Retatrutide: research, legal status and who sells it

What it is

Retatrutide (development code LY3437943) is an experimental drug that activates three hormone receptors: GIP, GLP-1 and glucagon [8]. Eli Lilly is testing it in the phase 3 TRIUMPH program for obesity, obstructive sleep apnoea and knee osteoarthritis [9].

Research status

In a 48-week phase 2 trial in 338 adults with obesity, average weight loss reached 24.2% in the highest-dose group, compared with 2.1% on placebo; side effects were mainly gastrointestinal, and heart rate rose in a dose-dependent way [8]. The four TRIUMPH trials together enroll more than 5,800 participants [9]. In TRIUMPH-2, published in 2026, adults with obesity and type 2 diabetes lost 11.9% to 18.8% of body weight over 80 weeks, compared with 5.1% on placebo [10]. Diarrhea, nausea, abnormal skin sensations (dysaesthesia) and low blood pressure were more common with retatrutide, and stopping treatment because of adverse events was more frequent at the two higher doses [10].

Regulatory status

Retatrutide is not approved in the US, the UK, the EU or Canada [11][2][3][5]. The FDA states that retatrutide cannot be used in compounding under federal law, is not a component of any FDA-approved drug and has not been found safe and effective for any condition [1]. The agency says it has warned telehealth companies for marketing retatrutide, ingredient distributors for selling it to compounders, and outsourcing facilities for repackaging it [1]. Retatrutide is not named in Australia’s Poisons Standard [6].

Quality and testing considerations

Because no approved retatrutide product exists, every vial sold online is an unapproved product with no regulator-checked reference to compare against. FDA warning letters have rejected “research use only” labeling when a seller’s own marketing shows that the product is meant for people [12]. The FDA also maintains an import alert for GLP-1 active ingredients with potential quality concerns [1]. Independent identity testing by mass spectrometry, plus measured purity and content, is the minimum needed to know what a vial contains.

Where it’s sold

No approved retatrutide product exists; the tables below track the unapproved “research” listings we monitor.