Peptide guide

Retatrutide

An investigational triple-hormone-receptor agonist (GLP-1, GIP, and glucagon) from Eli Lilly, studied for obesity and metabolic disease.

Retatrutide is an experimental once-weekly injectable that hits three metabolic receptors at once, developed by Eli Lilly and still working through clinical trials. Unlike most compounds in this catalog, it has real human data behind it: phase 2 showed up to 24% body-weight loss at 48 weeks, and a phase 3 obesity trial reported up to 28% at 80 weeks. It is not FDA-approved, and its long-term safety is still unestablished. People are sourcing research-grade versions ahead of approval, so the practical questions are how to handle it correctly, what the trial doses actually were, and how not to get scammed buying it.

By the Zapify Research team

Reviewed against 9 clinical & research sources · Updated June 2026 · Educational use only

Type: Triple agonistGLP-1 / GIP / glucagon
Route: Subcutaneousonce weekly
Typical dose: 2–12 mg/wktitrated up
Cycle: Titrate & maintain16–20 wks to top dose
Storage: Mixed: ~4 wksSealed: months
Status: Not FDA-approved

What is Retatrutide?

An investigational Eli Lilly injectable (LY3437943) that hits GLP-1, GIP, and the glucagon receptor at once — not FDA-approved, with long-term safety unestablished.

Retatrutide is an investigational drug, known in the lab as LY3437943, that Eli Lilly is developing for obesity and related metabolic disease. It's a single engineered molecule, a peptide with a fatty-acid chain attached to make it last longer in the body, given as a once-weekly injection under the skin.

What sets it apart is that it activates three receptors at once. GLP-1 and GIP are the two gut hormones behind drugs like semaglutide and tirzepatide; they curb appetite and improve how the body handles blood sugar. Retatrutide adds a third target, the glucagon receptor, which nudges the body to burn more energy and helps clear fat from the liver. Hitting all three is the reason its weight-loss numbers in trials have run higher than the drugs already on the market.

This is a different situation from most compounds people buy as research peptides. Retatrutide isn't a fringe molecule with only animal data; it's a serious pharmaceutical candidate that has produced strong results in large human trials. It simply hasn't finished the road to approval yet.

Retatrutide isn't FDA-approved. It's still in clinical trials, with phase 3 obesity data only reported in 2026 and a regulatory filing expected no earlier than late 2026. There is no approved version you can be prescribed, and its long-term safety hasn't been established. Anything sold as retatrutide today is unapproved research material, not a finished medicine.

What is it studied for?

Unusually, the headline evidence is human: published phase 2 and phase 3 obesity trials, with the gaps being completed readouts, long-term safety, and approval.

Retatrutide is unusual for this catalog in that the headline evidence comes from people, not rats. It has run through phase 2 and into phase 3 trials in humans, published in journals like the New England Journal of Medicine, with the trials built around obesity and metabolic disease rather than recovery or longevity. The data is real and it is substantial. What's missing is the finish line: completed phase 3 readouts across every indication, long-term safety, and approval.

Evidence base, by stage

SeveralCompleted human trials (phase 1–2)

None yetCompleted phase 3 / approval

The research has clustered in three areas:

Obesity & weight lossThe flagship use. Phase 2 reached about 24% body-weight loss at 48 weeks on the top dose; phase 3 reported up to roughly 28–30% over longer follow-up.

Type 2 diabetesStudied for blood-sugar control, where the GLP-1 and GIP arms of the molecule do much of the work, alongside weight reduction.

Fatty liver diseaseA phase 2a trial in MASLD (formerly NAFLD) showed liver fat dropping by more than 80% at the higher doses, driven largely by the glucagon arm.

The mechanism is better understood here than with most experimental compounds, because each of the three receptors is already well studied on its own. GLP-1 and GIP suppress appetite and improve insulin response; glucagon raises energy expenditure and mobilizes liver fat. What's still being worked out is the long game: how the three effects balance over years, what the glucagon component does to heart rate and metabolism with extended use, and where the right dose sits for safety rather than just for scale numbers.

