Retatrutide is an investigational drug with no approved label and no established dose anywhere in the world. The numbers on this page describe how published clinical trials were designed, so readers can understand the research. They are not instructions, and no product sold as "retatrutide" is a verified pharmaceutical.
Overview
There is no approved retatrutide dose — the only doses that exist are the ones its clinical trials were built around. In those trials, retatrutide was given as a once-weekly subcutaneous injection, started at 2–4 mg, and escalated stepwise to randomized maintenance doses between 1 and 12 mg (Jastreboff et al., NEJM 2023). Understanding that structure explains most of what people ask about "retatrutide dosing": why the numbers people quote range so widely, why escalation is slow, and why none of it translates into a real-world regimen.
How the phase 2 trials were designed
The phase 2 obesity trial (n=338, 48 weeks) randomized participants across a deliberately wide dose range to map the dose–response curve (NEJM 2023):
- Route and frequency: subcutaneous injection once weekly.
- Initial doses: 2 mg or 4 mg weekly, depending on the assigned arm.
- Maintenance doses studied: 1, 4, 8, and 12 mg weekly, reached by stepwise escalation.
- Outcome by dose: mean weight change ran from −8.7% at 1 mg to −24.2% at 12 mg over 48 weeks, so effect size tracked dose — and so did gastrointestinal side effects.
The phase 2 type 2 diabetes trial (n=281) tested an even wider spread — seven maintenance doses from 0.5 mg to 12 mg over 36 weeks — against placebo and dulaglutide (Rosenstock et al., The Lancet 2023). Dose-ranging like this is how sponsors decide what to carry into phase 3; it is not a menu.
What phase 3 changed
Phase 3 narrowed the field. TRANSCEND-T2D-1, the first published phase 3 trial (n=537, type 2 diabetes, 40 weeks), evaluated maintenance doses of 4, 9, and 12 mg weekly (Bajaj et al., The Lancet 2026) — note the 9 mg step, which did not exist in phase 2. The pivotal TRIUMPH obesity trials use their own protocol-defined escalation schedules (TRIUMPH-1, NCT05929066). Which dose, if any, ends up on an approved label is a regulatory decision that has not been made.
Why trials escalate the dose
Every trial in the program starts low and steps up rather than beginning at the maintenance dose. The reason is tolerability: nausea, vomiting, and other GI effects are dose-related, and in the phase 3 diabetes trial they were concentrated early and subsided over time (The Lancet 2026). Slow escalation is also paired with monitoring that has no self-directed equivalent — heart rate in particular, since retatrutide's glucagon-receptor arm produced a heart-rate increase that peaked around week 24 in phase 2 (NEJM 2023). The same escalation logic appears on the labels of approved relatives like tirzepatide — but there, a regulator has reviewed the schedule and a clinician adjusts it per patient.
Why there is no real-world dose
Outside a trial, none of the machinery that makes those numbers meaningful exists:
- No verified product. Retatrutide is supplied only to trial sites. Vials sold online are unapproved products of unverified identity, concentration, and sterility — the FDA has warned about unapproved GLP-1 class drugs sold for weight loss (FDA).
- No label. Trial doses assume trial oversight — screening, exclusion criteria, scheduled monitoring, and stopping rules.
- Reconstitution risk. Gray-market powder must be reconstituted and measured in syringe units; a concentration error silently multiplies the dose of a drug whose ceiling effects are still being studied.
The dosing story worth knowing is the trial design itself — what was tested, why it was escalated, and what remains undecided. For what those trials found, see the research-evidence page and the side-effects page.