Retatrutide
Retatrutide (LY3437943)
Retatrutide (LY3437943) is a novel triple agonist peptide developed by Eli Lilly that simultaneously targets GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1), and glucagon receptors. It is primarily under clinical investigation for obesity and type 2 diabetes management, having demonstrated exceptional weight loss efficacy in Phase 2 trials with participants losing up to 24% of body weight over 48 weeks. As of 2024, it remains an investigational compound not yet approved by the FDA, though it is being studied and obtained through research channels.
Mechanism of Action
Retatrutide activates three distinct incretin and metabolic receptors: GLP-1R stimulation enhances insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite via central hypothalamic pathways; GIPR activation further potentiates insulin release and may enhance the anorectic effects of GLP-1; glucagon receptor agonism increases energy expenditure and hepatic fat oxidation, counterbalancing potential glucagon-mediated hyperglycemia while promoting lipolysis. This triagonist mechanism creates a synergistic effect on energy balance, carbohydrate metabolism, and fat utilization that surpasses dual agonists like tirzepatide in preclinical and early clinical weight reduction outcomes.
Evidence by Health Goal(15 goals)
Dosing Protocols
Same day each week, subcutaneous injection into abdomen, thigh, or upper arm
Cycle: Dose escalation over 12–24 weeks starting at 2mg; maintenance dose typically 8mg–12mg weekly. No defined off-cycle protocol in clinical data.
Dose escalation is critical to minimize GI side effects: 2mg for 4 weeks, then 4mg for 4 weeks, then 8mg for 4 weeks, then up to 12mg if tolerated. Research-grade vials should be reconstituted in bacteriostatic water and stored at 2–8°C. This compound is not FDA-approved; use outside clinical trials is investigational only.
Safety & Side Effects
Retatrutide carries the class-level safety concerns of GLP-1/GIP receptor agonists including risk of pancreatitis, gallbladder disease, and thyroid C-cell tumors observed in rodent studies; it is an investigational compound not approved for human use outside clinical trials, and sourcing via research peptide vendors involves unknown purity and sterility risks. Phase 2 data showed a generally manageable tolerability profile consistent with other incretin-based therapies, but long-term cardiovascular, oncologic, and metabolic safety data remain incomplete.
Possible Side Effects
- !Nausea (most common, particularly during dose escalation phases)
- !Vomiting, especially at higher doses or with rapid escalation
- !Diarrhea or loose stools during titration periods
- !Constipation during maintenance phase
- !Decreased appetite progressing to significant hypophagia at higher doses
- !Injection site reactions including mild erythema or induration
- !Fatigue and asthenia, particularly early in treatment
- !Potential risk of thyroid C-cell hyperplasia (class concern for GLP-1 agonists; contraindicated in personal or family history of medullary thyroid carcinoma or MEN2)
Interactions
- -May potentiate hypoglycemic effects of insulin or sulfonylureas — dose reduction of concurrent antidiabetic agents may be required
- -Slows gastric emptying, potentially reducing oral drug absorption rate and peak plasma concentrations for time-sensitive medications (e.g., oral contraceptives, thyroid medications)
- -May enhance blood pressure-lowering effects when combined with antihypertensive medications due to weight loss-associated hemodynamic changes
- -Concurrent use with other GLP-1 agonists (e.g., semaglutide, tirzepatide) is contraindicated due to overlapping receptor targets and additive GI toxicity
- -Alcohol consumption may exacerbate nausea and GI side effects and complicate glycemic control
Cost & Where to Buy
Not commercially available as an approved pharmaceutical; research-grade retatrutide from peptide vendors typically costs $180–$520/month depending on dose, vendor quality, and vial concentration. Pricing reflects 4 weekly injections at 8–12mg doses. Pharmaceutical pricing upon potential future approval is unknown but expected to be high, comparable to or exceeding tirzepatide ($1,000+/month before insurance).
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