Why people use it

People want the highest published weight-loss numbers in the class and won't wait years, but the version sold has no regulator-approved quality control and no medical monitoring.

Most people reaching for retatrutide before approval are doing it for one reason: the trial weight-loss numbers are the highest published for any drug in this class, and they don't want to wait two or three years for a pharmacy version. These are the situations that pull people in, not a guarantee the results transfer outside a controlled trial:

Obesity or stubborn weight that hasn't moved with diet, training, or even an approved GLP-1 drug, and wanting the strongest option reported so far.
Already familiar with semaglutide or tirzepatide and chasing the larger effect a triple agonist showed in trials.
Metabolic markers like fatty liver or blood sugar, where the phase 2 data looked striking.
Frustration with the cost or wait of approved options, and a willingness to use research material in the gap before retatrutide is on the market.

Retatrutide isn't approved, the version you'd buy hasn't been through any quality control a regulator signed off on, and the trial results came from supervised dosing with medical monitoring you won't have at home. That's the weight against it. The case for curiosity is also real: this is one of the few compounds in this space with strong, peer-reviewed human efficacy data behind it, a mechanism that makes sense receptor by receptor, and a side-effect pattern that so far looks like the GLP-1 drugs already in wide use. Worth understanding closely. Not worth treating as settled or self-managing without a clinician.

How to reconstitute Retatrutide

Mix with bacteriostatic water, swirl don't shake; a 10 mg vial in 1 mL gives 10 mg/mL, so 10 units is 1 mg — and titration makes the draw math matter at each step.

Research-grade retatrutide arrives as a small puck of dry powder in a sealed vial. Before it can be drawn into a syringe, it has to be mixed into liquid. That step is called reconstitution, and it's the same process used across injectable peptides.

Step 1Start with powderWipe the rubber stopper with an alcohol swab.

Step 2Add bac. waterRun it slowly down the inside wall — never shake.

Step 3Draw your doseThe calculator gives the exact units to draw to.

Wipe the rubber stopper with an alcohol swab first, every time.
Use bacteriostatic water, not plain sterile water and not saline. The trace of benzyl alcohol in it holds back bacteria, which matters because a weekly drug means you'll be drawing from the same vial for weeks.
Add the water slowly, running it down the inside glass wall. Don't blast it straight onto the powder.
Don't shake it. Swirl gently and let it dissolve on its own. Shaking foams the solution and can damage the peptide.

A common setup is a 10 mg vial mixed with 1 mL of bacteriostatic water, which gives 10 mg/mL. On a U-100 insulin syringe, 10 units is then 1 mg and 20 units is 2 mg, which lines up with a typical starting dose. The water doesn't change how much drug is in the vial; it only sets the concentration, which decides how many units you draw for a given milligram dose. Because retatrutide is titrated upward over months, getting that draw math right at each step matters more here than with a fixed-dose peptide.

Calculate your exact Retatrutide reconstitution →

Dose & units

No approved dose; trials titrated weekly injections up to 12 mg, climbing 2→4→6→9→12 mg about every four weeks, reaching the top dose in roughly 16–20 weeks.

There is no FDA-approved dose for retatrutide, because the drug isn't approved at all. Every number below is a dose used in a published clinical trial, run under medical supervision, not a self-administration instruction. The trials titrated slowly for a reason: jumping ahead drives the side effects up sharply. Decide what goes into your body with a licensed provider, not with this page.

Trial dose range

Phase 2 tested weekly doses of 1, 2, 4, 8, and 12 mg, with the strongest weight-loss results at 8 and 12 mg. Phase 3 settled on a range topping out at 12 mg per week. Everything is dosed in milligrams once a week, given subcutaneously.

