The Complete Retatrutide Dosage Guide 2026: Dosing Chart in Units

What is retatrutide?

Retatrutide (LY3437943) is Eli Lilly’s once-weekly peptide that activates three receptors at once: GIP, GLP-1 and glucagon. Semaglutide acts on GLP-1 alone and tirzepatide on GIP and GLP-1. The glucagon receptor is the addition, studied for raising energy expenditure and clearing liver fat. A fatty-acid chain binds retatrutide to albumin in the blood, which gives it a half-life of about six days and makes one injection a week enough.

Every retatrutide dose with published results comes from Lilly’s trials, chiefly a 12-week Phase 1b study, two Phase 2 trials published in 2023, and four Phase 3 TRIUMPH trials with results released through July 2026. In all of them retatrutide was injected under the skin once a week, at 0.5 to 12mg, starting low and stepping up every four weeks. Simms Research sells it as Retatrutide (GLP-3) in 10mg, 20mg, 30mg and 60mg vials.

This guide covers the schedules the trials used, how many units each dose is on an insulin syringe, how long each vial size lasts, what each dose produced, and the practical questions the trials leave open: splitting the dose, missed doses and switching from tirzepatide.

Retatrutide dosing schedule and dosage chart

Every Phase 3 participant started at 2mg once a week and moved up one step every four weeks until reaching an assigned dose of 4, 9 or 12mg. The steps were 2, 4, 6, 9 and 12mg. The Phase 2 obesity trial used a shorter ladder, 2, 4, 8 and 12mg, and reached 12mg four weeks sooner.

Participants assigned to 4mg stayed there from week 5, and those assigned to 9mg from week 13. The four-week spacing follows the drug itself: with a six-day half-life, levels take about four weeks of weekly injections to settle, so each step lasts about as long as the body needs to reach a steady level at that dose. The trials moved everyone on a fixed calendar, but four weeks is a minimum between increases, the way tirzepatide’s label puts it, not a deadline.

Two other schedules circulate as retatrutide dosing charts and match neither trial. One climbs 2, 4, 6, 8, 10 and 12mg and reaches 12mg at week 21. The other is the retatrutide “label” listed on DailyMed, which is an export-only listing from a Guangzhou cross-border e-commerce company; its 2.5, 5, 7.5 and 10mg steps are tirzepatide’s escalation. Retatrutide has no official label yet. Lilly plans to file for FDA approval in the first quarter of 2027.

Retatrutide dosage in units

Retatrutide comes as a freeze-dried powder, so the dose in units depends on how much bacteriostatic water goes into the vial. On a U-100 insulin syringe, 100 units is 1mL. The math is one line: units = dose in mg ÷ strength in mg per mL × 100.

The simplest mix is 10mg per mL. One unit is then 0.1mg and every dose reads straight off the syringe: 2mg is 20 units, 9mg is 90. Each vial size gets there with its own volume of water:

From any of those mixes, each dose on the schedule is:

Two things change the chart. At 10mg per mL, 12mg is 120 units, more than one 1mL syringe holds; a 60mg vial mixed with 3mL brings it to 60 units in one injection. And the chart assumes the vial holds exactly its labeled amount, which the last section of this guide checks against real certificates. For any other vial and water combination, the Simms Research peptide calculator does the same math.

To mix, aim the stream at the glass rather than the powder, then roll the vial gently until the liquid is clear; shaking isn’t needed. Keep the mixed vial at 2–8°C (36–46°F). Simms Research sells bacteriostatic water for reconstitution, and its guide Do peptides need to be refrigerated? covers storage before and after mixing.

How long a retatrutide vial lasts

Once mixed, a vial runs on a clock. Simms Research’s storage guidance is to use a reconstituted vial within 28 days, and 28 days holds exactly five weekly doses: days 0, 7, 14, 21 and 28. The right vial for each step is the one that runs out in about five doses.

The fit is clean. The 10mg vial matches the 2mg step, the 20mg vial the 4mg step, the 30mg vial the 6mg step and the 60mg vial the 12mg dose, each with five doses inside the 28-day window. At lower doses, a larger vial holds more doses than 28 days allows.

Reaching 12mg on the Phase 3 schedule takes 84mg over the first 16 weeks. The first 12 weeks take 48mg, or 56mg on the Phase 2 path through 8mg. After that, holding a dose uses 16mg every four weeks at 4mg, 36mg at 9mg and 48mg at 12mg.

