How much water do I add to a 40 mg Retatrutide vial?

There is no single correct amount: water changes how many units a dose is, not how many doses the vial holds. With 1 mL the vial is 40 mg/mL and 7 mg is 17.5 units (0.18 mL) on a U-100 insulin syringe. The units table gives 1, 2, 5 mL.

How many doses are in a 40 mg Retatrutide vial?

20 doses at 2 mg, 5 doses at 7 mg, 3 doses at 12 mg.

How long does a 40 mg Retatrutide vial last?

At 7 mg a dose and once weekly, about 5 weeks. How long a mixed vial keeps is a separate limit; see storage below.

How many 40 mg vials do I need for a 4-week run?

1 vial at 2 mg 1 time a week for 4 weeks; 2 vials at 12 mg 1 time a week for 4 weeks.

What does 1 unit equal in a 40 mg Retatrutide vial?

400 mcg with 1 mL, 200 mcg with 2 mL, 80 mcg with 5 mL of bacteriostatic water, on a U-100 syringe.

Research use only · common protocol

Retatrutide 40 mg vial dosage

A 40 mg Retatrutide vial mixed with 1 mL of bacteriostatic water gives 40 mg/mL, so 7 mg is 17.5 units (0.18 mL) on a U-100 insulin syringe. At 7 mg a dose, one vial holds 5 doses.

Email me this plan, with a reminder before the vial's 28-day mark →

The common Retatrutide protocol is 2-12 mg, once weekly, starting at 2 mg and titrating up every 4 weeks to a 4-12 mg maintenance dose - common practice, not a dose established in trials. Evidence, side effects and legal status are on the full Retatrutide dosing page.

Retatrutide 40 mg vial at a glance

Vial: 40 mg of Retatrutide per vial
Common dose: 2-12 mg
How often: once weekly, starting at 2 mg and titrating up every 4 weeks to a 4-12 mg maintenance dose
Mixing example: 1 mL bacteriostatic water = 40 mg/mL; 1 unit = 400 mcg
Doses per vial: 20 at 2 mg · 5 at 7 mg · 3 at 12 mg
Route: Subcutaneous injection

What Retatrutide is

Class:: Triple GIP/GLP-1/glucagon receptor agonist
Also called:: LY3437943
Used for:: Investigational in Phase 3 trials for obesity, type 2 diabetes and related conditions. Not approved for any indication in the US. Sold outside the trial system as an unapproved research chemical, often alongside semaglutide and tirzepatide.
Human evidence:: Moderate human evidence. Multiple randomised, double-blind, placebo-controlled Phase 3 trials have been run in humans, confirmed this session on the ClinicalTrials.gov registry: a completed obesity trial (TRIUMPH-1, 2,335 participants, primary endpoint at week 80) and an ongoing roughly 10,000-person cardiovascular and kidney outcomes trial (TRIUMPH-Outcomes). Neither has posted results to the public registry, and TRIUMPH-1's figures so far are topline numbers from the sponsor's own press release. Peer-reviewed results have been published from other trials: a 48-week Phase 2 obesity trial of 338 adults (NEJM, 2023; -24.2% body weight on 12 mg against -2.1% on placebo) and TRANSCEND-T2D-1, a 40-week Phase 3 trial of 537 adults with type 2 diabetes (The Lancet, 2026; weight -11.5% to -15.3% against -2.6%). All were funded by the developer, and none of the data has been reviewed by FDA.
Half-life:: About 6 days, from a 12-week Phase 1b trial in 72 people with type 2 diabetes, whose investigators said its pharmacokinetics suggest suitability for once-weekly dosing.
US status:: Research use only. Not FDA-approved for any indication. FDA states plainly that retatrutide cannot be used in compounding under federal law, because it is not a component of an FDA-approved drug and has not been found safe and effective for any condition, and it has warned telehealth companies, API distributors and outsourcing facilities specifically over unapproved retatrutide. Eli Lilly (the trial sponsor) has reported topline results from its Phase 3 obesity trials (one Phase 3 diabetes trial, TRANSCEND-T2D-1, is published) and, as reported in August 2026, plans to submit a biologics license application to FDA in the first quarter of 2027.

The full picture, with every study: Retatrutide guide.

Units per dose: Retatrutide 40 mg vial

Water added	Concentration	1 unit =	2 mg	7 mg	12 mg
1 mL	40 mg/mL	400 mcg	5 units	17.5 units	30 units
2 mL	20 mg/mL	200 mcg	10 units	35 units	60 units
5 mL	8 mg/mL	80 mcg	25 units	87.5 units	over 100 units

U-100 insulin syringe (100 units = 1 mL), to the nearest half unit. Water volumes are examples. Other numbers: dosage calculator.

