Retatrutide: what the studies show and when approval could come

Retatrutide is a so-called triple agonist: it activates the receptors for GIP, GLP-1 and glucagon. Tirzepatide (Mounjaro) acts on two of them, semaglutide (Wegovy, Ozempic) on one. The additional glucagon component is considered the reason for the particularly strong weight loss seen in studies.

Like the well-known weight-loss injections, retatrutide is injected under the skin – but so far only in clinical trials. Lilly stresses that the drug is legally available only to participants in its trials. You can find more background in the peptide index entry on retatrutide.

Retatrutide became known through a phase 2 study published in the New England Journal of Medicine in 2023. 338 adults with obesity but without type 2 diabetes received retatrutide at various dose levels or placebo for 48 weeks.

• After 24 weeks: up to −17.5% body weight in the highest dose group (placebo −1.6%)
• After 48 weeks: up to −24.2% (placebo −2.1%)
• Most common side effects: nausea, diarrhoea, vomiting, constipation – dose-dependent, mostly mild to moderate
• Heart rate rose in a dose-dependent way until about week 24 and then fell again
• 6–16% of the retatrutide groups stopped because of side effects, nobody in the placebo group

The doses were set by the study protocol. They are not a recommendation for use outside of studies.

In the phase 3 programme “TRIUMPH”, Lilly is testing retatrutide in several large studies. So far, mainly topline results via press release and congress data have been published; full peer-reviewed publications are partly still to come.

TRIUMPH-4 is notable: here not only weight but knee pain was a primary endpoint. The pain score on the WOMAC questionnaire fell by up to 75.8% with retatrutide and by 40.3% with placebo. This shows that strong weight loss can also noticeably affect conditions like osteoarthritis – although in people who mostly had a BMI of 35 or more.

TRIUMPH-2 will be presented on 30 September 2026 at the EASD congress in Milan. According to Lilly, further phase 3 studies were due to be completed during 2026. Such figures come from tightly controlled studies with medical supervision and cannot be transferred to products of unknown origin.

The side-effect profile is similar to that of other GLP-1 medicines, but pronounced in the higher dose groups:

• Gastrointestinal: In TRIUMPH-1, in the highest dose group 42.4% had nausea (placebo 14.8%), 32.0% diarrhoea, 26.1% constipation and 25.3% vomiting (placebo 4.8%).
• Dysaesthesia (unpleasant abnormal skin sensations, e.g. tingling or burning): 12.5% vs. 0.9% with placebo in TRIUMPH-1, up to 20.9% in TRIUMPH-4. Usually mild to moderate – but a finding not seen in this way with tirzepatide or semaglutide.
• Discontinuation due to side effects: up to 11.3% in TRIUMPH-1 (placebo 4.9%), up to 18.2% in TRIUMPH-4 (placebo 4.0%).
• An increase in heart rate was already observed in phase 2.

Long-term data over several years and results on cardiovascular events are still missing. How to manage gastrointestinal symptoms is covered in Nausea from the weight-loss injection.

In July 2026, Lilly announced it would submit the application for approval to the US regulator FDA in the first quarter of 2027. The review usually takes some time after that.

For Europe, Lilly has (as of September 2026) not named a public date for an application to the EMA. When retatrutide might be available on prescription in Germany, and whether health insurance will pay for it, is therefore open. Any specific months you read about online are speculation.

Online, powder labelled “Retatrutide” is offered as a research chemical “not for human use”. This is not the product from the studies:

• Not approved: According to Lilly, no medicine containing retatrutide is approved anywhere in the world; it may not be sold to consumers.
• Not from Lilly: Lilly does not make any “research” products. Origin, manufacture and storage are unknown.
• Quality unchecked: No authority checks content, purity, sterility or contamination. A seller’s certificate of analysis is no guarantee – more on this in Peptide quality and COA.
• Legal risks: In August 2026, Lilly filed lawsuits against sellers and says it has reported more than 14,000 websites, ads and posts in more than 100 countries. What this means for buyers in Germany is explained in Research peptides: what is legal?

The study results only apply to tested study material under medical supervision. If you want to lose weight, approved medicines such as tirzepatide or semaglutide are alternatives with a known safety profile – talk to your doctor about them. This article is general information, not medical or legal advice.