Retatrutide Dosage and Reconstitution Guide: Trial Figures, Worked Examples and Cost per mg

Retatrutide dosage and reconstitution guide: trial figures, worked examples and cost per mg

Retatrutide is a triple GLP-1, GIP and glucagon receptor agonist peptide studied in obesity, type 2 diabetes and liver fat trials. PrymaLab supplies it as lyophilised vials from Retatrutide 5mg to Retatrutide 60mg (seven sizes: 5, 10, 20, 30, 40, 50 and 60mg), plus a preloaded 15mg pen, for research use only.

• Molecule: single-chain 39-amino-acid peptide on a GIP backbone with a C20 fatty diacid, about 4.7 kDa, Lilly code LY3437943
• Class: triple agonist at the GIP, GLP-1 and glucagon receptors, given once weekly by subcutaneous injection in trials
• Studied for: obesity (NEJM 2023, phase 3 TRIUMPH), type 2 diabetes (Lancet 2023), MASLD (Nature Medicine 2024)
• Typical figures in the literature: 1 to 12 mg once weekly, 2 mg starting step, 36 to 80 weeks
• Storage: lyophilised vials frozen or refrigerated, away from light; reconstituted solution refrigerated, window per product page
• Forms and sizes at PrymaLab: Retatrutide 5mg, 10mg, 20mg, 30mg, 40mg, 50mg, 60mg vials, 15mg pen
• Cost per mg: $13.60 per mg (5mg vial) down to $3.12 (60mg vial); the pen is $5.67 per mg

Run any vial size and water volume through the peptide reconstitution calculator, and read the retatrutide vs tirzepatide guide for the receptor mechanism and the phase 3 comparison.

What the phase 2 and phase 3 trials dosed and how they titrated

Every published human trial of retatrutide has used once-weekly subcutaneous injection, and every arm above 1 mg started low and stepped up, so the maintenance figure in a trial arm was reached only after weeks at lower steps.

The phase 2 obesity trial (Jastreboff et al., NEJM 2023) randomised 338 adults with a BMI of 30 or higher, or 27 to under 30 with at least one weight-related condition, and without diabetes, to placebo or to retatrutide at 1, 4, 8 or 12 mg once weekly for 48 weeks. The 4 mg and 8 mg arms were each split by starting step, one sub-arm at 2 mg and the other at 4 mg; the 12 mg arm started at 2 mg, and the 1 mg arm had no escalation. Escalation steps were taken every 4 weeks over the first 12 weeks, so a participant in the 12 mg arm passed through 2, 4 and 8 mg on the way up.

The primary endpoint was percent change in body weight at 24 weeks: -7.2% at 1 mg, -12.9% at 4 mg, -17.3% at 8 mg and -17.5% at 12 mg, against -1.6% on placebo. At 48 weeks the figures were -8.7%, -17.1%, -22.8% and -24.2% against -2.1%. The 4 mg and 8 mg numbers pool the two starting-step sub-arms; taken separately at 48 weeks the 4 mg arms gave -16.3% and -17.8%, and the 8 mg arms -21.7% and -23.9%. Every participant in the 8 mg and 12 mg groups lost at least 5% of body weight, and 26% of the 12 mg group lost 30% or more. Weight was still falling at week 48 in the higher arms.

The phase 2 type 2 diabetes trial (Rosenstock et al., Lancet 2023) randomised 281 adults to placebo, dulaglutide 1.5 mg, or retatrutide at 0.5, 4, 8 or 12 mg once weekly for 36 weeks, again split by starting step in the higher arms. HbA1c at 24 weeks, the primary endpoint, fell by 2.02 percentage points in the 12 mg arm against 0.01 on placebo and 1.41 on dulaglutide. Body weight at 36 weeks fell by 16.94% in the 12 mg arm.

The phase 2a liver trial (Sanyal et al., Nature Medicine 2024) gave 98 adults with metabolic dysfunction-associated steatotic liver disease (MASLD) 1, 4, 8 or 12 mg once weekly, or placebo, for 48 weeks. Mean relative liver fat at 24 weeks changed by -42.9%, -57.0%, -81.4% and -82.4% across the four arms against +0.3% on placebo; by 48 weeks 93% of the highest-dose group had liver fat below 5%. The dose response was steep between 4 and 8 mg, then flat.

