Weight & metabolism

Retatrutide: record-breaking Phase 3 results & what's next

Research purposes only (investigational) Checked against official sources Oct 16, 2026

Quick facts

What it is: an experimental weekly shot hitting GIP, GLP-1 and glucagon receptors.
Status: research purposes only. Not FDA-approved. Lilly plans to file in Q1 2027.
Evidence: strong trial data. TRIUMPH-1 showed about −24% to −25% average weight at 80 weeks on the top doses.
Dosage: no approved human dose exists. We list only what trials used.
Bottom line: the biggest weight-loss numbers in obesity trials so far.

What is Retatrutide?

Retatrutide is an experimental weekly injection from Eli Lilly. It hits three hormone receptors at once: GIP, GLP-1, and glucagon. That's one more than tirzepatide.

Is Retatrutide FDA-approved?

Not FDA-approved. It is investigational. Lilly reported five positive Phase 3 trials and says it plans to submit for U.S. approval in the first quarter of 2027 (Lilly, July 2026). Nothing sold online today is the Lilly product. "Research" vials are unregulated.

Retatrutide dosage: what the trials used

There is no approved human dose, so we don't give one. Here is what the studies did:

TRIUMPH-1 (PMID 42814954): once-weekly injections under the skin at 4, 9 or 12 mg, for 80 weeks.
Phase 2 (PMID 37366315): weekly doses from 1 to 12 mg. Starting at 2 mg instead of 4 mg partly reduced GI side effects.
Trials stepped doses up gradually under medical supervision, with a pharmaceutical-grade product.

Why online numbers don't match

People copy trial doses but use unregulated vials whose real content is unknown.
"Units" on insulin syringes depend on how a vial was mixed, so the same number means different doses.
Trials escalated slowly for side effects. Online "protocols" often don't.

Good questions to bring to a clinician

What is actually in the product, and has it been third-party tested?
Is there any human evidence for my specific goal, or only animal studies?
Could it interact with my other medicines or conditions?
Is there an FDA-approved option for what I'm trying to treat?
How would we know if it's working, or causing harm?

What the research shows

TRIUMPH-1 (NEJM, 2026): 2,339 adults with obesity, no diabetes, 80 weeks. Average weight change was −17.6% (4 mg), −23.7% (9 mg) and −25.0% (12 mg) vs −3.9% on placebo. It also cut knee-arthritis pain and sleep-apnea events. Side effects were mostly gastrointestinal.
Phase 2 (NEJM, 2023): 338 adults. At 48 weeks the 12 mg group averaged −24.2% vs −2.1% on placebo. Heart rate went up with dose, peaked at 24 weeks, then eased.
TRIUMPH-2 (Lancet, 2026): 1,152 adults with obesity and type 2 diabetes. Lilly reported up to −20.8% average weight loss at 80 weeks.

New to these terms? See the glossary.

Retatrutide FAQ

Is retatrutide FDA-approved?

No. As of October 2026 it is investigational. Lilly says it plans to submit an application to the FDA in the first quarter of 2027.

How much weight do people lose on retatrutide?

In the TRIUMPH-1 trial, average weight change at 80 weeks was −23.7% on 9 mg and −25.0% on 12 mg, vs −3.9% on placebo.

Is retatrutide stronger than tirzepatide?

Its average trial results are bigger, up to −25.0% vs tirzepatide's −20.2% in SURMOUNT-5, though there's no head-to-head trial yet.

Can I buy real retatrutide?

Lilly's retatrutide is only available in clinical trials right now. Products sold online are labeled for research purposes only.

What are retatrutide's side effects?

In trials, mostly gastrointestinal effects like nausea. The Phase 2 trial also saw dose-related heart-rate increases.

Research purposes only. Not FDA-approved for human use, and products vary in quality. Findings above are from the studies cited.

Not medical advice. Education only. We don't sell anything or tell you what to take. Label doses are there so you can follow along with your prescriber. Talk to a licensed clinician about your health.

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