Is retatrutide approved?

No. As of 2026 retatrutide is investigational — it has completed Phase 1 and Phase 2 trials and is in Phase 3 development, but it is not FDA-approved for weight loss, diabetes, or any other use.

How much weight did people lose in the trials?

In the Phase 2 obesity trial (338 adults, 48 weeks), least-squares mean body-weight change was −8.7% at 1 mg, −17.1% at 4 mg, −22.8% at 8 mg, and −24.2% at 12 mg, versus −2.1% for placebo. These are trial results under medical supervision, not a promise of individual outcomes.

What are the main side effects?

In the Phase 2 trial the most common adverse events were gastrointestinal (nausea, diarrhea, vomiting, constipation), mostly mild to moderate and dose-dependent, and a lower starting dose reduced them. Dose-dependent increases in heart rate were also seen, peaking around 24 weeks and then declining.

metabolic

Retatrutide

Retatrutide (LY3437943) is an investigational once-weekly injectable that activates three metabolic receptors at once — GIP, GLP-1, and glucagon. Unlike most peptides in the biohacker space, it has published human randomized controlled trials: a Phase 2 obesity trial reported least-squares mean weight loss up to 24.2% at 48 weeks on the 12 mg dose, and a Phase 2a liver-fat trial reported large reductions in liver fat. As of 2026 it remains investigational and is not FDA-approved; Phase 3 trials are ongoing.

By LetsTalkPeps Staff2 min read● Human RCT evidence

Also known as: LY3437943

Educational content only — this is not medical advice. Retatrutide is an investigational drug studied under medical supervision. Do not attempt to source or self-administer it.

What it is

Retatrutide (development code LY3437943) is a once-weekly injectable peptide that is a triple agonist — it simultaneously activates the receptors for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon. It builds on the same class as GLP-1 drugs (semaglutide) and the dual GIP/GLP-1 drug tirzepatide, but adds glucagon-receptor activity, which is thought to increase energy expenditure and act on liver fat. A Phase 1b study reported a half-life of roughly 6 days, consistent with once-weekly dosing.

What the evidence shows

This is the peptide on the site that earns a human-RCT badge, and it earns it honestly — the claims below come from published, randomized, placebo-controlled human trials.

In the Phase 2 obesity trial (NEJM, 2023; 338 adults, double-blind, placebo-controlled, 48 weeks), least-squares mean body-weight change was −8.7% (1 mg), −17.1% (4 mg), −22.8% (8 mg), and −24.2% (12 mg), compared with −2.1% for placebo. Effects were dose-dependent.

In a separate Phase 2a trial in metabolic dysfunction-associated steatotic liver disease (MASLD) (Nature Medicine, 2024; 98 participants, 48 weeks), the mean relative reduction in liver fat at 24 weeks reached −81.4% (8 mg) and −82.4% (12 mg) versus +0.3% for placebo, and normal liver fat (under 5%) was achieved by 79% (8 mg) and 86% (12 mg) of participants versus 0% on placebo.

An earlier Phase 1b trial in type 2 diabetes (Lancet, 2022) established the safety and pharmacokinetic basis for weekly dosing. Together these are genuine human RCTs — which is exactly why the evidence tier here is not "preclinical."

Risks & unknowns

The most common adverse events across trials were gastrointestinal — nausea, diarrhea, vomiting, constipation — generally mild to moderate and dose-dependent, and partly mitigated by a lower starting dose. Dose-dependent heart-rate increases were also observed, peaking around 24 weeks before declining. Because retatrutide is still in development, its long-term safety, durability of weight loss, and outcomes in broad real-world populations are not yet established — those are what Phase 3 trials are designed to answer.

Legal / regulatory status

Retatrutide is investigational. It has not been approved by the FDA (or other major regulators) for weight management, diabetes, or liver disease, and it is only legitimately available inside clinical trials. Phase 3 studies are ongoing as of 2026. "Retatrutide" sold by research-chemical or gray-market vendors is not the trial drug, is not quality-controlled, and is not authorized for human use.

FAQ

Is retatrutide approved?: No. As of 2026 retatrutide is investigational — it has completed Phase 1 and Phase 2 trials and is in Phase 3 development, but it is not FDA-approved for weight loss, diabetes, or any other use.
How much weight did people lose in the trials?: In the Phase 2 obesity trial (338 adults, 48 weeks), least-squares mean body-weight change was −8.7% at 1 mg, −17.1% at 4 mg, −22.8% at 8 mg, and −24.2% at 12 mg, versus −2.1% for placebo. These are trial results under medical supervision, not a promise of individual outcomes.
What are the main side effects?: In the Phase 2 trial the most common adverse events were gastrointestinal (nausea, diarrhea, vomiting, constipation), mostly mild to moderate and dose-dependent, and a lower starting dose reduced them. Dose-dependent increases in heart rate were also seen, peaking around 24 weeks and then declining.

Retatrutide

What it is

What the evidence shows

Risks & unknowns

Legal / regulatory status

FAQ

References