Titration

Retatrutide is started low and stepped up gradually, which is central to how it's used rather than optional. The phase 3 schedule began everyone at 2 mg and climbed 2 → 4 → 6 → 9 → 12 mg, raising the dose roughly every four weeks so the body adjusts before the next step. Reaching the top dose takes around 16 to 20 weeks. Starting low and moving slowly is what keeps the nausea and other gut effects manageable.

Maintenance

Unlike a recovery peptide run as a short cycle, retatrutide in trials is taken continuously once the target dose is reached, in the same way approved weight-loss drugs are ongoing rather than time-limited. Trial participants stayed on it for 80 weeks and beyond. What happens to the weight after stopping wasn't the focus, and with the GLP-1 drugs already approved, much of it tends to return once the drug is discontinued.

Titrate up~16–20 weeks

Maintainongoing

For the exact mark to draw to on your insulin syringe at each step of a titration, don't eyeball it. The calculator turns your vial size, water, and target milligram dose into the precise number of units.

Get your exact units →

Storage

Sealed powder is stable for months at room temperature; once mixed, refrigerate at 2–8 °C and use within about 4 weeks — a sterility limit, not potency.

Sealed & dryDry powder stays stable for months at room temperature and tolerates shipping heat.

ReconstitutedRefrigerate at 2–8 °C in the main compartment, use within about 4 weeks, don't freeze, keep out of light, and toss if cloudy or discolored.

You'll see longer windows quoted for peptide vials. Those figures are beyond-use dates for a sealed, unmixed vial that a compounding pharmacy has stability-tested, and they stop applying the moment you add water. A mixed vial runs on the roughly four-week clock instead, because that's how long the preservative in bacteriostatic water reliably keeps the solution clean once you're drawing from it.

That four-week limit is about sterility, not potency — the molecule itself often stays good well beyond it. Reconstitute with plain sterile water instead of bacteriostatic and you drop to a day or two, since there's no preservative holding bacteria back.

Don't freeze a reconstituted vial, keep it out of direct light, write the mix date on the label, and throw it out if the solution ever turns cloudy or discolored, whatever the date says.

Side effects & safety

Mostly GI effects during escalation, with nausea up to ~60% at 12 mg and resting heart rate rising 5–10 bpm; class warnings cover pancreatitis, gallbladder, and a rodent thyroid-tumor signal.

Retatrutide's side-effect picture is better documented than almost anything else in this catalog, because it comes from controlled human trials rather than anecdote. The pattern looks like the GLP-1 drugs already in use: mostly gastrointestinal, mostly during dose escalation, mostly mild to moderate. They were also common, and they were the main reason people dropped out of the trials.

Most common: nausea, vomiting, diarrhea, and constipation, worst while the dose is climbing. Nausea rose sharply with dose, reported by roughly 14% at the lowest dose and up to about 60% at 12 mg in phase 2.
A rise in resting heart rate of roughly 5–10 beats per minute, peaking around week 24 and easing after.
Reduced appetite and early fullness, which is part of how it works but can shade into not eating enough.
Discontinuation from side effects ran around 6–16% in the retatrutide groups, versus none on placebo.

This is a powerful metabolic drug, not a recovery peptide, and the cautions are real. The heart-rate increase matters if you have a cardiac condition. The appetite suppression can be severe enough to cause dehydration or muscle loss without attention to protein and fluids. GLP-1 drugs as a class carry warnings around pancreatitis, gallbladder problems, and a thyroid-tumor signal seen in rodents. None of this should be managed alone. If you have heart disease, a history of pancreatitis or thyroid cancer, or you're pregnant or breastfeeding, this isn't a compound to experiment with.

If you compete, treat retatrutide as prohibited. Because it has no regulatory approval anywhere, it is captured by the WADA Prohibited List as a non-approved substance (category S0), banned at all times — that classification alone makes a positive test a doping violation. Worth knowing the nuance: approved GLP-1 drugs like semaglutide and tirzepatide are currently on WADA's monitoring program rather than the banned list, so it isn't the GLP-1 mechanism itself that prohibits retatrutide — it's that the drug is still investigational.