Every dose from 2 mg to 12 mg, in units

With 1 mL of water in a 40 mg vial (40 mg/mL). Every dose across the common range, so you can read off any dose. The sources give a range, not a week-by-week schedule.

Dose	Draw on a U-100 syringe	Volume	Doses per vial
2 mg	5 units	0.05 mL	20
4 mg	10 units	0.1 mL	10
6 mg	15 units	0.15 mL	6
8 mg	20 units	0.2 mL	5
10 mg	25 units	0.25 mL	4
12 mg	30 units	0.3 mL	3

How many doses a 40 mg vial holds

Dose	Doses per vial	Weeks per vial
2 mg	20	20
7 mg	5	5
12 mg	3	3

Weeks per vial at the common frequency (once weekly, starting at 2 mg and titrating up every 4 weeks to a 4-12 mg maintenance dose). Doses per vial do not depend on how much water you add.

Email me my Retatrutide 40 mg vial plan

Pick your water volume and dose and I will email you the numbers for this vial - units, volume, doses per vial and how long it lasts - plus the mixing and storage steps, and a reminder before the mixed vial reaches 28 days.

The common Retatrutide protocol

Dose	2-12 mg per injection
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	No cycle length is stated consistently by the sources
Break	No break length is stated consistently by the sources
Sources agree?	Yes, the sources give the same protocol

Common practice from the vendors and clinics that publish it, not a dose tested in trials. Where it comes from: [1], [2]. I do not give week-by-week titration: none of these sources states one.

Supplies for four weeks with 40 mg vials

Counted for the low and high ends of the common protocol over four weeks, since the sources give no fixed cycle length, mixing each vial with 1 mL of water. One new syringe per injection.

Plan	Injections	40 mg vials	Insulin syringes	Bacteriostatic water	Alcohol swabs
2 mg, 1×/week, 4 weeks	4	1	4	1 mL (1 × 10 mL bottle)	10 (1 × 100-pack)
12 mg, 1×/week, 4 weeks	4	2	4	2 mL (1 × 10 mL bottle)	12 (1 × 100-pack)

Arithmetic on the protocol and this vial size. Swabs: two per vial mixed (both stoppers) and two per injection (vial stopper and skin). An opened multi-dose vial has a use-by date (see storage), which on a slow schedule can matter more than the dose count. Plan your own numbers with the protocol builder.

How to mix a 40 mg Retatrutide vial

For this vial: 1 mL of bacteriostatic water makes 40 mg/mL, so 7 mg is 17.5 units (0.18 mL) on a U-100 insulin syringe. Pick a different volume from the units table if you want bigger or smaller draws; the number of doses stays the same.

Wipe the rubber stoppers of both the peptide vial and the bacteriostatic water vial with an alcohol swab and let the alcohol dry. ^[3][4]
With a new sterile needle and syringe, draw up the amount of bacteriostatic water you have chosen for the dilution. ^[3][4][5]
Inject the water into the peptide vial by aiming the stream against the inside glass wall, which helps prevent foaming. ^[6]
Swirl or roll the vial gently until the powder has fully dissolved; do not shake it. Do not inject the solution if it is cloudy or has particles in it. ^[3][4][6]
Label the vial with the date and time it was mixed, the amount of water added and how long it can be used after mixing. ^[3]
Store the mixed vial in the refrigerator at 2-8°C (36-46°F) and do not freeze it. ^[6]

Step by step with pictures: how to reconstitute peptides. About the water itself: bacteriostatic water.

Storing Retatrutide vials

Freeze-dried (lyophilized) peptide keeps far longer than peptide in solution; peptide suppliers advise storing the powder at -20°C away from bright light. ^[7]
Protect peptide vials from heat and light. ^[7][8]
Avoid repeated freeze-thaw cycles; a prescription peptide label also says not to freeze a vial once it has been mixed. ^[6][7]
Once a multi-dose vial, such as bacteriostatic water, has been opened (needle-punctured), date it and discard it within 28 days unless its manufacturer states another date. ^[9][10]

More detail: peptide storage and shelf life.

