Retatrutide Dosage Chart and Calculator: Protocol, Trial Doses
Retatrutide dosage chart: units per dose by vial size for the 2-12 mg weekly common protocol, a calculator, and the Phase 2 and 3 trial doses. Not FDA-approved.
The short version
Retatrutide has no approved dose because it has no approved product. Clinic and dosing-guide sources report a common protocol. It is a once-weekly subcutaneous injection starting at 2 mg and titrating every 4 weeks to a 4-12 mg maintenance dose. The Phase 3 program used the same schedule. It is labelled here as common practice, not a trial-established or FDA-approved dose. Any vial sold outside a trial is not made or monitored the same way.
- Peer-reviewed dosing data come from two trials. A Phase 2 obesity trial used 1-12 mg weekly for 48 weeks. Phase 3 TRANSCEND-T2D-1 in diabetes used 4, 9 or 12 mg weekly for 40 weeks.
- The TRIUMPH-1 Phase 3 obesity figures (4, 9, 12 mg) come from a company press release, not a peer-reviewed paper or an FDA label.
- Reconstitution and volume math belongs on a calculator, not guessed from a forum post.
- No regulator has established any dose as safe or effective. This page reports what trials tested, not what to take.
Retatrutide has no approved dose, because it has no approved product. This page reports what human trials used. That means a published Phase 2 study, a published Phase 3 diabetes trial, and the sponsor’s own topline figures from its largest Phase 3 obesity trial. It is not a recommendation for what anyone should take. For the full picture on what retatrutide is and its trial program, see the main retatrutide guide.
US legal status - Research use only
Retatrutide has no FDA-approved product and no approved indication or dose. FDA states it cannot legally be compounded, because it is not a component of an FDA-approved drug and has not been found safe and effective for any condition.
AU legal status - Not on the ARTG
Not on the ARTG and not approved for supply in Australia.
Regulators reach their own conclusions on their own timelines. Where these two disagree, the difference is the point - not an error.
Retatrutide dosage: the common protocol
Clinic and dosing-guide sources describe a once-weekly subcutaneous injection starting at 2 mg. The dose steps up every 4 weeks (2 mg, 4 mg, 6 mg, 9 mg) to a 4-12 mg maintenance dose. They describe the same schedule for the Phase 3 program. This is common practice, not a trial-established or FDA-approved dose.
Common protocol
What is commonly used, not a dose established in trials. No regulator has set a dose for Retatrutide.
- Dose per administration
- 2-12 mg
- How often
- once weekly, starting at 2 mg and titrating up every 4 weeks to a 4-12 mg maintenance dose
- Route
- Subcutaneous injection
- Cycle length
- No set length in common use
Clinic and dosing-guide sources describe the same 4-week step-up schedule used in the Phase 3 program: 2 mg, then 4 mg, 6 mg, 9 mg, up to a 12 mg maintenance dose, each step held for 4 weeks. Sources describe this as the trial schedule, not an established personal cycle length.
Plan a cycle in the protocol builder or work out injection volume in the dosage calculator.
The common Retatrutide dose is 2-12 mg, once weekly, starting at 2 mg and titrating up every 4 weeks to a 4-12 mg maintenance dose. From a 10 mg vial mixed with 1 mL of bacteriostatic water, 7 mg is 70 units (0.7 mL) on a U-100 insulin syringe.
Retatrutide 10 mg vial: units per dose
Full 10 mg vial page: mixing, doses per vial, how long it lasts →
| Water added | Concentration | 1 unit = | 2 mg | 7 mg | 12 mg |
|---|---|---|---|---|---|
| 1 mL | 10 mg/mL | 100 mcg | 20 units | 70 units | over 100 units |
| 2 mL | 5 mg/mL | 50 mcg | 40 units | over 100 units | over 100 units |
| 3 mL | 3.33 mg/mL | 33.33 mcg | 60 units | over 100 units | over 100 units |
All Retatrutide vial sizes: 5 mg · 10 mg · 20 mg · 30 mg · 40 mg · 50 mg · 60 mg
Units are on a standard U-100 insulin syringe (100 units = 1 mL), rounded to the nearest half unit - half-unit marks are on 0.3 mL syringes. Water volumes are examples: more water means more units per dose, not more doses per vial. For any other vial or dose, use the calculator below.
How many 10 mg vials a cycle takes
| Scenario | Dose | Doses a week | Per 4 weeks | Total | 10 mg vials |
|---|---|---|---|---|---|
| Low end of the common protocol | 2 mg | 1 | 4 | 8 mg | 1 |
| High end of the common protocol | 12 mg | 1 | 4 | 48 mg | 5 |
Whole vials, rounded up. Plan a cycle with your own numbers in the protocol builder. Keep mixed vials cold and use them within the window in how long reconstituted peptides last; where to inject: subcutaneous injection sites.
