Peptide comparison
Retatrutide vs Semaglutide
Retatrutide and Semaglutide are both research peptides. This side-by-side compares their mechanism, typical research dosing, half-life, routes and safety so you can see how they differ. For research use only.
| Retatrutide | Semaglutide | |
|---|---|---|
| Category | Metabolic | Metabolic |
| Overview | Investigational once-weekly triple agonist (GIP/GLP-1/glucagon) by Eli Lilly; phase 2 data show large weight loss. Not approved. | GLP-1 receptor agonist with strong human-trial evidence for weight loss, glycemic control, and cardiovascular risk reduction. |
| How it works | Retatrutide is a single synthetic peptide that agonizes three incretin/metabolic receptors: GIP, GLP-1, and glucagon. GLP-1 and GIP agonism enhance glucose-dependent insulin secretion and promote satiety/slowed gastric emptying (reducing food intake), while glucagon-receptor agonism is proposed to increase energy expenditure and hepatic fat mobilization. A C20 fatty-diacid moiety promotes reversible binding to serum albumin, creating a depot effect that extends the half-life and supports once-weekly dosing. The combined appetite-suppression plus energy-expenditure mechanism is the leading hypothesis for its observed weight-loss magnitude, though the relative contribution of each receptor in humans is not fully resolved. | Semaglutide selectively activates the GLP-1 receptor, mimicking the incretin hormone GLP-1. It enhances glucose-dependent insulin secretion and suppresses glucagon release (lowering blood glucose with low intrinsic hypoglycemia risk), slows gastric emptying, and acts on appetite-regulating centers in the hindbrain and hypothalamus to increase satiety and reduce food intake. The glucose-dependent nature of its insulinotropic effect means insulin is stimulated mainly when blood glucose is elevated. Its long duration of action is driven by albumin binding and resistance to enzymatic degradation rather than by a different receptor target. |
| Half-life | ~6 days (supports once-weekly dosing; steady state in ~4-5 weeks) | ~1 week (~160 hours) |
| Dosing reference | In Eli Lilly trials, retatrutide is given as a once-weekly subcutaneous injection with stepwise dose escalation to limit GI side effects. The phase 2 obesity trial used maintenance doses of 1, 4, 8, and 12 mg weekly, titrated upward over the first ~12-16 weeks (e.g., starting around 2-4 mg and increasing every 2-4 weeks). The largest weight loss occurred at 8-12 mg. These are investigational protocols; retatrutide has no approved label or established clinical dosing for general use. | For type 2 diabetes (Ozempic), subcutaneous dosing typically starts at 0.25 mg once weekly for 4 weeks (a non-therapeutic initiation dose), increasing to 0.5 mg/week, then up to 1 mg or 2 mg/week as needed and tolerated. For chronic weight management (Wegovy), a stepwise 16-week escalation is used: 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, then a 2.4 mg/week maintenance dose. Slow titration is emphasized to limit gastrointestinal side effects; rapid escalation has been linked to severe GI complications including gastroparesis. |
| Routes | subcutaneous | subcutaneous, oral |
| Safety & side effects | The most common adverse events in trials are gastrointestinal - nausea, vomiting, diarrhea, and constipation - which are dose-dependent, mostly mild-to-moderate, and concentrated during dose escalation; a lower starting dose and slower titration reduce them. Dose-dependent increases in heart rate (roughly 5-10 bpm) have been observed. Trial discontinuations due to adverse events ranged from about 6-16% across retatrutide arms. Through 48 weeks no hepatotoxicity signal was reported in the MASLD substudy, and no ketoacidosis occurred despite mild increases in ketone markers. As a glucagon-receptor agonist, blood-glucose effects warrant monitoring, particularly with concurrent diabetes medication. Long-term safety, cardiovascular outcomes, and effects of unregulated research-grade product are unknown. Class cautions for incretin agonists include pancreatitis, gallbladder issues, and a theoretical thyroid C-cell tumor signal seen in rodents. Not for use in pregnancy. Research-use-only; not approved for human consumption. | Most common side effects are gastrointestinal: nausea, vomiting, diarrhea, constipation, and abdominal pain, usually mild-to-moderate and most pronounced during dose escalation. More serious but less common risks include acute pancreatitis, gallbladder disease (cholelithiasis/cholecystitis), and, with rapid dose escalation, gastroparesis. Hypoglycemia risk rises when combined with insulin or sulfonylureas. In rodents semaglutide caused dose-dependent thyroid C-cell tumors; human relevance is considered low, but it is contraindicated in those with personal/family history of medullary thyroid carcinoma or MEN 2, and in pregnancy. Worsening diabetic retinopathy was noted in SUSTAIN-6. Rapid weight loss may contribute to lean-mass loss. Use only under medical supervision; gray-market product carries purity and dosing-accuracy risks. |
For research use only. Not for human consumption. Always verify against current literature.