Phase 3 is Lilly's TRIUMPH programme. TRIUMPH-1 (NCT05929066) randomised 2,339 adults without type 2 diabetes who had obesity or overweight; every active arm started at 2 mg weekly and titrated to a 4, 9 or 12 mg maintenance step. Lilly reported topline results on 21 May 2026: mean weight change at 80 weeks of -19.0% at 4 mg, -25.9% at 9 mg and -28.3% at 12 mg against -2.2% on placebo, from an average baseline of 248.5 lb. In the 12 mg arm, 45.3% of participants lost 30% or more. A prespecified blinded extension to 104 weeks enrolled 532 participants who had a baseline BMI of 35 or higher and tolerated their assigned dose; those on 12 mg reached -30.3%. Phase 3 replaced the phase 2 8 mg step with 9 mg. The other registrations are TRIUMPH-2 (NCT05929079, type 2 diabetes with obesity or overweight), TRIUMPH-3 (NCT05882045, severe obesity with established cardiovascular disease) and TRIUMPH-4 (NCT05931367, obesity or overweight with knee osteoarthritis).

Retatrutide dosage in the literature

The table records what each study administered. It is a summary of trial design, not a protocol.

Reconstitution worked examples

PrymaLab ships retatrutide as lyophilised powder. Reconstitution means adding bacteriostatic water (water with 0.9% benzyl alcohol as a preservative, which is why it is used for multi-draw vials rather than plain sterile water), letting the powder dissolve, and recording the concentration. Three formulas cover every example below:

• Concentration (mg/ml) = peptide in the vial (mg) divided by water added (ml)
• Volume for a given quantity (ml) = quantity (mg) divided by concentration (mg/ml)
• Units on a U-100 insulin syringe = volume (ml) multiplied by 100, so 0.1 ml is 10 units

The water goes in slowly down the inside wall of the vial, and the vial is swirled rather than shaken, because agitation can damage a peptide of this length. Water volume is limited by the vial's capacity.

Retatrutide 5mg vial

With 1 ml of bacteriostatic water the concentration is 5 mg/ml, so 0.1 ml (10 units) holds 0.5 mg and 0.2 ml holds 1 mg. With 2 ml the concentration halves to 2.5 mg/ml and 0.1 ml holds 0.25 mg: finer resolution for small quantities, at the cost of larger draw volumes. Check any other volume on the peptide reconstitution calculator.

Retatrutide 10mg vial

The most common pairing is 10mg in 2 ml, which gives 5 mg/ml: 0.1 ml (10 units) equals 0.5 mg, 0.2 ml equals 1 mg, 0.4 ml equals 2 mg and 0.8 ml equals 4 mg. Mixed in 1 ml instead, the concentration is 10 mg/ml and 0.1 ml equals 1 mg, which keeps larger quantities inside a 1 ml syringe but makes 0.25 mg increments harder to read. The peptide reconstitution calculator prints the full volume table for either choice.

Retatrutide 20mg vial

20mg in 2 ml doubles the concentration to 10 mg/ml, so 0.1 ml equals 1 mg and 1.2 ml would equal 12 mg, above the 1 ml capacity of a standard insulin syringe. 20mg in 4 ml returns to 5 mg/ml, and the 10mg-in-2ml table applies with twice the draws per vial. Enter 20mg and any water volume in the peptide reconstitution calculator to see both options side by side.

Retatrutide 30mg vial

30mg in 3 ml gives 10 mg/ml (0.1 ml equals 1 mg); 30mg in 2 ml gives 15 mg/ml (0.1 ml equals 1.5 mg, 0.8 ml equals 12 mg). At 15 mg/ml a one-unit (0.01 ml) reading error is 0.15 mg, three times the error at 5 mg/ml, so higher concentrations demand more careful reading of the graduations. The peptide reconstitution calculator handles the 40, 50 and 60mg sizes the same way.

Storage before and after reconstitution

Lyophilised retatrutide is stable as a dry powder when kept cold and dark: a freezer at -20°C for long-term storage, or a refrigerator at 2 to 8°C for vials that will be used within weeks, in the original carton away from light. Vials are brought to room temperature before the seal is punctured, so condensation does not form on cold powder.

After reconstitution the peptide is in solution and its stability window shortens. Reconstituted vials are kept refrigerated at 2 to 8°C, away from light, and are not frozen, since ice crystals damage dissolved peptide. The benzyl alcohol in bacteriostatic water limits microbial growth over repeated draws but does not stop chemical degradation of the peptide. The solution is used within the window stated on the product page for that vial size; those per-product figures govern the lot in hand.

Retatrutide cost per mg across PrymaLab's seven sizes

Retatrutide cost depends on vial size more than on vendor. The table uses PrymaLab's current "from" prices and divides by the milligrams in the vial.

The Preloaded Autoinjector | Retatrutide | 3ml Pen | 15mg is $84.99, or $5.67 per mg. It comes in solution rather than as powder, so it skips the reconstitution step; the product page gives its fill volume and concentration.