Injecting safely

Clean the injection site with an alcohol swab and let the skin dry completely before injecting. ^[11][12]
Pinch up a fold of skin and fat (not muscle) and insert the needle at a 45- to 90-degree angle: 90 degrees where there is enough fatty tissue, 45 degrees where there is little. ^[11][12][13]
Pulling back on the plunger (aspiration) is not necessary for a subcutaneous injection, because the chance of the needle being in a blood vessel is small. ^[11]
Inject slowly, at roughly 10 seconds per mL. ^[11]
Common sites are the belly, the thigh and the upper arm; rotate sites, keeping each injection at least 1 inch (2.5 cm) from the last. ^[6][11][12]

Hygiene and warning signs

Use a new sterile needle and syringe for every injection and every time you enter a vial; never reuse them. ^[5][9][12]
Never share needles, syringes or pens with anyone, even if the needle is changed; unsafe injection practices spread hepatitis B, hepatitis C and HIV. ^[5][8][9]
Put used needles and syringes in a sharps disposal container straight away (FDA-cleared if possible), never loose in the trash, recycling or toilet, and dispose of the container following your community's guidelines. ^[14][15]
Contact a health care provider if the injection site shows signs of infection, such as redness, swelling, red streaks or a fever. ^[12]

Where to inject: subcutaneous injection sites.

How Retatrutide works

Retatrutide (development code LY3437943) is a single peptide that activates three receptors: glucagon, GIP and GLP-1. In laboratory tests its glucagon and GLP-1 receptor activity is balanced, with stronger activity at the GIP receptor. ^[16]
In obese mice, the glucagon-receptor activity added a rise in energy expenditure on top of the reduced food intake driven by the GIP and GLP-1 receptors, and weight loss was greater as a result. That energy-expenditure effect was shown in mice, not established in people. ^[16]
In a 12-week trial in people with type 2 diabetes, its pharmacokinetics were dose-proportional with a half-life of about 6 days, which the investigators judged suitable for once-weekly dosing. ^[17]

What the Retatrutide research found

Human evidence: moderate human evidence. Each result says what was studied.

Human studyIn a 48-week phase 2 randomised, placebo-controlled trial of 338 adults with obesity or overweight, mean weight change was -8.7% on 1 mg, -17.1% on 4 mg, -22.8% on 8 mg and -24.2% on 12 mg weekly, against -2.1% on placebo. ^[18]
Human studyIn the same trial, 83% of those on 12 mg lost at least 15% of body weight by week 48, against 2% on placebo. ^[18]
Human studyIn a phase 2 trial of 281 adults with type 2 diabetes, HbA1c fell by up to 2.02 percentage points at 24 weeks on retatrutide against 0.01 on placebo and 1.41 on dulaglutide 1.5 mg, and body weight fell by up to 16.94% at 36 weeks against 3.00% on placebo. ^[19]
Human studyIn TRANSCEND-T2D-1, a 40-week phase 3 trial of 537 adults with type 2 diabetes not controlled by diet and exercise, HbA1c fell by 1.69-1.94 percentage points across the 4, 9 and 12 mg doses against 0.81 on placebo, and weight fell by 11.5-15.3% against 2.6%. ^[20]
Human studyIn a 12-week phase 1b trial of 72 people with type 2 diabetes, placebo-adjusted weight loss appeared dose-dependent, reaching 8.96 kg in the highest-dose group. ^[17]

Retatrutide side effects and risks

Retatrutide has no FDA-reviewed label; these safety data come from published phase 2 and 3 trials lasting up to 48 weeks, all funded by the developer.

Human studyIn the 48-week phase 2 obesity trial, gastrointestinal events were the most common adverse effects. They rose with dose, were mostly mild to moderate, and were partly reduced by starting at 2 mg rather than 4 mg. ^[18]
Human studyHeart rate rose in a dose-dependent way in the phase 2 obesity trial, peaking at 24 weeks and declining afterwards. ^[18]
Human studyIn the phase 2 type 2 diabetes trial, mild-to-moderate gastrointestinal events (nausea, diarrhoea, vomiting, constipation) affected 35% of retatrutide recipients - from 13% on 0.5 mg to 50% in the fastest 8 mg escalation group - against 13% on placebo. No severe hypoglycaemia was reported. ^[19]
Human studyIn the 40-week TRANSCEND-T2D-1 trial, 2-5% of retatrutide recipients stopped because of adverse events against 0% on placebo, and gastrointestinal events eased over time. Two deaths, both in the 4 mg group, were judged unrelated to the drug. ^[20]

