Retatrutide Dosage: What the Clinical Trials Have Administered and Measured

The numbers, plainly

Retatrutide is not an approved drug, so it has no approved dose. What this page summarizes is what doses were studied in the clinical trials — as factual, study-attributed information, not as guidance for any individual.

In the largest Phase 2 trial (48 weeks, obesity), the dose range studied was 1, 4, 8, or 12 mg injected once weekly under the skin. The highest dose — 12 mg — produced the largest weight reduction (mean -24.2%) but also the most GI side effects and discontinuations ^[1]. Earlier Phase 1b work used doses from 0.5 mg to a stepwise 3/6/9/12 mg schedule over 12 weeks in people with type 2 diabetes ^[4].

The compound's half-life — the time for blood levels to drop by half — is approximately 6 days, which is why once-weekly injection was chosen for all trials ^[4]. That is the pharmacokinetic (drug-concentration-over-time) foundation of the dosing schedule, not a starting point for personal use.

This site does not provide reconstitution instructions, dosing advice, or preparation guidance. Retatrutide is investigational; obtaining it outside a trial carries uncharacterized risks.

Retatrutide dosage — trial dose ranges by study

Phase 1b (Urva 2022, Lancet ^[4]). First-in-human multiple-ascending-dose study in 72 adults with type 2 diabetes. Doses administered: 0.5, 1.5, 3 mg fixed once weekly, plus 3/6 and 3/6/9/12 mg stepwise escalating cohorts over 12 weeks. Placebo-adjusted weight loss at the highest escalating group was -8.96 kg. Half-life approximately 6 days. This study established the pharmacokinetics that justified the once-weekly schedule across all subsequent trials.

Phase 2 obesity (Jastreboff 2023, NEJM ^[1]). 338 adults, doses of 1, 4, 8, 12 mg once weekly subcutaneous, 48 weeks. The 12 mg arm: mean body-weight change -24.2% vs -2.1% placebo. GI adverse events occurred in a dose-dependent pattern; dose escalation (gradually stepping up over the initial weeks) was used to improve tolerability. Dose escalation protocols in clinical trials are carefully controlled and monitored — the published protocols cannot be replicated without clinical oversight.

Phase 2 type 2 diabetes (Rosenstock 2023, Lancet ^[2]). 281 adults, doses 0.5-12 mg once weekly with stepwise escalation over 36 weeks. The 12 mg group achieved HbA1c -2.02% and body-weight -16.94% vs placebo. Participants on background insulin required insulin dose reductions — a medically supervised intervention that cannot be replicated without monitoring.

Phase 3 TRIUMPH program. Subcutaneous once-weekly dosing. Specific Phase 3 dose ranges had not been published in final form as of mid-2026. TRIUMPH-2 (NCT05931367), the cardiovascular outcomes trial (NCT06383390), and the head-to-head trial vs tirzepatide (NCT06662383) are ongoing ^[7][8][9].

Retatrutide half life and pharmacokinetics

Retatrutide's half-life is approximately 6 days in human plasma, established in the Phase 1b trial ^[4]. This is achieved by the C20 fatty-diacid acylation (a long fatty-acid chain attached to the molecule) that binds the peptide to serum albumin (the most abundant protein in blood), dramatically slowing elimination compared to short-acting peptides.

The ~6-day half-life has two practical implications in trial design. First, it supports once-weekly subcutaneous dosing without the need for daily injection. Second, after stopping administration, the compound remains in the system for approximately 4-5 weeks before falling to negligible levels — relevant both for trial wash-out periods and for understanding the persistence of any side effects after cessation.

In comparison, native GLP-1 has a plasma half-life of approximately 1-2 minutes; GLP-1 receptor agonist drugs engineered for weekly dosing range from approximately 5 days (semaglutide) to approximately 6 days (retatrutide). The relatively similar pharmacokinetics to semaglutide but the significantly greater weight-loss magnitude in Phase 2 is one of the pharmacodynamically interesting observations in the 2025 review literature ^[6].

How to reconstitute retatrutide — and why this page cannot tell you

How to reconstitute retatrutide is among the most searched questions about this compound. The answer has two parts.

First, the factual context: in clinical trials, retatrutide was administered as a ready-made solution (a pre-filled syringe or vial formulated for clinical use by Eli Lilly), not as a lyophilized powder (freeze-dried material) requiring reconstitution by the end user. No approved formulation exists. No FDA-cleared package insert specifying reconstitution instructions, solvent concentration, storage conditions, or sterility requirements has been published for retatrutide.

Second, the reason this page provides no preparation guidance: research-labeled retatrutide sold through gray-market channels is an unregulated, unverified substance. It may or may not contain what the label states, at what concentration, with what impurities, and with what sterility characteristics. Providing reconstitution numbers for an unapproved compound without verified identity, purity, or sterility data would be providing instructions for an unknown substance — which is not what this site does.

For storage, the clinical trial protocols stored the investigational product under conditions specified by the sponsor, not disclosed in the published papers. Any temperature or storage recommendation for gray-market material is speculation without the validated stability data that a licensed formulation would require.

For questions about how to participate in an active retatrutide clinical trial, ClinicalTrials.gov lists the TRIUMPH program trials with eligibility and enrollment information.

Retatrutide cost — an unapproved compound has no list price

Retatrutide cost as a prescription medicine cannot be stated because retatrutide is not a prescription medicine — it has no approved labeling, no list price, and no insurer coverage. What exists in the market are gray-market research-labeled materials at prices set by unregulated vendors; those prices vary widely, are not correlated with verified product quality, and are not reported on this site.

For reference context: approved GLP-1 receptor agonists for obesity in the United States have list prices in the range of $900-$1,400 per month before insurance, with actual patient cost varying substantially based on coverage and manufacturer assistance programs. What a potential approved retatrutide would cost is unknown — it would depend on FDA approval, Eli Lilly's pricing decisions, and payor coverage frameworks that do not yet exist. Published commentary on the obesity pharmacology market has noted that the high Phase 2 efficacy figures may lead to pricing above existing approved agents if Phase 3 trials confirm those results.