How to Reconstitute Retatrutide (and Cagrilintide): What You Need to Know First

If you've searched for how to reconstitute retatrutide, you've probably noticed that most of the results come from websites selling it. That alone should make you pause. Before we get anywhere near vials and syringes, there's something you need to know, and we're putting it right at the top so nobody misses it.

Read This First: Retatrutide Is Not an Approved Drug

Retatrutide is an investigational medicine. It is not approved by the FDA for any use, and there is no legal prescription version you can pick up at a pharmacy. Eli Lilly, the company developing it, describes it as "investigational" in its own announcements, and it says it plans to submit an application to the FDA in the first quarter of 2027 (Lilly Q2 2026 results).

The FDA's position is blunt. It states that "Retatrutide and cagrilintide cannot be used in compounding under federal law," and that they "are not components of FDA-approved drugs and have not been found safe and effective for any condition" (FDA). The same page says the FDA has warned companies that illegally sold retatrutide and similar drugs "falsely labeled 'for research purposes' or 'not for human consumption.'"

So if someone is offering you a vial of retatrutide powder today, it isn't coming from a licensed pharmacy filling a lawful prescription. We don't recommend buying it, and nothing in this guide is a suggestion to use it. What this guide does is explain what retatrutide and cagrilintide are, where they stand, and how the reconstitution arithmetic works, so that if you're in a clinical trial or talking it through with a doctor, you understand the numbers.

What Is Retatrutide?

Retatrutide (also known by its development code LY3437943) is a once-weekly injectable peptide that Lilly calls a "first-in-class GIP, GLP-1, and glucagon triple hormone receptor agonist." In plain English, it acts on three hormone receptors involved in appetite, blood sugar, and energy use.

Think of it as the next step in a family tree. Semaglutide (Ozempic, Wegovy) acts on one receptor, GLP-1. Tirzepatide (Mounjaro, Zepbound) acts on two, GLP-1 and GIP. Retatrutide adds a third, the glucagon receptor.

Why Do People Call It "GLP-3"?

You'll see retatrutide nicknamed "GLP-3" online, and you'll see searches for "GLP-3 reconstitution." It's a catchy label, but it isn't a real scientific term. There's no hormone called GLP-3. The nickname seems to come from the idea that it's a "third generation" or "triple" drug. The accurate description is a triple agonist of the GIP, GLP-1, and glucagon receptors. If you see something sold as "GLP-3," treat that as a sign it's being marketed rather than prescribed.

Where Retatrutide Stands in 2026

Retatrutide has been through large Phase 3 trials, and the results have drawn plenty of attention. In May 2026, Lilly reported that in TRIUMPH-1, a trial in adults with obesity, people on the highest dose (12 mg) lost an average of 28.3% of their body weight at 80 weeks, compared with 2.2% on placebo (Lilly press release). Those figures use Lilly's efficacy estimand, which reflects people who stayed on treatment.

Side effects were common, especially digestive ones. Lilly reported nausea in 28.6%, 38.4%, and 42.4% of people on the 4 mg, 9 mg, and 12 mg doses versus 14.8% on placebo. Discontinuation due to side effects rose with dose, reaching 11.3% on 12 mg compared with 4.9% on placebo.

Trial participants didn't just get a vial and a dose. They started low and stepped up gradually under medical supervision, with regular monitoring. That's a big part of why trial results don't translate into instructions for anyone using retatrutide outside a trial.

Is There Any Legitimate Way to Get It?

Right now, the legitimate routes are clinical trials and, for a very narrow group, an expanded access program. Lilly lists a pre-approval expanded access program on ClinicalTrials.gov for adults with a BMI of 35 or more and at least two serious obesity-related complications who have exhausted approved treatments and can't join a trial. That's arranged through a treating physician, not ordered online.

If you're interested in retatrutide, the best step is talking to your doctor about approved options available today, like semaglutide or tirzepatide, and asking whether a clinical trial might be a fit.

What Is Cagrilintide?

Cagrilintide is a different kind of peptide. It's a long-acting analogue of amylin, a hormone released alongside insulin that helps with fullness and slows how fast your stomach empties. Novo Nordisk describes it as an "investigational" and "novel amylin analogue."

Cagrilintide is being developed mainly in combination with semaglutide, as a product called CagriSema. In December 2025, Novo Nordisk announced it had submitted CagriSema (cagrilintide 2.4 mg and semaglutide 2.4 mg, once weekly) to the FDA, reporting that in the REDEFINE 1 trial people lost 20.4% of their body weight at 68 weeks versus 3.0% on placebo (Novo Nordisk). The company said it expected the FDA to review the application in 2026. Check the FDA's website for the current status.