Other things to know

No FDA-approved product exists, so there is no FDA-reviewed safety label, no confirmed adverse-reaction rate and no defined dose - unlike semaglutide and tirzepatide, which have both.
Human safety data come from developer-funded trials, none reviewed by FDA. Per the sponsor's own press release, discontinuation due to adverse events rose with dose in its largest completed trial: 4.1% at 4 mg, 6.9% at 9 mg and 11.3% at 12 mg, against 4.9% on placebo. The published Phase 2 obesity trial reported dose-related gastrointestinal events and a dose-dependent rise in heart rate that peaked at 24 weeks.
FDA has taken enforcement action - warning telehealth companies, active pharmaceutical ingredient distributors and outsourcing facilities - specifically over unapproved retatrutide, and it cannot legally be compounded under any circumstance.
It activates a third receptor (glucagon) that semaglutide and tirzepatide do not. Whether that adds any distinct long-term risk in humans has not been established through FDA review, because no such review has happened.

Reported side effects and what the studies measured: Retatrutide side effects.

Where this vial size comes from

Retatrutide is sold as a 40 mg vial by the pages below, each checked on the date shown. I list them as evidence that this size exists, not as a recommendation to buy from them.

Futureproof PeptidesvendorLists it as: "Retatrutide 40mg Vial" - "Total content: 40mg per vial" · checked 2026-09-28
PSPeptidesvendorLists it as: MG dropdown includes 40mg option with COA · checked 2026-09-28

The doses come from the sourced common protocol on the Retatrutide dosing page, and every number on this page is arithmetic on those doses and this vial size.

Other Retatrutide vial sizes

Where to buy Retatrutide for research

Sold for research use only. Listed by Next Level Pharm and Spartan Peptides; compare them on my vendors page or see the listing on the Retatrutide page.

Questions

How much water do I add to a 40 mg Retatrutide vial?: There is no single correct amount: water changes how many units a dose is, not how many doses the vial holds. With 1 mL the vial is 40 mg/mL and 7 mg is 17.5 units (0.18 mL) on a U-100 insulin syringe. The units table gives 1, 2, 5 mL.
How many doses are in a 40 mg Retatrutide vial?: 20 doses at 2 mg, 5 doses at 7 mg, 3 doses at 12 mg.
How long does a 40 mg Retatrutide vial last?: At 7 mg a dose and once weekly, about 5 weeks. How long a mixed vial keeps is a separate limit; see storage below.
How many 40 mg vials do I need for a 4-week run?: 1 vial at 2 mg 1 time a week for 4 weeks; 2 vials at 12 mg 1 time a week for 4 weeks.
What does 1 unit equal in a 40 mg Retatrutide vial?: 400 mcg with 1 mL, 200 mcg with 2 mL, 80 mcg with 5 mL of bacteriostatic water, on a U-100 syringe.

References (20 sources)

[1] IAPAM (International Association for Physicians in Aesthetic Medicine): 2 mg once weekly starting dose, step-up every 4 weeks to 4/9/12 mg maintenance (clinic, checked 2026-09-27)
[2] Peptide Dosing Protocols: Subcutaneous, once weekly, 2mg-4mg-6mg-9mg-12mg titration every 4 weeks (other, checked 2026-09-27)
[3] OpenStax, Rice University: 12.3 Preparing Unit-Dose Packaged Medications - Clinical Nursing Skills
[4] East Carolina University College of Nursing: Reconstitution of Medication
[5] Centers for Disease Control and Prevention: Considerations for Blood Glucose Monitoring and Insulin Administration
[6] DailyMed, National Library of Medicine: SEROSTIM (somatropin) for injection - prescribing information and instructions for use
[7] GenScript: Peptide Storage and Handling Guidelines
[8] DailyMed, National Library of Medicine: OZEMPIC (semaglutide) injection - prescribing information
[9] Centers for Disease Control and Prevention: Preventing Unsafe Injection Practices
[10] Pfizer: Bacteriostatic Water for Injection, USP - prescribing information
[11] OpenStax, Rice University: 12.5 Administering Subcutaneous Injections - Clinical Nursing Skills
[12] MedlinePlus, National Library of Medicine: Subcutaneous (SQ) injections
[13] Centers for Disease Control and Prevention: Chapter 6: Vaccine Administration - Pink Book
[14] US Food and Drug Administration: Best Way to Get Rid of Used Needles and Other Sharps
[15] US Food and Drug Administration: DOs and DON'Ts of Proper Sharps Disposal
[16] 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.
[17] 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.
[18] 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.
[19] 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.
[20] 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.