Doses studied
Retatrutide dosage: what the trials measured, and what that means
Trial doses, pharmacokinetics, and route of administration — from the published clinical literature. This is a research digest, not a dosing guide.
What the dosing literature tells us
Retatrutide has not been approved by any regulator and has no approved dosing schedule. All numbers on this page come from clinical trials — specific doses administered by trained research staff under controlled conditions, with sterility confirmation, dose accuracy, and medical monitoring. None of these figures constitute a recommendation, a target, or a guide for non-clinical use.
The practical reason for reading trial dosing data: understanding what doses produced what outcomes in what populations, and what the side-effect profile looked like at each level, is the content of the published retatrutide record. It is also the basis for understanding what the ongoing Phase 3 TRIUMPH trials are testing. Retatrutide is administered as a once-weekly subcutaneous (injected into the fatty layer just beneath the skin) injection in all completed trials.
Retatrutide dosage
Phase 1b (first-in-human) doses studied: 0.5, 1.5, 3, and escalating sequences up to 12 mg, all once weekly over 12 weeks in adults with type 2 diabetes [4].
Phase 2 obesity trial doses studied: 1, 4, 8, and 12 mg, all once weekly, subcutaneous, over 48 weeks, in adults with obesity [1]. A dose-escalation schedule was used to improve GI tolerability — participants did not start at the full target dose but stepped up over the initial weeks.
Phase 2 type 2 diabetes trial doses studied: 0.5 to 12 mg once weekly with stepwise escalation over 36 weeks [2].
The dose-response relationship was consistent and clear in Phase 2: larger doses produced larger weight reductions, with the 12 mg group showing the largest effects in both the obesity trial (−24.2% body weight at 48 weeks) and the diabetes trial (−16.94% at 36 weeks) [1][2]. GI adverse events were also dose-dependent and were the principal driver of discontinuation at the highest dose.
The Phase 3 TRIUMPH program is studying doses that have not yet been publicly specified in the trial registry descriptions.
Half-life and pharmacokinetics
Retatrutide has an approximately 6-day half-life in humans, established in the Phase 1b trial [4]. This is the pharmacokinetic basis for once-weekly dosing: with a 6-day half-life, the compound is still present at meaningful concentrations when the next weekly injection is given, producing relatively steady exposure between doses.
Retatrutide is a 39-amino-acid peptide with a C20 fatty-diacid acylation that enables albumin binding — albumin (a carrier protein in blood) acts as a depot that releases the peptide slowly, extending its half-life far beyond what the unmodified peptide would achieve. This is the same general acylation strategy used in other long-acting incretin peptides.
Half-life is a study-design fact that explains why once-weekly administration was selected in all trials. It is not a dosing instruction.
Route of administration
All completed retatrutide trials used subcutaneous injection once weekly as the route of administration. No oral, intravenous, or nasal formulations have been reported in clinical trials. Subcutaneous injection means the compound is delivered into the fatty tissue layer beneath the skin, typically in the abdomen, thigh, or upper arm, using a fine-gauge needle.
Retatrutide delays gastric emptying [11], which is one of the mechanisms behind both its appetite-suppression effect and its GI side-effect profile (slowed gastric emptying is the physiological basis for nausea and fullness with this class of agents).
How to reconstitute retatrutide
This section addresses a frequently searched question. The direct answer: there is no approved reconstitution protocol for retatrutide. The compound has never been approved and has no FDA label. In clinical trials, it was administered as a pharmaceutical-grade formulated injection prepared by the trial sponsor under Good Manufacturing Practice (GMP) conditions — participants did not reconstitute it themselves.
Gray-market retatrutide sold in lyophilized (freeze-dried) form for research purposes is not the same as the trial compound. The Eli Lilly Phase 2 and Phase 3 material is a formulated, tested, sterile product. A lyophilized powder from a research vendor is an unverified substance of unknown purity, concentration, and sterility.
This site does not provide reconstitution instructions because doing so would be providing guidance for non-clinical use of an unapproved, unverified compound — outside any of the conditions under which the safety data summarized on this site were generated. The relevant stability notes from the trial literature: retatrutide was studied only as a clinical-trial investigational product administered by once-weekly subcutaneous injection; no approved formulation, storage, or reconstitution standard exists for any non-trial preparation.
Retatrutide availability
Retatrutide is not commercially available. It has not been approved by the FDA or any other regulatory agency. It is available only within the context of active clinical trials.
A gray market exists for retatrutide sold under a "research purposes" label. The FDA issued over 50 warning letters to retatrutide vendors in 2025 citing Federal FD&C Act violations. This site does not link to, endorse, or describe vendors. The safety and efficacy data on this site were all generated in the context of clinical trials with confirmed, GMP-grade material — not in the context of gray-market compounds.
When will retatrutide be available? If the TRIUMPH Phase 3 program meets its endpoints and Eli Lilly files for regulatory approval, and if the FDA approves the application, retatrutide could potentially become available as a prescription medicine. No timeline for approval exists as of mid-2026, and approval is not guaranteed.