Larger vials cost less per mg because most of the cost of a vial is fixed per unit. The glass vial, stopper and crimp, the lyophilisation run, the HPLC and mass spectrometry testing behind the certificate of analysis, labelling, packaging and shipping cost the same whether the vial holds 5 mg or 60 mg; the peptide is the only cost that scales with milligrams. The 60mg vial costs 2.75 times the 5mg price for 12 times the peptide, which is why the per-mg figure falls from $13.60 to $3.12. The smaller sizes make sense when a lot needs to be tested before committing to volume, or when a reconstituted vial would otherwise sit past its storage window.

How to buy retatrutide for research

Retatrutide is an investigational compound with no marketing approval and no prescription product, so "how to get retatrutide" resolves to one route: purchasing research-grade material from a vendor that sells it for laboratory use. PrymaLab is a US vendor in Ashland, Kentucky, veteran owned, and ships lyophilised retatrutide in seven sizes plus a preloaded pen, all for research use only and not for human consumption:

• Retatrutide 5mg, from $67.99
• Retatrutide 10mg, from $84.99
• Retatrutide 20mg, from $101.99
• Retatrutide 30mg, from $126.99
• Retatrutide 40mg, from $149.99
• Retatrutide 50mg, from $169.99
• Retatrutide 60mg, from $186.99
• Preloaded Autoinjector | Retatrutide | 3ml Pen | 15mg, from $84.99

The certificate of analysis (COA) is the document that ties a lab test to the vial. A useful COA lists the product name and lot number, which must match the vial label; the test date; identity confirmation by mass spectrometry, with the observed mass next to the theoretical mass for retatrutide (about 4,731 Da); purity by HPLC as a percentage, with the method noted; net quantity; and appearance (white to off-white lyophilised powder). A COA without a lot number, or one that states purity with no method, is not evidence of anything. Bacteriostatic water is sold separately in 3ML and 10ML sizes, and the longer retatrutide purchase guide covers mechanism and trial history in more depth.

Retatrutide vs tirzepatide vs semaglutide

Each of the three is a once-weekly incretin-class agonist developed by a large pharmaceutical company for obesity and type 2 diabetes. They differ in receptors, development stage and the sizes available for research.

The receptor discussion, including why the glucagon receptor matters for liver fat and why the GIP contribution is still debated, is in the retatrutide vs tirzepatide guide.

Frequently asked questions

Key takeaways

• Trials dosed retatrutide once weekly by subcutaneous injection at 1 to 12 mg, with 2 mg starting steps: escalation every 4 weeks in phase 2, titration to 4, 9 or 12 mg in phase 3.
• The phase 2 obesity trial reported -24.2% body weight at 48 weeks on 12 mg; TRIUMPH-1 reported -28.3% at 80 weeks, and -30.3% at 104 weeks in an extension limited to participants with a baseline BMI of 35 or higher.
• Reconstitution is arithmetic: 10mg in 2 ml is 5 mg/ml (0.1 ml = 0.5 mg); 20mg in 2 ml is 10 mg/ml (0.1 ml = 1 mg).
• Lyophilised vials are stored frozen or refrigerated away from light; reconstituted solution is refrigerated and used within the window on the product page.
• Cost per mg falls from $13.60 (5mg vial) to $3.12 (60mg vial) because per-vial costs are fixed; the 15mg pen is $5.67 per mg.

Related products

• Retatrutide 5mg
• Retatrutide 10mg
• Retatrutide 20mg
• Retatrutide 30mg
• Retatrutide 40mg
• Retatrutide 50mg
• Retatrutide 60mg
• Preloaded Autoinjector | Retatrutide | 3ml Pen | 15mg
• BAC Water (Bacteriostatic Water) 3ML
• BAC Water (Bacteriostatic Water) 10ML

References

1. Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023;389(6):514-526. https://doi.org/10.1056/NEJMoa2301972
2. Rosenstock J, Frias J, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. Lancet. 2023;402(10401):529-544. https://doi.org/10.1016/S0140-6736(23)01053-X
3. Sanyal AJ, Kaplan LM, Frias JP, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nat Med. 2024;30(7):2037-2048. https://doi.org/10.1038/s41591-024-03018-2
4. 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. https://doi.org/10.1016/S0140-6736(22)02033-5
5. Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.e9. https://doi.org/10.1016/j.cmet.2022.07.013
6. ClinicalTrials.gov. NCT05929066: a study of retatrutide (LY3437943) in participants who have obesity or overweight (TRIUMPH-1). https://clinicaltrials.gov/study/NCT05929066
7. AJMC. Retatrutide achieves up to 30.3% average weight loss in phase 3 TRIUMPH-1 trial. May 2026. https://www.ajmc.com/view/retatrutide-achieves-up-to-30-3-average-weight-loss-in-phase-3-triumph-1-trial
8. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. https://doi.org/10.1056/NEJMoa2206038
9. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. https://doi.org/10.1056/NEJMoa2032183