Searches for a retatrutide dosage are looking for a number, and unlike most research peptides, retatrutide does have detailed human trial data. But the essential point comes first: retatrutide is an investigational drug that is not approved by any regulator, so there is no approved dose. The amounts below are the weekly quantities assigned in registered clinical trials — study arms, not a recommendation, and not available for use outside those trials. This article documents what has actually been investigated; it is a review of published research, not dosing guidance.
What is retatrutide?
Retatrutide is an investigational, once-weekly triple hormone-receptor agonist that activates the GIP, GLP-1 and glucagon receptors. It is being developed by Eli Lilly (development code LY3437943) and studied primarily for obesity, type 2 diabetes and metabolic dysfunction-associated steatotic liver disease (MASLD/MASH). As of this review it remains investigational, with Phase 3 trials ongoing and no marketing approval anywhere.
Is there an established retatrutide dosage?
No — there is no approved retatrutide dose, because the drug is not approved. What exists are investigational trial protocols: fixed weekly amounts assigned in Phase 2 studies, usually reached through a gradual escalation. An investigational trial protocol is not the same as an approved dosing regimen, and it does not become a recommendation by being published. The next sections document those trial amounts as historical study design.
Retatrutide dosage investigated in human clinical research
| Study | Participants | Quantity investigated | Frequency | Route | Duration | Primary focus |
|---|---|---|---|---|---|---|
| Phase 2 obesity, Jastreboff et al., NEJM 2023 (NCT04881760) | 338 adults with obesity/overweight | 1, 4, 8 or 12 mg vs placebo | Once weekly | Subcutaneous | 48 weeks | Percentage change in body weight |
| Phase 2 type 2 diabetes, Rosenstock et al., Lancet 2023 | Adults with type 2 diabetes | Up to 12 mg across several arms | Once weekly | Subcutaneous | 36 weeks | Change in HbA1c and body weight |
| Phase 2a MASLD, Sanyal et al., Nature Medicine 2024 | Adults with MASLD | Weekly retatrutide arms | Once weekly | Subcutaneous | Multi-week | Liver-fat change |
The most detailed dataset is the Phase 2 obesity trial (Jastreboff et al., NEJM 2023). It randomised 338 adults to once-weekly subcutaneous retatrutide at 1, 4, 8 or 12 mg or placebo for 48 weeks. Parallel Phase 2 programmes evaluated retatrutide in type 2 diabetes (Rosenstock et al., Lancet 2023) and in fatty-liver disease (Sanyal et al., Nature Medicine 2024). All used the once-weekly subcutaneous route.
Dose-escalation research
The Phase 2 obesity trial was designed with gradual dose escalation rather than starting participants at the target amount. Higher target groups began at a lower weekly amount (for example an initial 2 mg or 4 mg step) and were stepped up over several weeks toward the assigned target (8 mg or 12 mg). This escalation is a trial-design feature intended to improve tolerability under medical supervision — it describes how investigators structured the study, and is not an instruction or protocol for personal use.
Preclinical (animal and laboratory) research
Retatrutide's mechanism was characterised in preclinical pharmacology (receptor-activity studies and animal metabolic models) before human trials. Because the compound advanced rapidly into large human studies, the publicly prominent quantitative data is clinical rather than preclinical. As with any compound, animal amounts are dosed by body weight and cannot be interpreted as an equivalent human dosage.
What did different dosage groups show?
The obesity trial showed a clear dose–response relationship. At 48 weeks, the least-squares mean change in body weight was approximately -8.7% (1 mg), -17.1% (4 mg), -22.8% (8 mg) and -24.2% (12 mg), compared with about -2.1% for placebo. At the earlier 24-week point the corresponding figures were roughly -7.2%, -12.9%, -17.3% and -17.5% versus -1.6% placebo. In other words, larger weekly amounts were associated with greater average weight reduction, but — as the next section notes — also with more gastrointestinal side effects. These are trial outcomes, reported historically; they are not a basis for choosing an amount.
Safety and adverse events reported in research
The most common adverse events were gastrointestinal — nausea, vomiting and diarrhoea — consistent with the incretin (GIP/GLP-1) drug class, and they were generally dose-related, occurring more often in the higher-amount groups. Trials of this class also monitor heart rate and glucose-related effects. Because retatrutide is investigational, its complete long-term safety profile is still being established in Phase 3. Adverse events should not be minimised: higher weekly amounts delivered more weight change but also more side effects in the reported data.
What the research does not tell us
- It does not provide an approved dose — retatrutide is investigational and unapproved everywhere.
- Phase 2 trial arms are not a licensed regimen and were given under medical supervision within trials.
- Long-term efficacy and safety are still being evaluated in Phase 3 (the TRIUMPH programme).
- Animal pharmacology amounts cannot be converted into a human dose.
Retatrutide research timeline
- 2023 — Phase 2 obesity results published in the New England Journal of Medicine (1/4/8/12 mg weekly, 48 weeks).
- 2023 — Phase 2 type 2 diabetes results published in The Lancet.
- 2024 — Phase 2a fatty-liver (MASLD) results published in Nature Medicine.
- Ongoing — Phase 3 TRIUMPH programme; no regulatory approval as of this review.
Key takeaway
Retatrutide has been investigated in humans at once-weekly subcutaneous amounts of 1, 4, 8 and 12 mg in Phase 2 trials for obesity, type 2 diabetes and fatty-liver disease, with a clear dose–response for weight change and dose-related gastrointestinal side effects. It has no approved dose and is not licensed by the MHRA, EMA or FDA. The amounts above are investigational trial arms given under medical supervision — they describe scientific research and are not a personal dosing recommendation.
References
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. 2023;389(6):514–526. DOI: 10.1056/NEJMoa2301972. Trial: NCT04881760.
- Rosenstock J, Frias J, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo- and active-controlled, parallel-group, phase 2 trial. The Lancet. 2023;402(10401):529–544. PubMed: PMID 37385280.
- Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature Medicine. 2024. PMC: PMC11271400.