Retatrutide weight loss by dose

Every trial found the same shape: more weight loss at higher doses, with the gains shrinking at the top. The Phase 3 figures are Lilly’s efficacy estimand, the average for participants while they stayed on treatment.

The last step adds the least. Moving from 9mg to 12mg added 2.4 percentage points in TRIUMPH-1, 2.3 in TRIUMPH-4, 1.7 in TRIUMPH-2 and 1.0 in TRIUMPH-3. Moving from 4mg to 9mg added 6.9 points in TRIUMPH-1 and 6.4 in TRIUMPH-2. The 4mg dose is the efficient end of the range: 19.0% at 80 weeks in TRIUMPH-1, with fewer participants stopping for side effects (4.1%) than on placebo (4.9%).

Participants with type 2 diabetes lost less at every dose, the same pattern tirzepatide and semaglutide show in their diabetes trials. On the same doses, TRIUMPH-2 also cut A1C by up to 1.6 points, against 0.2 on placebo.

Retatrutide results timeline

At 24 weeks the Phase 2 8mg and 12mg groups were level, at 17.3% and 17.5%, because the 12mg group had only been at full dose since week 12. By week 48 the gap had opened to 1.4 points. Weight was still falling at week 48, and Lilly reported that participants in the TRIUMPH-1 extension kept losing weight through week 104.

Retatrutide starting dose and microdosing

2mg is the starting dose in every Phase 3 trial. The Phase 2 obesity trial tested why: its 4mg and 8mg groups each had one arm that started at 2mg and one that started at 4mg, and stomach side effects were more frequent with the 4mg start.

The Phase 2 diabetes trial showed the other side of that trade. At 36 weeks, the group that started directly at 4mg had lost 10.4%, against 7.9% for the group that stepped up from 2mg, in arms of about two dozen people each. A higher start brings the effect and the side effects forward together.

Below 2mg, the data thins out. 1mg a week, the lowest dose in the Phase 2 obesity trial, produced 7.2% weight loss at 24 weeks and 8.7% at 48, against 1.6% and 2.1% on placebo. 0.5mg a week, tested in people with type 2 diabetes, produced 3.2% at 36 weeks, level with placebo’s 3.0%. That makes 1mg the lowest dose that has beaten placebo on weight. Below it, the only weight data is that 0.5mg result.

Once a week or split into two injections

Every retatrutide trial dosed once a week. With a half-life of about six days, close to half of each injection is still circulating when the next one goes in, which is why a weekly schedule holds steady levels once the first month is over.

Splitting the weekly dose into two injections three or four days apart hasn’t been tested in a trial. It doesn’t change the weekly amount or the average level. It trims the peak after each injection and lifts the low point before the next, which makes it a tolerability choice, not a way to get more from the same dose. The weekly total stays fixed: a 4mg week becomes 2mg twice, 20 units each at 10mg per mL.

Daily dosing has no trial data and no pharmacokinetic reason behind it; a six-day half-life already smooths levels across the week.

Missed doses and changing the injection day

With no retatrutide label, the closest rule comes from tirzepatide, Lilly’s other weekly injection, whose half-life is shorter at about five days. Its label says to take a missed dose within 4 days (96 hours); after that, skip it and take the next dose on the usual day. Two doses need at least 3 days (72 hours) between them, which is also how to move the injection day.

A longer gap is a different situation. After three weeks without a dose, under a tenth of the steady level is left in circulation, close to where the body was before the first 2mg injection. The escalation schedule exists for exactly that starting point, which is why restarting a step or more below the old dose follows the same logic as the trials’ 2mg start.

Switching from tirzepatide or semaglutide

Milligrams don’t convert between these three peptides. Each has its own dose range, set by its own trials. What does compare is what each dose produced:

By outcome, semaglutide’s top dose (16.9%) sits below retatrutide 4mg (19.0%), and tirzepatide’s top dose (22.5%) sits between retatrutide 4mg and 9mg (25.9%). They are separate trials with different lengths and participants, so they place doses in the same neighborhood rather than make them equal.

No trial has studied switching yet, and the only tested starting point is still 2mg. With half-lives of five to seven days, the usual approach is to take the first retatrutide dose on the day the next tirzepatide or semaglutide dose would have been due, so the old peptide fades while the new one builds. Coming off a high tirzepatide dose, 2mg of retatrutide is a smaller effect, and some appetite coming back in the first weeks is expected.

