Retatrutide Side Effects: Dose-by-Dose Data from Phase 2 and Phase 3 Trials

Retatrutide's entire adverse-effect record is one phase 2 trial: 338 participants, 48 weeks, published in 2023. The phase 3 programme enrolling more than 5,800 people has published nothing. No regulator has approved a label, so no warnings section exists.

That makes retatrutide the clearest case in the weight loss and metabolic peptides category of a compound whose supply chain is better documented than its safety profile. For per-injection volume there is a retatrutide calculator. What follows reports what that one trial said, names every figure it did not publish, and refuses to fill the gaps with a class average.

Where does everything known about retatrutide's side effects come from?

Every reported adverse effect of retatrutide traces to Jastreboff et al., "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial," New England Journal of Medicine 2023;389(6):514-526, PMID 37366315. That trial randomised 338 participants for 48 weeks, double-blind and placebo-controlled. As of 11 August 2026, PubMed contains no phase 3 retatrutide results paper. Retatrutide is approved nowhere, so there is no label, no warnings section, no contraindications list and no boxed warning.

The second row is where most retatrutide safety content quietly goes wrong. A phase 3 programme existing is not the same as a phase 3 programme reporting, and a figure attributed to TRIUMPH-1 has been attributed to a trial that has published no results at all. The provenance of every circulating retatrutide number, including the efficacy ones, is traced in retatrutide and the 24.2% phase 2 figure, and where this compound sits against better-documented ones is in peptide side effects.

Nothing on this page is a dose recommendation. The amounts below are trial arms, and the only route to this compound that comes with a clinician attached is covered further down.

What did the phase 2 trial actually report about adverse effects?

The trial reported that adverse events were dose-related and gastrointestinal, and mostly mild to moderate. That is the characterisation the abstract gives, and it is the whole of it. No adverse-event percentages appear here because the abstract does not publish them, and no discontinuation rate is quoted because none is reported. What the trial did publish in detail is efficacy: −24.2% at 12 mg over 48 weeks against −2.1% on placebo.

At least 15% weight loss was achieved by 60% to 83% of participants across doses, against 2% on placebo. Read that against the adverse-effect column and the asymmetry is obvious: the efficacy result is broken out by dose to one decimal place, and the tolerability result is a phrase. Both come from the same 338 people.

"Dose-related" is the part worth holding onto, because it is the only quantitative shape the trial gives the adverse-effect data. It means the arms that produced the headline weight loss are also the arms that produced the most gastrointestinal burden, and the 12 mg figure that circulates as retatrutide's identity is the top of both curves.

Why is the unpublished discontinuation rate the most consequential gap?

Discontinuation is the figure that converts a symptom list into a tolerability judgment, and retatrutide's phase 2 abstract does not report one. Nausea affecting most participants means something entirely different if 3% stopped than if 20% did, and there is no way to tell which. Comparators publish theirs: tirzepatide ran 4.3%, 7.1% and 6.2% against 2.6% on placebo, semaglutide 4.5% for gastrointestinal reasons, and mazdutide 0.5% to 2.9%.

The reason this gap matters more than it sounds is structural rather than rhetorical. Every drug in this class shows its tolerability problem at scale, not in a 338-person study — dropout concentrates in broader populations, longer exposures and less-supervised escalation, all of which arrive in phase 3 and none of which a 48-week phase 2 tests. A four-trial programme enrolling more than 5,800 participants exists precisely to reveal that, and it has reported nothing.

There is a second-order effect worth naming. Because no retatrutide discontinuation figure exists, content about this compound tends to import one from tirzepatide or semaglutide, which is how a 4.3% figure measured in 2,539 people on a dual agonist ends up describing a triple agonist nobody counted. The tolerability record that does publish its numbers is in tirzepatide side effects and the SURMOUNT data.

What does glucagon receptor agonism add on top of an already emetogenic class?

Retatrutide is the only triple agonist here, adding glucagon receptor activity to the GIP and GLP-1 pairing tirzepatide uses. The glucagon component is intended to raise energy expenditure alongside appetite suppression, and it is also the component that adds nausea and vomiting risk on top of an already emetogenic class. That is a mechanistic expectation rather than a measured retatrutide finding, and the compounds sharing the glucagon lever do not reassure: survodutide produced gastrointestinal adverse events in 80.9% and 89.7% of participants.

The two glucagon-containing duals land at opposite ends of that column, which is the honest caveat to the mechanistic argument: mazdutide has the lowest discontinuation rate in the class and survodutide has the highest reported gastrointestinal burden, on an identical receptor pairing. Adding a glucagon lever does not deterministically produce a tolerability outcome, and anyone claiming it does is reasoning past the data.

What can be said is narrower and still useful. Retatrutide pulls three levers rather than two, the class's dose-limiting problem is gastrointestinal, and the compound with the most receptors has the least tolerability data. The class comparison in full is in retatrutide vs survodutide vs mazdutide.

Has the TRIUMPH phase 3 programme published any safety data?

