Retatrutide Dosage: What Phase 1 and Phase 2 Trials Administered

Retatrutide in clinical trials — what this page covers

Retatrutide (LY3437943) is an investigational drug. It has no approved dosing regimen because it is not approved anywhere. The information here describes the dose levels, routes, and escalation schedules used in published Phase 1 and Phase 2 trials — study-design facts, not guidance for any person.

This page is a record of what was measured in controlled trials, not instructions on how to use retatrutide. Retatrutide is not available as a prescription product. Gray-market research-labeled material is unregulated and of unverified identity and purity. The trial doses below were administered to participants under continuous medical supervision with verified pharmaceutical-grade material.

For the drug's mechanism — how it works at the receptor level — see how does retatrutide work. For half-life and PK data in detail, see the retatrutide half life page.

Retatrutide dosage in Phase 2 obesity trials

Phase 2 obesity trial (Jastreboff et al., NEJM, 2023). Doses studied: 1 mg, 4 mg, 8 mg, and 12 mg, administered as once-weekly subcutaneous injections for 48 weeks. Dose escalation was used: participants stepped up from lower to higher doses over the first weeks of the trial to allow GI tolerability to develop ^[1].

Phase 2 type 2 diabetes trial (Rosenstock et al., Lancet, 2023). Doses studied: 0.5 mg, 3 mg, 6 mg, 9 mg, and 12 mg, once weekly with stepwise escalation; escalation rate was a pre-specified variable in this trial, comparing faster and slower up-titration to characterize the dose-escalation-rate/tolerability relationship ^[2].

Phase 1b first-in-human PK study (Urva et al., Lancet, 2022). Dose groups: 0.5 mg, 1.5 mg, 3 mg, 3/6 mg, and 3/6/9/12 mg (multi-ascending dose within a group); once-weekly subcutaneous over 12 weeks. Established the half-life (~6 days) and initial safety/tolerability profile ^[4].

All doses in the above trials: subcutaneous (injected into the fatty layer beneath the skin), once weekly. No intravenous, intramuscular, or oral formulation has been studied in published trials.

Retatrutide dosage — escalation strategy

Dose escalation is a standard practice in GLP-1-class trials: starting at a low dose and incrementing over weeks gives the GI tract time to adapt to slowed gastric motility, reducing nausea and vomiting rates. The 2025 pipeline review by Madsbad et al. (Expert Opinion on Investigational Drugs) identified slow up-titration as the key strategy for managing GI adverse-event burden across the incretin class ^[12].

In the Phase 2 obesity trial, the 18% discontinuation rate at 12 mg was principally GI-driven ^[1]. In the type 2 diabetes trial, a lower escalation rate was associated with improved tolerability ^[2]. The 2026 comprehensive overview (Panou et al.) linked GI event rates directly to escalation rate and starting dose ^[15].

No approved escalation schedule exists for retatrutide because the drug is not approved. The schedules described above are trial protocols, not instructions.

How to reconstitute retatrutide

No approved formulation, storage specification, or reconstitution standard exists for retatrutide outside clinical trials.

In clinical trials, retatrutide was administered as a pharmaceutical-grade investigational product prepared and dispensed by clinical pharmacies under Good Manufacturing Practice (GMP) conditions with verified identity, potency, sterility, and endotoxin testing. Trial participants did not reconstitute the compound themselves — they received pre-prepared injections administered under clinical oversight.

Gray-market 'research-labeled' retatrutide is not pharmaceutical grade. There is no validated reconstitution protocol for non-trial material because no such material has been through the pharmaceutical development process that generates one. Any 'reconstitution recipe' circulating in research communities reflects improvised practice, not a validated standard.

The FDA issued warning letters to gray-market retatrutide vendors in 2025. This site does not provide reconstitution instructions and does not link to vendors.

Retatrutide availability

Retatrutide is not available through any legitimate pharmacy or physician as of 2026. It has no approved indication, no NDA (New Drug Application) approval, and no compassionate use or expanded access program listed on ClinicalTrials.gov as of the time of this writing.

The only legitimate access route is enrollment in an active TRIUMPH Phase 3 clinical trial. Trial eligibility criteria, site locations, and enrollment status are listed at ClinicalTrials.gov (search 'LY3437943' or 'retatrutide').

The gray market for research-labeled retatrutide exists but is unregulated. The FDA has cited vendors for Federal FD&C Act violations. Material sold through these channels cannot be confirmed to contain authentic retatrutide at stated concentration.

When will retatrutide be available

Retatrutide's regulatory timeline is not publicly announced by Eli Lilly. Phase 3 trials (TRIUMPH) are ongoing as of mid-2026. The regulatory review process after trial completion typically takes 12–24 months. No FDA filing date has been publicly stated.

A 2025 systematic review (Kokkorakis et al., Pharmacological Reviews) identified retatrutide among 14 agents in active Phase 3 programs, characterizing the incretin-analog category as the most promising in the pipeline and noting that long-term follow-up on cardio-renal-metabolic outcomes is required before the full benefit-risk picture is established ^[11].

Regulatory approval cannot be assumed or predicted from Phase 2 results. Phase 3 trials may produce unexpected safety signals or fail to meet primary endpoints.

Retatrutide cost

Retatrutide has no approved commercial price. It is not sold through pharmacies, insurance formularies, or any authorized distribution channel. Cost projections before regulatory approval are speculative.

Analysts have noted that the incretin-class drugs already approved for obesity and diabetes carry high list prices in the United States, with significant variation by formulary tier and insurance coverage. Whether retatrutide would be priced similarly, competitively lower, or higher — and what its coverage landscape would look like — will only be known following regulatory approval and launch.

This site does not track or estimate retatrutide pricing. No purchase information or vendor links are provided.