected around Q4 2026, so retatrutide remains unapproved. Anti-doping note: as an unapproved substance, retatrutide falls under WADA class S0 and is therefore prohibited at all times for athletes in competition and out of competition.

Sources

Frequently asked questions

What is Retatrutide?

Retatrutide (LY3437943) is a once-weekly injectable peptide developed by Eli Lilly that activates three receptors at once: the GIP, GLP-1, and glucagon receptors (a "triple agonist"). In studies it has been examined for body-weight reduction in obesity, blood-sugar control in type 2 diabetes, and reduction of liver fat in metabolic-dysfunction-associated steatotic liver disease (MASLD).

Is Retatrutide legal to buy in the EU?

Retatrutide is sold strictly for laboratory research use. In the European Union it can be purchased as a research chemical, and it is not approved or intended for human or veterinary use. You are responsible for compliant handling in your country.

Where can I buy Retatrutide in Europe?

You can buy Retatrutide from PeptidesDirect, an EU-based shop that dispatches fast, tracked DHL parcels from within Europe. Every batch comes with a third-party Janoshik certificate of analysis (HPLC purity and mass-spectrometry identity), and selected batches also carry our own independent Liquilabs lab testing, all verifiable online before you buy.

Buy Retatrutide (for research use)

Study data, research use only. No established human dosing protocol.