Here's the key point: even if CagriSema is approved, it's a single, ready-made combination injection made by the manufacturer. Standalone cagrilintide powder is not approved, and the FDA says it can't be used in compounding. Mixing your own cagrilintide and semaglutide is not the same thing as CagriSema.

How Reconstitution Math Works for Retatrutide Vials

With all of that said, here's the arithmetic. If you're in a trial or under a doctor's care, your study team or clinician will give you the exact instructions for your product. The math below is for understanding those instructions, not replacing them.

The formula is the same for every peptide. First, divide the milligrams in the vial by the millilitres of liquid added to get the concentration in mg/mL. Then divide the amount you were told to take by that concentration to get the volume in mL. On a U-100 insulin syringe, 100 units is 1 mL, so multiply the mL by 100 to get units.

This table shows the concentration for common vial sizes and diluent volumes, how many units hold 1 mg at that concentration, and how much is in 10 units.

Vial	Diluent added	Concentration	Units per 1 mg	mg in 10 units (0.1 mL)
5 mg	1 mL	5 mg/mL	20 units	0.5 mg
5 mg	2 mL	2.5 mg/mL	40 units	0.25 mg
5 mg	3 mL	1.667 mg/mL	60 units	0.167 mg
10 mg	1 mL	10 mg/mL	10 units	1 mg
10 mg	2 mL	5 mg/mL	20 units	0.5 mg
10 mg	3 mL	3.333 mg/mL	30 units	0.333 mg
15 mg	1 mL	15 mg/mL	6.67 units	1.5 mg
15 mg	2 mL	7.5 mg/mL	13.33 units	0.75 mg
15 mg	3 mL	5 mg/mL	20 units	0.5 mg
20 mg	1 mL	20 mg/mL	5 units	2 mg
20 mg	2 mL	10 mg/mL	10 units	1 mg
20 mg	3 mL	6.667 mg/mL	15 units	0.667 mg

Look at how much the numbers move. The same 10 units can hold very different amounts depending on how the vial was mixed. That's why the vial size alone never tells you how many units to draw.

Worked Example: A 10 mg Retatrutide Vial

Let's use 1 mg as a round example amount. It isn't a suggested dose. It just keeps the math easy to follow.

Say a 10 mg vial was mixed with 2 mL of diluent. The concentration is 10 ÷ 2 = 5 mg/mL. To get 1 mg, you'd need 1 ÷ 5 = 0.2 mL, which is 20 units on a U-100 syringe. At this concentration, every 1 mg takes 20 units.

Now say the same 10 mg vial was mixed with 1 mL instead. The concentration doubles to 10 mg/mL, and that same 1 mg is only 10 units. Same vial, same amount, half the units. Mix those two up and you've doubled the dose.

Worked Example: A 5 mg Retatrutide Vial

A 5 mg vial mixed with 1 mL gives 5 mg/mL. Mixed with 2 mL, it's 2.5 mg/mL, and 1 mg would be 40 units.

Here's a comparison that trips people up. At 10 units, a 5 mg vial in 2 mL holds 0.25 mg, a 10 mg vial in 2 mL holds 0.5 mg, and a 10 mg vial in 1 mL holds 1 mg. Same line on the syringe, very different amounts. If you ever switch vial sizes or diluent volumes, recalculate from scratch.

The FDA has already documented this kind of error with approved GLP-1 compounds, including patients who drew 50 units instead of 5 (FDA alert). With a drug that has no approved label at all, there's even less of a safety net. Our peptide calculator runs this math for any vial and diluent volume, and our peptide syringe units guide explains how to read the markings.

Cagrilintide Reconstitution Math

The same formula applies to cagrilintide. This table covers 5 mg and 10 mg vials.

Vial	Diluent added	Concentration	Units per 1 mg	mg in 10 units (0.1 mL)
5 mg	1 mL	5 mg/mL	20 units	0.5 mg
5 mg	2 mL	2.5 mg/mL	40 units	0.25 mg
5 mg	3 mL	1.667 mg/mL	60 units	0.167 mg
10 mg	1 mL	10 mg/mL	10 units	1 mg
10 mg	2 mL	5 mg/mL	20 units	0.5 mg
10 mg	3 mL	3.333 mg/mL	30 units	0.333 mg

For example, a 5 mg vial with 2 mL of diluent is 2.5 mg/mL, so each 1 mg takes 40 units.

