Where to Buy GLP-3 (Retatrutide): Vendor Guide and What GLP-3 Actually Means

If you have been searching for "GLP-3," you are almost certainly looking for retatrutide. Here is the uncomfortable truth that most vendor pages will not tell you: there is no such thing as a GLP-3 receptor. The name is grey market marketing shorthand, invented to imply a next generation beyond GLP-1 drugs and GLP-1/GIP dual agonists. This guide decodes the naming confusion, then walks through exactly how to evaluate a source, what a legitimate certificate of analysis must show, and how purity math changes the dose actually delivered to your research model.

Research-use disclaimer: Retatrutide (LY3437943) is an investigational compound developed by Eli Lilly. It is not approved by the FDA or any regulatory agency for human use. Nothing here is medical advice or a purchasing recommendation. This article documents what the published literature and product documentation report, for educational and laboratory-reference purposes only.

"GLP-3" Does Not Exist: What You Are Actually Buying

The human body has receptors for GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. There is no fourth incretin called GLP-3 and no GLP-3 receptor anywhere in human physiology. The term was coined in the grey market to sell retatrutide by suggesting it is the "third generation" of GLP drugs.

The logic vendors are gesturing at is real even though the label is fake:

• Generation 1: semaglutide, a GLP-1 mono-agonist
• Generation 2: tirzepatide, a GLP-1 plus GIP dual agonist
• Generation 3: retatrutide, a GLP-1 plus GIP plus glucagon triple agonist

Someone reading that sequence quickly and marketing it might mangle "third generation GLP drug" into "GLP-3." It sticks because it sounds like a receptor and it sounds newer. But the technically correct description of retatrutide is a single-molecule triple agonist of the GIP, GLP-1, and glucagon receptors. If a vendor sells you a "GLP-3 receptor agonist," they are describing a receptor that does not exist. That alone tells you how much pharmacology they actually understand.

The practical problem: people searching "GLP-3" often do not know they are buying retatrutide, which means they cannot cross-check trial data, dosing, or safety. Clearing up the name is the first step to sourcing safely. If you want the deeper mechanism and trial breakdown, see our triple agonist research explainer and the Learn hub.

Decoding Vendor Labels: Grey Market Names to Actual Compound

Vendors use a rotating set of nicknames, partly for search traffic and partly to stay ambiguous. This table translates every common label back to the one compound they all refer to.

The single most useful heuristic: a serious source will name retatrutide or LY3437943 somewhere in the listing. A source that only ever says "GLP-3" and never once writes "retatrutide" is a red flag, because it suggests they are selling a search term rather than a documented compound.

What Legitimate Retatrutide Documentation Must Show

A certificate of analysis (COA) is the single most important document when evaluating any research peptide source. For retatrutide specifically, a legitimate COA must include every one of the following. Missing any one is a reason to walk away.

The batch-matching requirement deserves emphasis. A generic COA that a vendor reuses for every order is nearly worthless, because it does not correspond to the vial in your hand. The chain you want is: your vial's batch number, printed on the COA, tested by a named lab, on a recent date. Break any link in that chain and the document proves nothing.

For a broader sourcing framework beyond retatrutide, our vendor directory and the companion where to buy retatrutide guide apply the same standards across sources.

Typical Vial Sizes and Price per Milligram

Retatrutide is generally sold as lyophilized (freeze-dried) powder in single-dose vials. Because it is investigational and unapproved, there is no official pricing, and grey market prices vary widely with batch, source, and quantity. The ranges below describe what the market typically looks like rather than any recommendation.

The consistent pattern across the grey market is that price per mg falls as vial size rises, the standard bulk-discount curve. That creates a trap: the lowest price per mg is not automatically the best value, because a larger vial requires more reconstituted product to be stored and used before degradation. Use the calculator to convert a vial size and reconstitution volume into a concrete per-dose cost before comparing sources.

