Retatrutide adds a third receptor, glucagon, to tirzepatide's two. Phase 2 weight loss looks larger than anything tirzepatide has reported, but the two have never been compared directly and retatrutide has no completed Phase 3.
Side by side
| Retatrutide | Tirzepatide | |
|---|---|---|
| Class | GLP-1 / GIP / glucagon triple agonist | GLP-1 / GIP dual agonist |
| Status | Phase 3 investigational | FDA approved |
| Route | Subcutaneous injection | Subcutaneous injection |
| Typical vials | 5 mg, 10 mg, 15 mg, 30 mg | 5 mg, 10 mg, 15 mg, 30 mg, 60 mg |
| Dose range | 2 mg to 12 mg | 2.5 mg to 15 mg |
| Frequency | Once weekly | Once weekly |
| Half-life | ~6 days | ~5 days |
| Dosing unit | milligrams | milligrams |
Pharmacokinetics
What the evidence supports
These grade how well each outcome has been studied in humans, never how well either compound works. A strong grade can sit on a negative result.
Both top out at the same tier of evidence: Human RCT. Where they differ is in which outcomes have been asked about, not in how well either has been studied overall.
Retatrutide
| Outcome | Evidence |
|---|---|
| Glycemic control | Human RCT |
| Hepatic steatosis / MASLD | Human RCT |
| Weight loss | Human RCT |
| Long-term safety | No data |
Tirzepatide
| Outcome | Evidence |
|---|---|
| Cardiovascular event reduction | Human RCT |
| Glycemic control in type 2 diabetes | Human RCT |
| Obstructive sleep apnea severity | Human RCT |
| Weight loss | Human RCT |
| Lean mass preservation | Human, observational |
How to choose
Tirzepatide is the known quantity
Approved, with completed Phase 3 trials, published safety data over years, and a defined manufacturing source.
Retatrutide's advantage is a cross-trial impression
Comparing a Phase 2 result against a different drug's Phase 3 is the least reliable form of comparison there is. Phase 2 populations are smaller and selected differently.
The glucagon arm is the open question
It is the mechanistic reason to expect more effect, and also the reason to watch hepatic and heart-rate signals until larger trials report.
Retatrutide is not available as an approved product
Anything obtained now is research-grade, so the trial evidence describes a molecule, not the vial in hand.
At the syringe
At the default setup on each compound's own page, a 10 mg vial in 2 mL puts 50 mcg on every insulin unit, while a 10 mg vial in 2 mL puts 50 mcg on every unit. That is the number that decides whether a dose lands on a readable mark, and it is set by how much water goes in, not by the compound.