The full side-by-side, from side effects at matched doses to cost per week, is in Retatrutide vs Tirzepatide: The Ultimate 2026 Comparison.

Retatrutide side effects by dose

Each common side effect was reported by fewer than half of participants at every dose, and the rates climb with dose. TRIUMPH-1, the largest trial, gives the cleanest comparison:

At 4mg, 71% of participants reported no nausea, and fewer stopped treatment for side effects than on placebo. At 12mg, 58% had no nausea and 11.3% stopped for a side effect, against 4.9% on placebo. Nausea, diarrhea, constipation and vomiting are the same stomach effects tirzepatide and semaglutide cause, and they are the reason doses climb in four-week steps. For how they run on tirzepatide, see What Are the Side Effects of Tirzepatide?

Dysesthesia is the one retatrutide adds: tingling or unusual sensitivity of the skin. It rose from 5.1% at 4mg to about 12% at 9 and 12mg in TRIUMPH-1, and reached 20.9% at 12mg in the smaller TRIUMPH-4, where Lilly described it as generally mild and rarely a reason to stop. Heart rate rose with dose in Phase 2, peaked around week 24 and eased after.

Why the vial’s real content changes the dose

Every unit in this guide assumes the vial holds exactly its label. A certificate of analysis states what it really holds, as net content. Simms Research has published six retatrutide batches: the five 10mg batches measured between 10.19mg and 11.95mg per vial, and the 20mg batch measured 19.82mg.

Those differences carry straight into every dose. The latest batch, 2026-G460, measured 10.68mg averaged across three vials. Mixed with 1mL, that is 10.68mg per mL, so 20 units holds 2.14mg rather than 2mg, and 2mg is 19 units. Batch R30 measured 11.95mg, where 20 units holds 2.39mg, 20% above the label. To correct any chart, divide the certificate’s net content by the water added to get the real strength.

A vial without a net-content figure gives no way to make that correction, and a certificate that doesn’t carry the batch number on the vial describes some other vial. These are the lines that matter for dosing:

Every batch is on the retatrutide lab results page, and How to Read a Peptide Certificate of Analysis covers each field.

Frequently asked questions

How many units is 2mg of retatrutide?

20 units on a U-100 insulin syringe when the vial is mixed to 10mg per mL: a 10mg vial with 1mL of water, a 20mg vial with 2mL or a 30mg vial with 3mL. A 10mg vial with 2mL makes it 40 units, and a 60mg vial with 3mL makes it 10 units.

How long does 10mg of retatrutide last?

Five weeks at 2mg a week, with the fifth dose on day 28, the end of a mixed vial’s window. At 4mg a week it covers two doses with 2mg left over.

Can you start retatrutide at 4mg?

The Phase 2 trials tested it. A 4mg start caused more stomach side effects than a 2mg start, which is why every Phase 3 trial began at 2mg.

What is the maximum dose of retatrutide?

12mg once a week. No trial has gone higher; 12mg was the top dose in Phase 1b, Phase 2 and every Phase 3 trial.

How much retatrutide per day?

None. The trials never dosed daily. Retatrutide is a weekly peptide: 2mg a week averages about 0.29mg a day, and its six-day half-life holds levels steady on one weekly injection.

What is the retatrutide dosage for women?

The same doses. No trial has dosed by sex, and women lost more on the same dose: in an analysis of the Phase 2 trial presented in October 2023, women on 8mg lost an average of 28.5% by week 48, and men 21.9%.

Is retatrutide dosed by body weight?

No. Every trial used fixed weekly doses whatever the participant weighed; TRIUMPH-1 participants averaged 248.5 lbs at the start. In Phase 2, participants with a BMI of 35 or higher lost up to 26.5% on average, and those under 35 up to 22.1%.

How much retatrutide for 3 months?

48mg for the first 12 weeks of the Phase 3 schedule (2, 4 and 6mg), or 56mg on the Phase 2 path through 8mg. In Simms Research vial sizes that is a 10mg, a 20mg and a 30mg vial, one per step.

What time of day should retatrutide be injected?

Any time. A peptide with a six-day half-life doesn’t follow the clock; what matters is keeping the same day each week. Meals don’t change how an injection under the skin is absorbed.

Is retatrutide approved?

Not yet. Lilly plans to submit it to the FDA in the first quarter of 2027. Simms Research sells retatrutide for laboratory research use only.