Retatrutide dosage chart: phase 3 doses, units and vial math

The phase 3 program used 4-week steps, like every other weekly incretin drug. Participants started at 1 or 2 mg once weekly and moved up every 4 weeks toward a randomized maintenance arm of 4, 8 or 12 mg. The 12 mg arm is the one behind the headline figure: Lilly's 2026 TRIUMPH-1 topline reported about 28 percent average weight loss over 80 weeks at that dose, roughly 70 lb. Those are sponsor-reported topline numbers pending full publication.

The phase 2 trial, published in 2023, used the same structure and is the only peer-reviewed dosing source. At 12 mg weekly, participants lost about 24 percent of body weight at 48 weeks with the curve still falling. Dropouts in phase 2 were driven by fast escalation, which is why the phase 3 protocol and every sensible community protocol hold each step for the full 4 weeks.

The compound page gives the reported range as 1 to 12 mg per dose and notes that community users who copy the trial schedule usually hold at the lowest dose that controls appetite, most often 4 to 8 mg. Twelve mg is the trial maximum, not a target.

A label requires an approved drug, and retatrutide is still in phase 3. TRIUMPH-1, -2 and -3 have reported topline results in 2026 and met their primary endpoints, but topline means the sponsor has announced the headline numbers from a locked database, not that the full data have been reviewed. Lilly has said it plans to file for FDA approval in the first quarter of 2027. Review typically takes most of a year, so approval is not expected before late 2027 at the earliest.

Until then, the only dosing information is what the trials did, and the trials were not designed to tell an individual what dose to take. The arms were fixed by randomization. There is no equivalent of the Zepbound label's as-tolerated language, no missed-dose guidance, no maintenance dose instruction and no restart protocol. Anyone writing a retatrutide dosage schedule is extrapolating from tirzepatide and from trial design. Our phase 3 results explainer covers what has and has not been announced.

It also means the safety picture is incomplete. The phase 2 trial ran 48 weeks and the phase 3 trials 80 weeks; there are no cardiovascular outcome data and no long-term safety data. Retatrutide is on the WADA prohibited list, and the compound page rates its safety data as limited for exactly these reasons.

Units are a volume on a U-100 insulin syringe, where 1 unit is 0.01 mL, so the answer depends on the concentration. At 2 mg/mL, 1 mg is 0.5 mL, or 50 units. At 5 mg/mL it is 20 units. At 10 mg/mL it is 10 units. The live chart above runs the full ladder from 1 to 12 mg at each concentration.

The spread between steps is wide. At 10 mg/mL the trial doses are 10, 20, 40, 60, 80 and 120 units; the 12 mg step does not fit in a 1 mL syringe. At 2 mg/mL the 1 mg start is a comfortable 50 units but anything above 2 mg exceeds the syringe. Five mg/mL is the compromise most people land on for the early months: 20 units for 1 mg, 80 units for 4 mg, and 8 mg needs two draws.

Because no pharmacy dispenses retatrutide, every vial is user-reconstituted and every units figure is self-calculated. The calculator takes the vial amount and water volume and returns the units for any dose; the insulin syringe units chart explains the syringe sizes and the formula.

Retatrutide is sold almost entirely as 10, 20 and 30 mg lyophilized vials. The compound page lists 10 mg with 1 mL, 20 mg with 2 mL and 30 mg with 3 mL as standard reconstitutions, all of which give 10 mg/mL. Doubling the water (10 mg with 2 mL, 20 mg with 4 mL) gives 5 mg/mL and makes the 1 and 2 mg steps larger, easier draws.

Vial size and dose rarely line up neatly. At the 1 mg starting dose, a 10 mg vial is ten weeks of doses, well past the 4 week refrigerated window the compound page gives for reconstituted retatrutide. At 8 mg a 10 mg vial is barely one dose. People starting out tend to waste part of a vial or share one, and people at maintenance go through a 20 mg vial every two to three weeks. Buying the vial size that matches the current step is the only clean solution.

The bigger problem is that the number on the vial may not match the contents. Retatrutide's hype has attracted underdosed and mislabeled product, and the compound page says plainly that purity, concentration and even identity vary between suppliers. A units calculation built on a 10 mg label that actually contains 6 mg is wrong by 40 percent. Third-party testing of the batch, covered in how to read a COA, is the only check that exists.

Every GLP-1 drug raises resting heart rate a little. Retatrutide raises it more, by several beats per minute in the early months of treatment, and the compound page attributes that to the glucagon component. In phase 2 the increase appeared in the first weeks and drifted back toward baseline over time. The brief's summary of the 2026 phase 3 topline is that heart rate remains the extra safety signal versus tirzepatide.

This changes the dosing calculus in two ways. First, it argues for the slow 4-week ladder even more strongly than for tirzepatide, because the heart rate effect and the GI effects both build for two to three weeks after each step. Second, it makes stimulants a real interaction: the compound page flags caffeine, pre-workouts and decongestants as things that compound the effect. The compound page's stop list includes a resting heart rate that stays more than about 20 beats above baseline, or palpitations.

People with arrhythmias or uncontrolled blood pressure are flagged for caution on the compound page. Without outcomes data, nobody knows whether a sustained heart rate rise matters clinically over years. That question is what a cardiovascular outcomes trial answers, and none has been reported.

The three ladders look alike because the pharmacology is alike: weekly injection, 4-week steps, a tolerance dose at the bottom. Tirzepatide runs 2.5 to 15 mg, semaglutide 0.25 to 2.4 mg and retatrutide 1 to 12 mg. The mg figures are not comparable across compounds; a 12 mg retatrutide dose is not a bigger dose than 15 mg of tirzepatide in any meaningful sense, just a different molecule with its own potency.

What differs is the evidence behind each number. Tirzepatide's steps come from an FDA label built on multiple completed trials and years of real-world use. Semaglutide's add a cardiovascular outcomes trial. Retatrutide's come from one published phase 2 trial and sponsor topline announcements. On paper the weight loss is larger; in practice the data are thinner. The retatrutide vs tirzepatide and retatrutide vs semaglutide comparisons go through this in detail.

Stacking is not a way around the choice. The compound page lists tirzepatide and semaglutide as compounds to avoid alongside retatrutide, because the GLP-1 and GIP activity overlap and the GI effects add while the benefit does not. Someone switching from one to another is generally starting the new ladder from a low step, not matching the old mg.

The early weeks are rougher than semaglutide, according to the compound page: nausea, vomiting and diarrhea, a resting heart rate rise, and in a minority of phase 2 participants a skin tingling or heightened sensitivity (dysesthesia) that usually resolved. Each step up brings a GI flare that can keep building for two to three weeks because of the 6 day half-life. By month 3 to 6 at a stable dose, the compound page describes heart rate drifting back and side effects easing.

Stop signals are the same as the class plus the heart rate item: severe or persistent abdominal pain, vomiting that prevents keeping fluids down, a neck lump or hoarseness, skin sensations that spread rather than fade, or a resting heart rate that stays well above baseline. Assume the class pancreatitis, gallbladder and thyroid warnings apply even though there is no label to carry them. The GLP-1 side effects article covers each by step, including the January 2026 MHRA pancreatitis alert.