Peptide comparison
Retatrutide vs Tirzepatide
Retatrutide and Tirzepatide 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 | Tirzepatide | |
|---|---|---|
| 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. | Dual GIP/GLP-1 receptor agonist with strong human trial evidence for type 2 diabetes glycemic control and weight 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. | Tirzepatide is an acylated single-molecule peptide that simultaneously agonizes the GIP and GLP-1 receptors. GLP-1 receptor activation enhances glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite via central pathways. Adding GIP agonism is thought to further augment glucose-dependent insulin response and may improve lipid handling and the tolerability/efficacy balance, producing effects on appetite and energy intake that, in trials, exceeded GLP-1 monotherapy. The net clinical result is improved glycemic control and substantial caloric-intake-driven weight loss. The relative contribution of GIP versus GLP-1 signaling in humans is still an active research question. |
| Half-life | ~6 days (supports once-weekly dosing; steady state in ~4-5 weeks) | ~5 days |
| 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. | Approved once-weekly subcutaneous dosing per prescribing labels: initiate at 2.5 mg once weekly for 4 weeks (a non-therapeutic initiation dose for tolerability), then increase to 5 mg; titrate in 2.5 mg increments no sooner than every 4 weeks as needed/tolerated. Approved maintenance/maximum doses are 5, 10, or 15 mg once weekly. The ~5-day half-life supports once-weekly administration with steady state reached around 4 weeks. Dosing should be individualized and supervised by a qualified clinician. |
| Routes | subcutaneous | subcutaneous |
| 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 adverse effects are gastrointestinal: nausea (~24-33% by dose in SURMOUNT-1), diarrhea, constipation, vomiting, and decreased appetite, generally mild-to-moderate, dose-escalation-related, and often transient; discontinuation for GI effects was relatively uncommon. Gallbladder/biliary events were slightly more frequent than placebo (e.g., ~1.1% vs ~0.4% in SURMOUNT-1), partly attributable to rapid weight loss. Meta-analysis did not show a statistically significant increase in pancreatitis versus controls, though acute pancreatitis remains a labeled caution. Rare but serious risks include severe hypersensitivity/anaphylaxis; a boxed warning addresses thyroid C-cell tumors seen in rodents (human relevance unknown) and it is contraindicated with personal/family history of medullary thyroid carcinoma or MEN 2. Hypoglycemia risk rises when combined with insulin or sulfonylureas. Not recommended in pregnancy; may reduce efficacy of oral contraceptives around dose changes due to delayed gastric emptying. Use only under medical supervision. |
For research use only. Not for human consumption. Always verify against current literature.