Retatrutide Dosage: What the Clinical Trials Studied

The short version

Retatrutide is an investigational drug — nothing here is a guide for taking it. This page reports what amounts were used in clinical trials, how they were given, and what the pharmacokinetics (how the body handles the drug over time) looked like. In the main Phase 2 trial, amounts ranged from 1 to 12 mg by injection once a week. In the first human study, researchers measured a half-life of about 6 days, which is why once-weekly dosing was chosen. The trials also used a step-up approach — starting low and gradually increasing — to reduce nausea. These are study-design facts, not instructions.

Retatrutide dosage in Phase 2 trials

In the 48-week Phase 2 obesity RCT, participants received subcutaneous (injected into the fatty tissue just under the skin) retatrutide at 1, 4, 8 or 12 mg once weekly. Dosing was fixed-dose after initial titration; the protocol used a gradual ramp-up to the target dose to manage GI tolerability ^[1].

In the 36-week Phase 2 type 2 diabetes RCT, doses ranged from 0.5 to 12 mg once weekly with stepwise escalation — a protocol in which participants start at the lowest amount and incrementally increase over several weeks — consistent with the approach used for other incretin-class agents to reduce nausea and vomiting during the early weeks of treatment ^[2].

The Phase 1b first-in-human trial tested 0.5, 1.5, 3, 3/6, and 3/6/9/12 mg once weekly (the last two arms used multi-step escalation within the 12-week study period) ^[4]. The MASLD substudy used the same four-arm design as the obesity trial (1, 4, 8, 12 mg) ^[5].

Half-life and pharmacokinetics

Retatrutide has an approximately 6-day half-life in humans, established in the Phase 1b study ^[4]. Half-life is the time for blood concentration to fall by half — a 6-day half-life supports once-weekly subcutaneous dosing because meaningful concentrations persist between weekly administrations.

The extended half-life is engineered into the molecule: a C20 fatty-diacid acyl chain binds retatrutide reversibly to albumin (a carrier protein circulating in the blood), slowing its clearance through the kidneys and extending how long it remains active.

In the Phase 1b study, the placebo-adjusted weight change over 12 weeks at the highest-tested escalation reached -8.96 kg (90% CI -11.16 to -6.75 kg) ^[4]. Treatment-emergent adverse events (TEAEs — side effects that emerge or worsen during treatment) occurred in 63% of participants; most were GI and categorized as mild to moderate.

Route of administration

All published clinical trials have administered retatrutide via subcutaneous injection (SC) once weekly. No oral, intravenous, or other route has been studied. Retatrutide is a 39-amino-acid peptide and, like all peptides of this size, would be degraded by digestive enzymes if taken orally without specialized formulation.

No approved formulation for retatrutide exists. Research-labeled material available outside trials lacks any verified standard for storage, reconstitution, or sterile preparation. Stability data for non-clinical-trial preparations have not been published.

How to reconstitute retatrutide — context on the question

This is one of the most-searched questions about retatrutide. The answer requires context: no approved formulation exists. In the Phase 3 clinical trials, retatrutide is supplied as a pre-formulated, sterile, GMP-manufactured solution administered by healthcare staff or by participants trained in self-injection under clinical oversight. There is no published reconstitution standard for any non-trial preparation because none is approved.

Research-labeled lyophilized (freeze-dried) retatrutide sold outside clinical trials is not the same as trial drug. The compound's 39-amino-acid structure with a long fatty-acid chain is susceptible to aggregation, degradation, and contamination if not handled under controlled conditions. This site does not provide reconstitution instructions for non-clinical materials, and doing so would misrepresent the state of the science.

Retatrutide cost — what is known from the research context

No approved price for retatrutide exists — it has not been approved and is not commercially sold. Pricing for any research-labeled gray-market material is entirely unregulated and carries no quality guarantee. For comparison, GLP-1-class approved agents in the same therapeutic area have launched in the US at list prices roughly in the $1,000-$1,500/month range before rebates, but retatrutide pricing will depend on Eli Lilly's eventual pricing strategy upon approval, which has not been announced.