Retatrutide
Retatrutide (GIP/GLP-1/Glucagon Triple Agonist)
Retatrutide is a triple agonist targeting GIP, GLP-1, and glucagon receptors simultaneously — the most potent pharmacological weight loss agent in clinical development as of 2026. In Phase 2 trials, retatrutide 12mg weekly produced mean weight loss of 24.2% at 48 weeks — surpassing tirzepatide's Phase 3 results. Phase 3 trials are underway. The glucagon component adds a third mechanism: direct hepatic fat mobilisation and enhanced energy expenditure through brown adipose tissue activation.
Mechanism of Action
Retatrutide activates three incretin and metabolic hormone receptors simultaneously. GLP-1 receptor agonism drives appetite suppression, slows gastric emptying, and reduces food intake — the primary mechanism shared with semaglutide and tirzepatide.
GIP receptor agonism potentiates insulin secretion and adds hypothalamic appetite suppression via GIP receptors in the brain — the same dual mechanism as tirzepatide. However, retatrutide's glucagon receptor agonism differentiates it from all existing approved agents.
Glucagon receptor activation drives two critical additional effects: direct hepatic fat mobilisation (glucagon is a potent lipolytic signal in the liver, addressing non-alcoholic fatty liver disease simultaneously) and enhanced thermogenesis via brown adipose tissue activation (increasing resting energy expenditure). This third mechanism is the primary reason retatrutide's weight loss in Phase 2 exceeded all prior GLP-1 class agents.
Research Evidence
Retatrutide is in Phase 3 clinical trials (NCT06052826) as of 2026, following highly positive Phase 2 data. The Phase 2 trial (NCT04881760, n=338) is the strongest weight loss signal from any pharmacological agent in human trials to date.
Retatrutide Phase 2: Triple Agonist for Obesity
338 adults with obesity; retatrutide 12mg weekly produced 24.2% mean body weight reduction at 48 weeks (vs 2.1% placebo). 26% of participants lost ≥30% body weight — approaching surgical outcomes. Dose-dependent effects at 4mg (8.7%) and 8mg (17.5%) also demonstrated.
Typical Research Protocol
Retatrutide is not yet FDA-approved. Phase 3 data is expected in 2026–2027. Use outside clinical trials is experimental. The Phase 2 titration started at 2mg and increased monthly. GI adverse effects are similar in type to tirzepatide but GI tolerability was considered manageable at approved-candidate doses.
Safety Profile
Reported Side Effects
- Nausea
- Vomiting
- Diarrhoea
- Constipation
- Decreased appetite
- Injection site reactions
Contraindications
- History of MEN2 or medullary thyroid carcinoma
- Active pancreatitis
- Pregnancy
- Severe renal impairment (limited data)
Common Research Stacks
Frequently Asked Questions
How much weight can you lose on retatrutide?
Phase 2 data showed 24.2% mean weight loss at 48 weeks with 12mg weekly dosing — the highest pharmacological weight loss outcome published in a human clinical trial. 26% of participants lost ≥30% of body weight. Phase 3 results (expected 2026–2027) will determine whether these Phase 2 findings replicate at scale.
Is retatrutide better than tirzepatide?
In Phase 2, retatrutide 12mg produced ~24% weight loss versus tirzepatide's ~21% in SURMOUNT-1. The glucagon receptor component adds thermogenesis (calorie burning) and hepatic fat mobilisation that tirzepatide lacks. However, Phase 2 vs Phase 3 comparisons have limitations. A direct head-to-head trial has not been published. Retatrutide is not yet approved for clinical use.
What makes retatrutide different from tirzepatide?
Tirzepatide targets two receptors (GIP + GLP-1). Retatrutide targets three: GIP + GLP-1 + glucagon. The glucagon component drives hepatic fat mobilisation (relevant for fatty liver disease) and activates brown adipose tissue thermogenesis — increasing resting energy expenditure. This third mechanism is absent in tirzepatide and appears to be responsible for the additional weight loss beyond the dual-agonist class.
When will retatrutide be FDA approved?
As of 2026, retatrutide is in Phase 3 trials. FDA approval typically follows 1–2 years after Phase 3 trial completion and submission. Optimistic estimates place US approval in 2027–2028, assuming Phase 3 results confirm Phase 2 efficacy and the safety profile remains acceptable. Regulatory decisions may be expedited given the obesity treatment landscape.
Does retatrutide treat fatty liver disease?
Retatrutide's glucagon receptor component directly drives hepatic fat mobilisation — a mechanism relevant to NAFLD (non-alcoholic fatty liver disease) and NASH. Phase 2 data showed significant improvements in liver fat content and hepatic enzyme markers alongside the weight loss. Eli Lilly is running separate trials for MASH (metabolic dysfunction-associated steatohepatitis) as a distinct indication for retatrutide.
Where can I get retatrutide?
Retatrutide is not FDA-approved and is not legally available outside clinical trials in the US. Participating in the ongoing Phase 3 trial (NCT06052826) is the only legitimate access pathway currently. Some research chemical suppliers have offered unapproved versions, but pharmaceutical-grade, safety-tested retatrutide is unavailable outside the clinical trial programme.
Key Research References
- Jastreboff AM et al. (2023). Triple-hormone-receptor agonist retatrutide for obesity. N Engl J Med.
- Lilly EI. (2023). Retatrutide Phase 3 programme (NCT06052826). ClinicalTrials.gov.
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