23/06/2026
Retatrutide is an investigational once-weekly injectable medication being developed by Eli Lilly.
Mechanism
Retatrutide is unique because it activates three receptors:
* GLP-1 receptor
* GIP receptor
* Glucagon receptor
The glucagon receptor component is what makes retatrutide different from GLP-1 agonists (semaglutide) and dual GIP/GLP-1 agonists (tirzepatide).
Normally, glucagon is known as the hormone that raises blood glucose by stimulating the liver to release glucose. At first glance, activating glucagon receptors seems counterintuitive for treating obesity.
However, glucagon receptors also:
1. Increase energy expenditure
* They stimulate thermogenesis (heat production).
* The body burns more calories at rest.
2. Promote fat oxidation
* The liver and adipose tissue increase utilization of stored fat.
* This may contribute to greater weight loss than GLP-1 agonism alone.
3. Reduce liver fat
* Glucagon signaling can decrease hepatic fat accumulation.
* This has generated interest in treating metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD).
4. May enhance satiety
* The appetite-suppressing effect is primarily from GLP-1 and GIP, but glucagon signaling may contribute indirectly.
Why doesn’t it cause severe hyperglycemia?
Because retatrutide simultaneously activates:
* GLP-1 receptors → increase glucose-dependent insulin secretion and reduce glucagon secretion.
* GIP receptors → enhance insulin secretion.
* Glucagon receptors → increase energy expenditure but tend to raise glucose.
The GLP-1 and GIP effects largely counterbalance the glucose-raising effect of glucagon, allowing the metabolic benefits of glucagon receptor activation while maintaining glycemic control.
A simplified view:
GLP-1 ↓ appetite, ↓ gastric emptying, ↑ insulin
GIP ↑ insulin, may improve adipose metabolism
Glucagon ↑ energy expenditure, ↑ fat burning, ↓ liver fat
The theory behind retatrutide is that GLP-1 + GIP reduce caloric intake, while glucagon increases caloric expenditure. Most current obesity drugs mainly reduce intake; retatrutide attempts to influence both sides of the energy balance equation, which may explain the unusually large weight-loss effects seen in trials.
This “triple agonist” approach appears to produce greater weight loss than currently available GLP-1–based therapies in clinical trials.
Retatrutide is not yet approved by major regulatory agencies. Phase 3 trials for obesity and type 2 diabetes are ongoing.
Weight-loss efficacy
In a phase 2 obesity trial, participants receiving the highest dose achieved approximately 24% mean weight loss at 48 weeks, among the largest effects seen with any anti-obesity medication studied to date. Longer-term studies suggest even greater reductions may be achievable. Phase 2 Retatrutide Obesity Trial
Dosing studied in trials
Weekly subcutaneous injection with gradual escalation:
* 1 mg
* 2 mg
* 4 mg
* 8 mg
* 12 mg
The 12 mg weekly dose has generally produced the greatest weight loss.
Renal impairment
Based on available clinical pharmacology data, no dose adjustment is expected to be required for renal impairment, including severe CKD, but final prescribing recommendations will depend on regulatory approval and product labeling.
Common adverse effects
Similar to other incretin therapies:
* Nausea
* Vomiting
* Diarrhea
* Constipation
* Abdominal pain
* Decreased appetite
Potential future BMI indication
If approved for obesity, experts expect criteria similar to other anti-obesity medications:
* BMI ≥30 kg/m², or
* BMI ≥27 kg/m² with at least one weight-related comorbidity
However, official indications will depend on the final approved labeling.