Cost per Research Month, Worked Across Dose Levels

The Phase 2 obesity trial (Jastreboff AM et al., New England Journal of Medicine, 2023) escalated weekly subcutaneous doses through 1, 4, 8, and 12 mg arms. Reproducing that escalation on paper shows how monthly compound consumption scales, which is the number that actually drives cost.

Assume a standard once-weekly schedule (four doses per research month, consistent with the terminal half-life of about 6 days that supports weekly dosing):

The key insight competitors gloss over: cost scales linearly with dose, but weight-loss response in the trial did not. Weight change at 48 weeks was placebo -2.1%, 1 mg -8.7%, 4 mg -17.1%, 8 mg -22.8%, and 12 mg -24.2%. Going from 8 mg to 12 mg raises monthly compound consumption by 50% (32 mg to 48 mg) for an additional 1.4 percentage points of weight change in the trial (-22.8% to -24.2%). The jump from 1 mg to 4 mg, by contrast, quadrupled consumption but nearly doubled the effect (-8.7% to -17.1%). The steepest efficiency is in the lower-to-middle range; the top of the curve costs far more per marginal percentage point.

A realistic escalation does not sit at one dose all month. A trial-style ramp might spend several weeks each at 1, 2, and 4 mg before reaching a maintenance dose, so early research months consume far less compound than steady-state months at 8 mg or 12 mg. Model your own schedule in the calculator and track actual consumption in the tracker rather than assuming a flat monthly figure.

Purity Math: Why 95% Versus 99% Changes the Delivered Dose

This is the section most vendor pages omit entirely, and it is where the money actually is. Purity is not a vanity metric. It directly determines how much retatrutide is in the dose you draw up.

Consider a vial labeled 10 mg of retatrutide:

The gap between 99% and 95% purity is 4 percentage points, which sounds trivial. But on a nominal 12 mg dose, that is the difference between roughly 11.88 mg and 11.40 mg of actual retatrutide, about 0.48 mg lost per dose. Over a four-dose research month that compounds, and over a full escalation it can shift where a model actually lands on the dose-response curve documented in the trials.

Two further points make purity matter even more than the arithmetic suggests:

• The missing percentage is not empty space. At 95% purity, 5% of the mass is synthesis byproducts, deletion sequences, or residual solvents, some of which have their own biological activity and none of which are characterized on a grey market COA.
• Purity claims are only as trustworthy as the batch-matched, third party COA behind them. A "99% purity" banner with no supporting document is a number, not a measurement. Always tie the claim back to the COA chain described above.

This is why the HPLC purity target of 98%+ is not arbitrary. It is the threshold below which byproduct load and dose error both climb quickly.

Vendor Evaluation Criteria

Score any prospective source against these criteria before anything else. This framework is compound-agnostic but tuned to retatrutide's specific risks.

The pricing criterion is counterintuitive but important. Prices far below the market range are not a bargain; they are a warning. Retatrutide is expensive to synthesize correctly at high purity. A price that undercuts everyone else usually means underfilled vials, low purity, or substitution with a cheaper GLP-1 peptide that will still register as "something" on a crude test.

Red Flags Checklist

Treat any single item here as a reason to slow down and any two as a reason to walk away:

• The listing uses "GLP-3" or "triple G" branding but never once names retatrutide or LY3437943
• No batch-specific COA, or a COA that does not match the batch number on your vial
• Purity is claimed but there is no mass spectrometry confirming the molecule is actually retatrutide
• Prices are dramatically below the market per-mg range
• No reconstitution or storage instructions are provided
• The testing lab is unnamed, or testing is described as "in-house"
• The COA date predates the batch, or no date is given at all

For the safety side of the equation, our complete side effects guide documents the dose-dependent gastrointestinal profile, and the results timeline covers how the numbers unfold over the 48-week trial window. If you are new to evaluating research peptides at all, the quiz is a quick way to test your sourcing literacy.

What the Research Actually Documents

To keep the sourcing conversation grounded in real data rather than grey market hype, here is what the peer-reviewed literature reports about retatrutide.