Retatrutide doses used in human studies
A Phase 2, randomised, double-blind, placebo-controlled trial Jastreboff 2023 - Jastreboff AM, Kaplan LM, Frías JP et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526., in the references below enrolled 338 adults with obesity (BMI ≥30) or overweight with a weight-related condition (BMI 27-29.9), without type 2 diabetes. Retatrutide was given as a subcutaneous injection once weekly. Participants were assigned to one of several target doses: 1 mg, 4 mg, 8 mg or 12 mg. The higher doses were reached through a titration that started some arms at 2 mg or 4 mg. Treatment ran 48 weeks, with the trial’s own primary endpoint measured at week 24.
| Target dose (weekly) | Reported mean weight change at 48 weeks |
|---|---|
| 1 mg | -8.7% |
| 4 mg | -17.1% |
| 8 mg | -22.8% |
| 12 mg | -24.2% |
| Placebo | -2.1% |
At the 12 mg dose, the paper reports that 100% of participants reached at least 5% weight loss. It also reports 93% reached at least 10% and 83% reached at least 15%. It describes the most common adverse events across all dose groups as gastrointestinal, dose-related and mostly mild to moderate. A peer-reviewed trial measured this in its own participants under clinical monitoring. It is not a dose this page recommends.
A Phase 3, randomised, double-blind, placebo-controlled trial, TRANSCEND-T2D-1 Bajaj 2026 - Bajaj HS, Welch M, Shah P et al. Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. Lancet. 2026;407(10546):2402-2413., in the references below, enrolled 537 adults with type 2 diabetes not controlled by diet and exercise. They received 4 mg, 9 mg or 12 mg retatrutide, or placebo. The dose was a subcutaneous injection once weekly for 40 weeks. HbA1c fell by 1.69 to 1.94 percentage points across the three doses, against 0.81 on placebo. Body weight fell by 11.5% to 15.3%, against 2.6%. Between 2% and 5% of those on retatrutide stopped because of adverse events, against none on placebo.
What the Phase 3 topline figures add (not peer-reviewed)
Eli Lilly’s own press release on its completed Phase 3 trial, TRIUMPH-1, reports three dose arms: 4 mg, 9 mg and 12 mg, weekly, over 80 weeks. It gives weight-loss and discontinuation figures by dose. The main retatrutide guide describes that trial and its numbers in full. As of this writing, those results have not been posted to the public trial registry or published in a peer-reviewed journal. They sit alongside the peer-reviewed Phase 2 data above, not instead of it.
Reconstitution and injection volume: use the calculator, not a guess
Turning a target dose into an injection volume depends on how a specific vial was reconstituted: how much diluent, and what concentration results. This page cannot know that for any given vial. The dosage calculator walks through vial strength, diluent volume and target amount. It does the math. It does not tell you what dose to use.
What is not established
- No approved dose exists, for any population, indication or duration, because no product has completed FDA review.
- No dose has been proven safe or effective by any regulator. The figures above are what specific trials measured in their own participants, not a demonstrated general result.
- The half-life comes from one small trial. A 12-week Phase 1b trial in 72 people with type 2 diabetes measured a half-life of about 6 days Urva 2022 - Urva S, Coskun T, Loh MT et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet. 2022;400(10366):1869-1881., in the references below. Its investigators said this suggests suitability for once-weekly dosing; see the main guide. It has not been measured in a vial sold outside the trial system.
- The common protocol above is not the trial protocol. It reflects what clinic and dosing-guide sources describe as typical practice, not a dose any trial, paper or regulator has established as safe or effective.
Who should not use retatrutide
No FDA-reviewed contraindication list exists for retatrutide, because no such review has happened. As general context, the related, FDA-approved GLP-1 drugs semaglutide and tirzepatide are both contraindicated with a personal or family history of medullary thyroid carcinoma. The same applies to Multiple Endocrine Neoplasia syndrome type 2. Neither has been studied as safe in pregnancy or breastfeeding.
Retatrutide’s own trials have not published a comparable contraindication list. Do not self-direct an unapproved compound with no FDA-reviewed label around any medical condition, current medication or pregnancy status.
Retatrutide side effects and risks
The Phase 2 trial and the sponsor’s Phase 3 topline report both describe gastrointestinal adverse events as the most common. They include nausea, diarrhoea, constipation and vomiting, and they rise with dose. In the published TRANSCEND-T2D-1 trial, the gastrointestinal events were mostly mild to moderate and eased over time Bajaj 2026 - Bajaj HS, Welch M, Shah P et al. Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. Lancet. 2026;407(10546):2402-2413., in the references below.
Phase 3 topline data also reports discontinuation due to adverse events rising from 4.1% at 4 mg to 11.3% at 12 mg, against 4.9% on placebo. Beyond what these trials report, there is no long-term safety data past their own follow-up windows. A vial bought outside the trial system carries no verified content, purity or strength.
