Retatrutide: research protocol, dosing & reconstitution
Also known as: LY3437943
Quick answer
What is Retatrutide?
Retatrutide is an investigational triple agonist that activates the GLP-1, GIP, and glucagon receptors simultaneously. In Phase 2 trials it produced roughly 24% average weight loss at 48 weeks — the largest figure reported for any compound in the class. It is not approved anywhere and remains in Phase 3 trials.
What Retatrutide is
Retatrutide (LY3437943) extends the incretin approach one step further than tirzepatide: alongside GLP-1GLP-1 (glucagon-like peptide-1)A gut hormone that stimulates insulin release, slows stomach emptying, and reduces appetite. GLP-1 receptor agonists such as semaglutide are studied and prescribed for metabolic regulation.See glossary → and GIP activation, it also activates the glucagon receptorReceptorA protein on or inside a cell that binds specific signaling molecules and triggers a response. Most peptides work by binding particular receptors.See glossary →, which increases energy expenditure — attacking weight from both the intake and expenditure sides.
It is an investigational compound with no approval in any country. Research vendors sell lyophilizedLyophilizedFreeze-dried. Peptides are shipped as a lyophilized powder ('puck') because the dry form is far more stable than a solution. It must be reconstituted before use in research.See glossary → retatrutide — commonly 5 mg or 10 mg vialsVialThe small sealed glass container peptides are supplied in, topped with a rubber septum that a syringe needle can pass through.See glossary → — strictly as Research Use OnlyRUO (Research Use Only)A regulatory classification meaning a product is sold strictly for laboratory research and is not approved, labeled, or intended for human or veterinary use.See glossary →.
Mechanism of action
GLP-1 and GIP activation reduce appetite and improve insulin dynamics; glucagon-receptor activation raises hepatic energy expenditure and fat oxidation. In the Phase 2 obesity trial published in the New England Journal of Medicine, the 12 mg dose produced a mean weight reduction of 24.2% at 48 weeks — without an apparent plateau at trial end [1].
Because it is pre-approval, the full safety picture is still being established in Phase 3 — a materially different evidence position from semaglutide or tirzepatide.
What researchers study Retatrutide for
- Triple-incretin mechanism and energy-expenditure studies
- Weight management research (Phase 3 ongoing)
- Hepatic fat (MASLD/NAFLD) research — notable Phase 2 liver-fat reductions
- Glycemic control research
What dose of Retatrutide do researchers use?
Research literature commonly references doses of Titrated: ~2 mg/wk start, stepped up to maintenance in trials. This is not a recommendation — the table below summarizes protocols as they appear in published literature and trial designs.
| Context | Dose | Frequency | Duration |
|---|---|---|---|
| Phase 2 trial titration reference | 2 mg start → stepped to 4, 8, or 12 mg | Once weekly, escalated every 4 weeks | 48-week trial |
← Swipe to see the full table
Half-life and dosing timing
Half-life: ~6 days (once-weekly dosing). Route referenced in research: Subcutaneous, weekly. Half-lifeHalf-lifeHow long it takes for half of a compound to be eliminated from the body. Half-life determines how often researchers dose a compound in protocols.See glossary → around 6 days — once-weekly dosing. Trial arms escalated every 4 weeks, the same steady-state logic as other weekly incretins.
Titration: start low, go slow
Trials started at 2 mg weekly (some arms 1 mg) and escalated stepwise every 4 weeks. Given the compound's potency and investigational status, the literature emphasizes slow escalation more strongly than for any other compound on this site.
Skip the Retatrutide math
Enter vial size, water volume, and target dose — the free calculator returns concentration, injection volume, and exact U-100 syringe units.
How is Retatrutide reconstituted?
| Vial size | BAC water | Concentration | Worked example |
|---|---|---|---|
| 10 mg | 2 mL | 5 mg/mL | 2 mg = 0.4 mL = 40 units on a U-100 syringe |
| 5 mg | 2 mL | 2.5 mg/mL | 2 mg = 0.8 mL = 80 units on a U-100 syringe |
Add 2 mL of bacteriostatic waterBAC water (bacteriostatic water)Sterile water containing 0.9% benzyl alcohol, which suppresses bacterial growth. It is the standard diluent used to reconstitute lyophilized peptides for multi-dose research vials.See glossary → to a 10 mg vial: 10 ÷ 2 = 5 mg/mL. A 2 mg dose is 2 ÷ 5 = 0.4 mL — 40 units on a U-100 syringeU-100 syringeAn insulin syringe calibrated so that 100 units equal 1 mL. The standard syringe referenced in peptide research; each unit equals 0.01 mL.See glossary →.
New to the process? Read the full step-by-step reconstitution guide.
How long does reconstituted Retatrutide last?
Lyophilized: refrigerate. ReconstitutedReconstitutionThe process of mixing a freeze-dried (lyophilized) peptide powder with bacteriostatic water to create a solution of known concentration.See glossary →: refrigerate at 2–8°C and use within weeks. Protect from light; do not freeze the solution.
What is Retatrutide stacked with in research?
Run solo. It is already a three-pathway compound; trial literature contains no combination protocols.
Side effects observed in research
Phase 2 reported the class-typical GI profile — nausea, vomiting, diarrhea, reduced appetite — plus dose-dependent heart-rate increases that are still under evaluation in Phase 3. The honest summary: efficacy data is exceptional, safety data is incomplete.
- Nausea
- Vomiting
- Diarrhea
- Appetite loss
Frequently asked questions
Is retatrutide approved anywhere?
No. Retatrutide is in Phase 3 clinical trials and is not approved for any use in any country. Anything sold today is strictly Research Use Only.
How much weight loss did retatrutide show in trials?
A mean of 24.2% at 48 weeks on the 12 mg dose in Phase 2 — the largest reported in the incretin class — and the curve had not plateaued at trial end.
How does retatrutide differ from tirzepatide?
Tirzepatide activates two receptors (GLP-1, GIP); retatrutide adds a third (glucagon), which increases energy expenditure. Retatrutide is also far earlier in the evidence pipeline.
What did trials use as a starting dose?
Phase 2 arms began at 1–2 mg weekly, escalating every 4 weeks. This describes trial design, not a recommendation.
Related research peptides
Semaglutide
A GLP-1 receptor agonist studied and prescribed for glycemic control and weight management.
GLP-1 / MetabolicTirzepatide
A dual GIP/GLP-1 receptor agonist studied and prescribed for glycemic control and weight loss, generally outperforming semaglutide on weight loss in trials.
Healing & RecoveryBPC-157
A synthetic peptide fragment studied for tissue repair, tendon/ligament and gut healing in animal research.
Browse all GLP-1 / Metabolic peptides or start with the beginner’s guide to research peptides.
References
- 1.Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023. PubMed ↗