And the biggest risk with research-grade material isn't even the drug's known effects. It's whether what's in the vial is actually retatrutide, at the strength on the label. That comes down to where you buy it.

How to vet a source

With a complex engineered molecule, a sloppy synthesis hides in white powder, so insist on a batch-specific, third-party COA whose lot number matches your vial.

Because retatrutide isn't approved, every gram sold outside a trial comes from the unregulated research-chemical market, and a real share of independently tested vials come back underdosed, impure, or not even the compound on the label. With a complex engineered molecule like this one, a sloppy synthesis is easy to hide in a white powder, and you can't see it. Where you buy matters more than almost anything else here. The one document that separates a real seller from a gamble is a certificate of analysis: a third-party lab's report on what's actually in the vial.

A real COA shows

An identity test (usually mass spectrometry) confirming the peptide is what the label says.
A purity figure from HPLC, typically 98% or higher.
A lot or batch number that matches the number printed on your vial.
A named, independent accredited lab and a recent test date.

Walk away if

There’s no COA, or it’s a generic image with no lot number.
The “certificate” comes from the seller instead of a third-party lab.
The lot number doesn’t match your vial, or there isn’t one at all.
It’s a flat image you can’t trace back to the lab that issued it.

That's the standard worth holding any seller to, ours included. Ask for the batch-specific COA before you buy, match the lot number to your vial, and don't accept a screenshot in place of a traceable report.

See the Zapify compound catalog →

Common questions about Retatrutide

Is retatrutide approved or proven to work in people?

It works in people, but it isn't approved. This is the rare compound in this space with strong human data: phase 2 showed up to about 24% body-weight loss at 48 weeks, and a 2026 phase 3 obesity trial reported up to roughly 28–30% over longer follow-up. What it doesn't have yet is FDA approval, completed phase 3 readouts across every indication, or established long-term safety. A regulatory filing isn't expected before late 2026, so anything sold now is unapproved research material.

How is retatrutide different from semaglutide or tirzepatide?

It hits more receptors. Semaglutide (Ozempic, Wegovy) is a single GLP-1 agonist. Tirzepatide (Mounjaro, Zepbound) is a dual GLP-1 and GIP agonist. Retatrutide adds a third target, the glucagon receptor, which raises energy expenditure and clears liver fat. That third arm is the leading explanation for why its trial weight-loss numbers ran higher than either approved drug. It's also why it isn't interchangeable with them on dose or side-effect profile.

Why does retatrutide have to be titrated so slowly?

Because the gut side effects scale with dose and with how fast you climb. Nausea, vomiting, and diarrhea were the most common adverse events in trials, concentrated during dose escalation, and the most frequent reason people quit. The trials stepped the dose up roughly every four weeks for a reason. Starting at the top would mean a much rougher ride and a higher chance of giving up entirely.

Will the weight come back if I stop?

Probably much of it, based on how the rest of this drug class behaves. Retatrutide in trials is taken continuously rather than as a short course, and with approved GLP-1 drugs, weight tends to return after stopping because the appetite suppression that drove the loss goes away. Retatrutide's own off-drug data is limited, but there's no reason to expect it to behave differently. It's an ongoing treatment, not a cycle you finish.

Why bacteriostatic water and not saline or sterile water?

Because retatrutide is a weekly drug, so you're drawing from the same vial across weeks. Bacteriostatic water carries a trace of benzyl alcohol that holds back bacteria between draws; plain sterile water and saline have no preservative. On a multi-dose vial you'll keep for a month, the professional sources all point the same way: bacteriostatic.

References

This page is for research and educational purposes only. It is not medical advice or a recommendation to use any compound. The dose ranges shown are reported by clinics and research literature, not validated medical standards, and Retatrutide is not FDA-approved. Talk to a licensed medical provider about anything you put in your body.