Related
- Retatrutide: what it is and what the trials show
- Dosage calculator
- Cagrilintide dosage: what the studies used
- Retatrutide vs tirzepatide
- Are peptides safe?
Retatrutide dosage calculator
Preset to a 5 mg vial and 2,000 mcg, the low end of the common protocol. Enter your own vial size, water and dose to get the syringe units to draw.
Your vial
Printed on the vial. There is no standard size - enter what yours says.
This changes how much you draw - never how many doses the vial holds.
100 units per mL. 1 unit = 0.01 mL. This is what almost every insulin syringe sold is, in every barrel size.
Capacity only. A 1 mL U-100 syringe holds 100 units - the scale decides that, not the barrel.
Draw this much
= 0.8 mL on a 1 mL U-100 syringe
- Concentration
- 2,500 mcg/mL
- Exact volume
- 0.8 mL
- Dose you actually get
- 2,000 mcg
- Doses per vial(unaffected by water volume)
- 2
Where to buy Retatrutide for research
Each vendor is checked against my vendor checklist.
1.Next Level PharmFeatured
10 mg vial
- No FDA warning letter found
- Names its testing lab
- Batch COAs published
- Takes card payment
2.Spartan Peptides
GLP-3(Reta) 6 mg vial
- No FDA warning letter found
- Names its testing lab
Common questions
What is the usual retatrutide dose?
Clinic and dosing-guide sources describe a common protocol of once-weekly subcutaneous injections starting at 2 mg. The dose steps up every 4 weeks (2 mg, 4 mg, 6 mg, 9 mg) to a 4-12 mg maintenance dose, mirroring the Phase 3 program's schedule. That is common practice reported outside the trial system. No regulator has approved it, and no trial has established it as safe or effective outside a study.
What dose of retatrutide did the human trials use?
A published Phase 2 trial in 338 adults with obesity or overweight tested subcutaneous retatrutide at 1 mg, 4 mg, 8 mg and 12 mg. It was dosed once weekly for 48 weeks. Some arms started at a lower dose, 2 mg or 4 mg, before reaching their target. That is trial design reported in a peer-reviewed paper, not a recommended dose for anyone outside that trial.
Is there an FDA-approved retatrutide dose?
No. Retatrutide has no FDA-approved product and no approved dose. The Phase 2 doses above come from a published trial. Two Phase 3 trials tested the same 4 mg, 9 mg and 12 mg weekly doses. TRANSCEND-T2D-1, in type 2 diabetes, is published. TRIUMPH-1, in obesity, has so far reported results only through the sponsor's own press release. None of these is FDA review or an approved label.
How often and for how long was retatrutide dosed in the trial?
Once weekly for 48 weeks in the published Phase 2 trial, and once weekly for 40 weeks in the published Phase 3 TRANSCEND-T2D-1 diabetes trial. The larger TRIUMPH-1 obesity trial also dosed weekly, over 80 weeks, according to the sponsor's topline report. That report has not been published in a peer-reviewed journal or posted to the public trial registry as of this writing.
How do I work out reconstitution and injection volume?
That is arithmetic, not a dosing decision. It depends on the concentration of a specific vial and diluent, which this page cannot know for you. Use the dosage calculator to work through the math for your vial and target amount. It does not tell you what dose to use.
What are the main risks?
In the sponsor's reported Phase 3 topline data, discontinuation due to adverse events rose with dose. It was 4.1% at 4 mg, 6.9% at 9 mg and 11.3% at 12 mg, against 4.9% on placebo. Gastrointestinal effects (nausea, diarrhoea, constipation, vomiting) were the most common. The published Phase 2 trial also reported gastrointestinal adverse events as dose-related. Beyond that, there is no FDA-reviewed safety label, no confirmed long-term data, and no quality control on vials sold outside the trial system.
When should I stop and get medical care?
Get emergency care (call 911 in the US) for signs of a severe allergic reaction. Do the same for severe or persistent vomiting with signs of dehydration, or severe abdominal pain (which can signal pancreatitis). Also seek care for a lump in the neck, trouble swallowing or persistent hoarseness. If you have taken an unknown or excessive amount of anything sold as retatrutide, call Poison Control at 1-800-222-1222. None of this is a substitute for a clinician who knows your history.
References (4 sources)
Bibliographic detail is fetched from PubMed, not written by me - so a citation here cannot drift from the paper it names. Study design comes from PubMed's own tags rather than my judgement.
- 1.Jastreboff AM, Kaplan LM, Frías JP et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526.Randomised trialPMID 37366315
- 2.Bajaj HS, Welch M, Shah P et al. Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. Lancet. 2026;407(10546):2402-2413.Randomised trialPMID 42250575
- 3.Urva S, Coskun T, Loh MT et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet. 2022;400(10366):1869-1881.Randomised trialPMID 36354040
- 4.FDA - retatrutide cannot be used in compounding under federal law; not a component of an FDA-approved drug and not found safe and effective for any condition.- US Food and Drug Administrationregulatory