• Obesity Phase 2 (Jastreboff AM et al., NEJM 2023): n=338 adults with obesity over 48 weeks. Weight change was placebo -2.1%, 1 mg -8.7%, 4 mg -17.1%, 8 mg -22.8%, 12 mg -24.2%. At 24 weeks the 12 mg arm was already near -17.5%. All participants in the 8 mg and 12 mg arms reached at least 5% weight loss at 48 weeks, and roughly 26% of the 12 mg arm reached at least 30% weight loss.
• Type 2 diabetes Phase 2 (Rosenstock J et al., The Lancet 2023): n=281 over 36 weeks. HbA1c fell up to -2.02% at 12 mg, versus -0.01% for placebo and -1.41% for dulaglutide 1.5 mg. Weight loss reached up to -16.94% at 12 mg.
• Liver fat substudy (2023): liver fat content was reduced by up to about 86% at 24 weeks in participants with MASLD, and about 80% reached normal liver fat content (under 5%).
• Pharmacokinetics: terminal half-life of about 6 days supports once-weekly dosing, with Tmax roughly 24 to 48 hours.
• Safety: adverse events were predominantly gastrointestinal (nausea, diarrhea, vomiting, constipation), dose dependent, mostly mild to moderate, and worst during escalation. Discontinuation due to adverse events ran roughly 6 to 16% across dose arms. A dose-dependent heart rate increase peaked around 24 weeks then declined.

The Phase 3 program, called TRIUMPH (TRIUMPH-1 through TRIUMPH-4 plus a cardiovascular outcomes study), is ongoing. Until those read out, every figure above comes from Phase 2, and retatrutide remains investigational.

Frequently Asked Questions

Is GLP-3 a real drug?

No. GLP-3 is a grey market nickname, not a real receptor or a distinct compound. There is no GLP-3 receptor in human physiology. When a vendor sells "GLP-3," they are selling retatrutide (LY3437943), a triple agonist of the GIP, GLP-1, and glucagon receptors.

What is the difference between GLP-3, Triple G, and Reta?

They all refer to the same compound, retatrutide. "Reta" is a normal abbreviation, "Triple G" is informal slang for its triple GIP/GLP-1/glucagon mechanism, and "GLP-3" is inaccurate marketing shorthand implying a generation beyond dual agonists. Only "retatrutide" and "LY3437943" are precise identifiers.

What purity should a retatrutide COA show?

Look for an HPLC purity target of 98% or higher, ideally 99%, accompanied by mass spectrometry confirming the molecule's identity. Purity below that threshold means more synthesis byproducts and a lower effective delivered dose. The claim only counts if it is backed by a batch-specific, third party COA with a recent test date.

Why are some retatrutide vials so much cheaper?

Prices far below the market per-mg range are a warning sign, not a deal. Retatrutide is costly to synthesize at high purity, so unusually low prices often indicate underfilled vials, low purity, or substitution with a cheaper GLP-1 peptide. Cheap sourcing frequently costs more once you account for the reduced actual compound content.

How do I verify a COA is legitimate?

Confirm the batch or lot number on the COA matches your vial, that a named independent third party lab performed the testing, and that the test date is recent and after the batch was made. A generic COA reused across all orders, or one from a different batch, does not describe the vial you received and proves nothing about it.

How much retatrutide does a research month use?

On a once-weekly schedule, a month is four doses, so a steady 12 mg dose consumes 48 mg per month, 8 mg consumes 32 mg, and 4 mg consumes 16 mg. Real escalation schedules start lower and ramp up, so early months use far less. Model your specific schedule in the calculator.

Is retatrutide approved or legal to buy?

Retatrutide is investigational and not approved by the FDA or any regulatory agency for human use. It is sold only as a research chemical, and its Phase 3 TRIUMPH program is still ongoing. Treat all sourcing as laboratory-reference research rather than a consumer purchase.

Key Research Citations

For continued reading, compare the generations directly on the semaglutide and tirzepatide pages, review the full retatrutide profile, and see the benefits and research evidence guide.