Lilly New Weight Loss Drug Retatrutide: What We Know So Far

Retatrutide is an experimental once-weekly weight loss injection from Eli Lilly that targets three hormone receptors at once: GIP, GLP-1, and glucagon. In a phase 2 trial, adults with obesity lost up to about 24% of their body weight after 48 weeks on the highest dose. Retatrutide is not FDA-approved, and it cannot legally be prescribed or sold in the United States today.

What Is Retatrutide and How Does It Work?

Retatrutide, also known by the research code LY3437943, is what scientists call a triple agonist. It copies three hormones your gut and pancreas already produce, and each one affects appetite, blood sugar, or metabolism in a different way.

• GLP-1 slows stomach emptying and tells the brain you feel full. Semaglutide (Wegovy, Ozempic) works through this same pathway.
• GIP influences insulin release and how the body stores fat. Tirzepatide (Zepbound, Mounjaro) also uses it.
• Glucagon raises energy expenditure, which researchers believe is part of why retatrutide produced larger weight loss numbers than earlier drugs in the same family.

Retatrutide is a prescription drug candidate, not a supplement. Products sold online with that name are unregulated research chemicals rather than the drug used in trials, and they have not been tested for safety in people. Anyone browsing for peptide supplements for weight loss should know that none of those products are FDA-approved for weight loss in the US.

How Much Weight Did People Lose on Retatrutide?

The most reliable human data so far comes from a phase 2 trial published in the New England Journal of Medicine in 2023. It followed 338 adults with obesity or overweight who did not have diabetes, and it ran for 48 weeks. Average weight loss depended heavily on the dose.

Weekly dose	Average weight loss at 48 weeks
1 mg	About 8.7%
4 mg and 8 mg (pooled analysis)	About 17%
12 mg	About 24.2%
Placebo	About 2%

Those are phase 2 estimates from a single trial, so the final numbers could shift once larger phase 3 studies are complete. Even so, a 24% reduction would place retatrutide among the most effective obesity medications ever tested.

How Retatrutide Compares With Other Weight Loss Drugs

Drug	Maker	Targets	Status	How it is taken
Retatrutide	Eli Lilly	GIP, GLP-1, glucagon	Investigational (phase 3)	Weekly injection
Tirzepatide (Zepbound)	Eli Lilly	GIP and GLP-1	FDA-approved for obesity	Weekly injection
Semaglutide (Wegovy)	Novo Nordisk	GLP-1	FDA-approved for obesity	Weekly injection
Orforglipron	Eli Lilly	GLP-1	Investigational (phase 3)	Daily pill

Dosing is not one-size-fits-all. The same principle explains why increase dose of semaglutide for weight loss is usually done in slow steps rather than all at once: starting low and moving up gradually keeps nausea manageable. Oral semaglutide is also under review for weight loss, so questions about the semaglutide tablet dose for weight loss may have clearer answers in the next year or two.

What Side Effects Did Trial Participants Report?

Retatrutide's side effect profile looks similar to other GLP-1-based drugs. Most complaints were gastrointestinal and tended to fade after a few weeks at a stable dose.

• Nausea
• Diarrhea
• Vomiting
• Constipation
• Injection-site reactions

Some participants stopped treatment because of these effects, especially at higher doses. Heart rate also increased slightly in the trial, which researchers are tracking in the ongoing phase 3 program. Anyone with a history of pancreatitis, gallbladder disease, or certain thyroid conditions should discuss risks with a clinician before considering this class of medication.

When Will Retatrutide Be Available in the US?

Eli Lilly is running the phase 3 TRIUMPH program, a series of large trials that will measure weight loss, cardiovascular outcomes, and safety in thousands of participants. Phase 3 programs of this size typically take several years to read out and submit for review.

Most industry analysts expect a possible FDA decision no earlier than 2027 or 2028, though that timeline could move in either direction. Separately, many people ask when will eli lilly weight loss pill be available, which refers to orforglipron, an oral GLP-1 candidate from the same company rather than retatrutide itself.

What Should You Do While You Wait?

Approved options already exist, including tirzepatide, semaglutide, and older medications such as phentermine or bupropion-naltrexone. A healthcare professional can help you weigh effectiveness, cost, insurance coverage, and side effects for each one.

Be cautious with gray-market injections. Retatrutide is not for sale legally, so anything sold under that name is unverified and may be contaminated or dosed incorrectly. Peptide curiosity is understandable, and questions like does kpv help with weight loss come up often, but no human trials show that KPV produces meaningful weight loss.

Bottom line: retatrutide has produced the strongest weight loss results of any Eli Lilly obesity drug tested so far, but it remains experimental and unavailable to the public.

RELATED PEPTIDE TOPICRetatrutide peptide

COMMON QUESTIONS

Frequently Asked Questions

Is retatrutide available now?

No. Retatrutide is still in phase 3 clinical trials and has not been approved by the FDA for any use. It can only be obtained legally by joining a clinical trial, so any product sold online under that name is unregulated and potentially unsafe.

How much weight can you lose on retatrutide?

In a 48-week phase 2 trial, participants on the highest 12 mg weekly dose lost about 24% of their body weight on average. Lower doses produced smaller results, and the placebo group lost roughly 2%. Final phase 3 numbers are still pending.

Is retatrutide a pill or a shot?

Retatrutide is a once-weekly injection, not a pill. Eli Lilly is separately developing orforglipron, an oral GLP-1 pill, but that is a different drug with its own trial timeline.