How it works
Retatrutide adds glucagon receptor agonism to the GIP and GLP-1 pair that tirzepatide already covers. Glucagon agonism is expected to raise energy expenditure rather than only suppress intake, which is the mechanistic argument for why the phase 2 numbers came in higher.
It is also the part that needs the most watching. Glucagon signalling affects hepatic glucose output and heart rate, so the questions phase 3 has to answer are not only about how much weight comes off.
What the evidence shows
Mean body weight fell about 24% on the 12 mg dose against roughly 2% on placebo. No approved agent has reported a figure at that level.
Results were not available at the last review of this page. Until they read out, everything known about retatrutide rests on a single mid-stage trial.
One phase 2 trial is a signal, not a conclusion. Effect sizes routinely shrink between phase 2 and phase 3, safety findings that matter often appear only at phase 3 scale, and there is no long-term or outcomes data of any kind.
Typical dosing
There is no approved dosing schedule. The phase 2 trial escalated participants to 1, 4, 8 or 12 mg weekly under trial supervision.
Reported side effects
Rates are from the phase 2 trial, which followed 338 adults for 48 weeks across dose levels from 1 mg to 12 mg. The ranges are very wide because frequency rose sharply with dose, and the upper end of each range reflects the 12 mg group. Note that 70% of the placebo group also reported an adverse event, which is a reminder of how much gets reported in any trial. Starting at 2 mg rather than 4 mg reduced gastrointestinal effects. A dose-dependent increase in heart rate was also observed and remains unresolved. These are phase 2 figures in a small group and should be expected to change when phase 3 reports.
Labelled warnings and contraindications
- There is no approved label, so there is no labelled warning set. That is a statement about the state of the evidence, not a clean bill of health.
- The rodent thyroid C-cell signal is a class-wide consideration and has not been excluded for retatrutide.
- Dose-dependent heart rate increases were seen in phase 2 and are unresolved.
Legal status and sourcing
Retatrutide cannot legally be prescribed in the United States. It is an investigational compound and the only lawful way to receive it is enrolment in a clinical trial.
Everything sold online as retatrutide is research-use material. It is not manufactured, tested or labelled for human use, its identity and purity are unverified, and there is no clinician, no pharmacy and no recourse attached to it. Of everything in this library, this is the compound where the gap between the published science and what is actually being bought is widest.
What it costs
Not commercially available. Any price you are quoted is for unregulated research-use material.
How confident anyone can be
Low, and the enthusiasm around it is running well ahead of that. One phase 2 trial in 338 people, no phase 3 results, no long-term safety, no outcomes data.
The honest position is that retatrutide looks genuinely promising and nobody yet knows whether it is safe to take for years. Both halves of that sentence matter.