Retatrutide
Also known as LY3437943
A new weight-loss drug still being tested. It works on three hunger and metabolism hormones at once — that's why it's called a "triple agonist".
Quick facts
- Status
- Investigational — not approved yet
- Evidence
- Investigational (phase 2 and phase 3 trials)
- Taken as
- Injection under the skin once a week (in trials)
- Common sizes
- 5 mg, 10 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg
- Category
- GIP/GLP-1/glucagon receptor agonist · weight (investigational)
How it works
Like semaglutide it reduces hunger, but it also acts on glucagon, a hormone that may make your body burn more energy and clear fat from the liver.
What people use it for
- Obesity (in clinical trials)
- Type 2 diabetes (in clinical trials)
What the research shows
- In a large 2026 trial, people on the highest dose lost about 28% of their body weight in 80 weeks.
- These are some of the biggest weight-loss results seen with any drug.
- It is not approved anywhere yet — the long-term safety picture is still being built.
Side effects & risks
- Nausea, diarrhoea, constipation and vomiting — more common at higher doses
- Tingling or unusual skin sensations
- Higher heart rate
- "Research" retatrutide sold online is not the trial drug and may be impure or wrongly dosed
Is it legal?
Investigational — not approved by the EMA, FDA or MHRA as of October 2026 and only legally available through clinical trials. Phase 3 (TRIUMPH) trials have reported positive results; check for updates on regulatory submissions. Products sold online as "research" retatrutide are unregulated and not the clinical-trial drug.
Storage & safe handling
- Mix with bacteriostatic water: let it run slowly down the inside of the vial and swirl gently — never shake.
- Store the mixed vial in the fridge and follow the use-by period on the label.
- Wipe the vial top with alcohol and use a new sterile needle and syringe every time.
- Rotate injection sites so the same spot is not used again and again.
- Put used needles in a sharps container, not the household bin.
- Get medical help for redness that spreads, fever, swelling or trouble breathing.
Open in PepTimerTrack your protocol, calculate how much to draw and get reminders — free.Open in PepTimer
Sources: Jastreboff AM et al., "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial", N Engl J Med 2023; Eli Lilly TRIUMPH-1 phase 3 results (May 2026, ClinicalTrials.gov NCT05929066).
Last updated 12 October 2026. Information — not medical advice. PepTimer does not replace a doctor. Many peptides are not approved medicines in the EU, UK or US. Talk to a qualified healthcare provider before starting, changing or stopping any treatment.
Last updated 12 October 2026. Information — not medical advice. PepTimer does not replace a doctor. Many peptides are not approved medicines in the EU, UK or US. Talk to a qualified healthcare provider before starting, changing or stopping any treatment.