Metabolic
Retatrutide
Also known as LY3437943
Investigational; phase 3 trials reported in 2026, FDA filing planned for early 2027
In simple words: An experimental once-a-week injection that acts on three appetite and metabolism hormones at the same time.
How it works
It switches on the GLP-1 and GIP receptors (which lower appetite and help insulin work) and the glucagon receptor (which raises energy use and helps the liver burn fat).
Targets: GIP receptor, GLP-1 receptor, Glucagon receptor · Class: Triple GIP / GLP-1 / glucagon receptor agonist
Uses, latest studies & pairings
Typically used for
- Obesity: the main use being tested, in the TRIUMPH phase 3 program.
- Type 2 diabetes, knee osteoarthritis pain with obesity, heart disease with obesity, fatty liver and kidney disease (in trials).
- It is also sold online as a “research chemical” for weight loss. Those products are unregulated and their contents are unverified.
Commonly paired with
- Strength training and enough protein (about 1.2–1.6 g per kg of body weight a day, unless your doctor says otherwise) to protect muscle while losing weight.
- Not combined with other GLP-1 medicines: they work on the same receptors, so stacking adds side effects, not safety.
- Diarrhea and nausea were the most common side effects, so fluids and electrolytes matter while the dose is being raised.
Latest studies & news
- Jul 2026
TRIUMPH-2 (type 2 diabetes): about 13–21% weight loss at 80 weeks, with HbA1c down by up to 1.6 points. TRIUMPH-3 (obesity with heart disease): up to 22.6% weight loss. About 10–14% of people on the higher doses stopped because of side effects, versus about 5% on placebo.
Source: Lilly: retatrutide successful in two more phase 3 trials (July 2026) - May 2026
TRIUMPH-1 (2,339 adults with obesity): average weight loss at 80 weeks was 17.6% (4 mg), 23.7% (9 mg) and 25.0% (12 mg), versus 3.9% on placebo. People with severe obesity on the higher doses reached up to about 30% by 104 weeks.
Source: AJMC: retatrutide up to 30% weight loss in TRIUMPH-1 (May 2026) - Dec 2025
TRIUMPH-4 (knee osteoarthritis with obesity): the first phase 3 result, with large weight loss and less knee pain.
- Next
Lilly plans to apply for FDA approval in early 2027. Until then it is not approved anywhere.
What the research shows
Human clinical evidence
Human- Phase 2 trial in adults with obesity: average weight loss reached about 24% after 48 weeks at the highest dose (Jastreboff 2023).
- Phase 3 TRIUMPH-1 (2026, 2,339 adults, 80 weeks): average weight loss of 17.6%, 23.7% and 25.0% on the three doses, versus 3.9% on placebo. TRIUMPH-2 and -3 (diabetes; heart disease) also met their goals.
Animal and lab results suggest what might happen; they don't prove an effect in people.
Safety & what to watch
- Most common side effects were nausea, vomiting, diarrhea and constipation, mainly while the dose was being increased.
- Heart rate rose in a dose-related way during the trial.
- Not approved anywhere. Products sold online as “research” retatrutide are unregulated and their contents are unverified.
Amounts
No dose is given for unapproved substances. If you are considering it, discuss it with a licensed clinician who knows your history and bloodwork.
📦 My peptide supply kit
The supplies I use, in one Amazon list. Only use them for medicines your clinician prescribes. Never share or reuse needles, and put used ones in a sharps container.
Studies & references
Draft profile pending editorial review. Educational only, not medical advice. Never start, stop or change a medicine without your prescriber.