Can You Mix Retatrutide and Cagrilintide in One Syringe?

We'd strongly advise against it. There's no approved product combining the two, and no published label telling you whether they're stable or compatible when mixed in a syringe or vial. Combining two unapproved peptides stacks two sets of unknowns. The only approved combination in this area, if the FDA approves it, will be CagriSema, which pairs cagrilintide with semaglutide in a manufacturer-made injection.

Mixing Technique and What to Watch For

If you're in a trial, follow the instructions your study team gives you. Some investigational products come in forms that don't need mixing at all.

The general principles for any reconstituted peptide are the same ones we cover in our guides to tirzepatide and semaglutide. Add the diluent slowly down the side of the vial, swirl or roll gently rather than shaking, and let any powder dissolve fully before you draw anything up.

The finished solution should be clear. If it's cloudy, has particles, or looks discoloured once the bubbles have settled, don't use it. Our guide to what to do with a cloudy peptide vial goes into this in detail. For an unapproved product with unknown quality controls, that rule matters even more.

How Long Does Mixed Retatrutide Last?

Nobody can give you a reliable answer, because there's no approved label. Approved GLP-1 products have tested storage limits printed on their labels. Retatrutide sold outside a trial has none.

As a general sterility rule, CDC injection safety guidance is to discard a punctured multi-dose vial after 28 days unless the manufacturer says otherwise. That's about keeping the vial sterile, not a promise that the peptide is still at full strength. If you're in a trial, your study team's storage instructions are the ones to follow.

Keep a Careful Record

If you're taking any peptide, trial medicine included, a clear record makes every conversation with your care team easier. Write down the vial size, how much diluent was added, the date you mixed it, the amount you took, and the units you drew. It also helps to note side effects, since digestive effects were common in the retatrutide trials.

PeptideKit lets you log each dose, set reminders, and keep notes alongside your protocol, and its built-in calculator shows the units for your exact vial so you can double-check your arithmetic every time.

Frequently Asked Questions

Is retatrutide FDA approved?

No. Retatrutide is an investigational drug. Lilly has said it plans to submit an application to the FDA in the first quarter of 2027. The FDA states that it has not been found safe and effective for any condition and can't be used in compounding.

What is GLP-3?

"GLP-3" is an informal nickname for retatrutide, not a real hormone or medical term. Retatrutide is a triple agonist that acts on the GIP, GLP-1, and glucagon receptors.

How do you reconstitute 10 mg of retatrutide?

There's no approved instruction for doing this outside a clinical trial, and we don't recommend using retatrutide outside one. As arithmetic only, 10 mg mixed with 2 mL gives 5 mg/mL, where each 1 mg is 20 units on a U-100 syringe. Mixed with 1 mL, it's 10 mg/mL.

How do you reconstitute 5 mg of retatrutide?

The same caution applies. As arithmetic only, 5 mg mixed with 1 mL gives 5 mg/mL, and mixed with 2 mL gives 2.5 mg/mL. The conversion tables above show the units for each.

Can compounding pharmacies make retatrutide?

No. The FDA says retatrutide and cagrilintide cannot be used in compounding under federal law. Products sold as "research use only" or "not for human consumption" aren't a legal substitute, and the FDA has warned companies selling them.

What is cagrilintide?

Cagrilintide is an investigational long-acting amylin analogue from Novo Nordisk. It's being developed mainly in combination with semaglutide as CagriSema, which was submitted to the FDA in December 2025. Standalone cagrilintide is not approved.

Can I mix retatrutide and cagrilintide together?

We don't recommend it. Neither is approved, and there's no published data on whether they're stable or compatible together. Combining two unapproved peptides adds risk without any label to guide you.

When will retatrutide be available?

Not before the FDA reviews and approves it. Lilly plans to submit its application in the first quarter of 2027, and FDA review takes months after that. Until then, clinical trials and Lilly's narrow expanded access program are the only legitimate routes.

The Bottom Line

Retatrutide has produced striking results in trials, but it's still an investigational drug with no FDA approval, no approved label, and no lawful compounded version. Cagrilintide is in the same position on its own, with its approved future most likely as part of Novo Nordisk's CagriSema combination.

If you're curious about retatrutide, talk to your doctor about approved options available today and whether a clinical trial could be right for you. If you're already in a trial, follow your study team's instructions, use the math above to understand them, and keep a careful record in PeptideKit so you have every detail ready for your next check-in.

Always consult with qualified healthcare professionals before starting any peptide therapy protocol. This information is for educational purposes only and does not constitute medical advice.