No. TRIUMPH has published a design paper and no results. Giblin et al., Diabetes, Obesity and Metabolism, January 2026, PMID 41090431, describe four registrational trials enrolling more than 5,800 participants, with primary endpoints of percent body weight change, apnoea-hypopnoea index and WOMAC pain. Two further trials, NCT06383390 for cardiovascular and kidney outcomes and NCT06662383 against tirzepatide, are active and not recruiting. None has reported.

The consequence is absolute rather than partial. No weight-loss percentage, no adverse-event rate, no discontinuation figure and no durability figure can be attributed to any TRIUMPH trial, because none of them has published one. The 28% at 80 weeks figure in circulation traces to press reporting of a company statement in May 2026 that could not be verified against a primary source, and the 30.3% at 104 weeks figure has no source at all. Neither carries a safety dataset with it either. The programme is set out trial by trial in the TRIUMPH programme trial by trial.

How does retatrutide compare with the drugs that publish a discontinuation rate?

Retatrutide cannot be ranked on tolerability, because the metric that would rank it has not been published. Tirzepatide's SURMOUNT-1 discontinuation ran 4.3%, 7.1% and 6.2% against 2.6% on placebo across 2,539 participants over 72 weeks. Semaglutide's STEP 1 reported 44.2% nausea and 4.5% gastrointestinal discontinuation across 1,961. Mazdutide reports 0.5% to 2.9%. Retatrutide's comparable cell is empty, and an empty cell is not a low number.

Two of the five rows carry no discontinuation figure, which makes this a genuinely incomplete comparison rather than a close one. It is also worth noting what the comparison is not: cross-trial figures come from different populations, durations, escalation schedules and placebo responses, and none of these compounds has been tested head-to-head against retatrutide. The registered head-to-head, NCT06662383, is active and not recruiting.

What has been published about products sold as retatrutide outside trials?

Three 2026 publications bear on retatrutide outside the clinic, and the contents of none of them could be retrieved. The most directly relevant is Piatkowski, Craven, Cornell & Ferris, "Composition and Labelling Accuracy of Products Sold as Retatrutide in Australia," Drug and Alcohol Review, September 2026, DOI 10.1111/dar.70231, PMID 42559975. The citation is verified. The abstract could not be obtained, and its conclusions are therefore not characterised here — it is a source to read directly rather than one to summarise secondhand.

The Australian paper is the closest peer-reviewed analogue to the work this platform does, and anyone buying retatrutide should read it in the original. Naming a source without characterising it is a deliberate choice: a paper whose abstract could not be obtained can be pointed at, and the moment it is paraphrased from its title alone it becomes another unsourced figure of exactly the kind this page exists to flag.

Does fill variance change which side effects appear?

Fill quantity changes the dose without changing the vial, and on this platform retatrutide's measured quantity variance runs −4% to +22.5%, with most results within ±5%. Retatrutide is titrated in 1-2 mg steps, so a +22.5% overage is a step and a half nobody chose. The direction matters: an overfilled vial delivers more drug per unit than the label implies, and more drug in this class means more of the gastrointestinal effects that are dose-related by the trial's own description.

That table is arithmetic on a measured variance range, not a prediction about any particular vial. Its point is that the bottom row exceeds the highest amount ever given in the only trial that exists, and nothing about the powder, the solution or the syringe barrel reveals it. A symptom that follows is easy to attribute to the compound when it belongs to the quantity. How purity and net content answer different questions is in why 10 mg isn't 10 mg, and the arithmetic lives in the retatrutide injection guide.

Is there any route to retatrutide with a clinician attached?

One, and it does not run through a vendor. ClinicalTrials.gov lists NCT07629401, "Pre-approval Expanded Access of Retatrutide," with status AVAILABLE — expanded access, sometimes called compassionate use, operating through physicians and the sponsor. It is not approval. Retatrutide has never been approved anywhere, so it has never been in shortage, so no compounding pathway has ever existed for it, and material sold outside a trial or expanded access programme is an unapproved new drug.

That distinction is the practical safety point on this compound, because supervision is the variable that most changes what happens when an adverse effect appears. In a trial or an expanded access programme, someone is watching, recording and able to intervene. Outside one, a person experiencing dose-related vomiting on an unapproved triple agonist has no label to consult, no reported discontinuation rate to contextualise it and no prescriber who knows what was taken.

FDA's published position on this class applies directly: the agency "has warned companies that have illegally sold unapproved drugs... falsely labeled 'for research purposes' or 'not for human consumption.' These products have been sold directly to consumers for human use." On sport, retatrutide is not named on the WADA 2026 Prohibited List, but the S0 catch-all covers substances with no approval from any governmental regulatory health authority, expressly including drugs in clinical development — our reading of the plain text, not a published ruling. See do you need a prescription for retatrutide, compounding pharmacy versus research peptide and the FDA peptide regulation timeline.

Which retatrutide safety claims survive the evidence?

Two of the ten claims commonly made about retatrutide's safety hold up, and both are modest: that the phase 2 trial characterised adverse events as dose-related and gastrointestinal, and that expanded access exists through a physician. The claims that fail are the ones asserting a rate. No discontinuation figure has been published, no phase 3 safety data exist, no label exists, and a 99.67% purity average across 1,150 tests is not a safety finding.

What do 1,150 independent lab tests show, and what can they never show?

The Purity Index records retatrutide at 99.67% average across 1,150 independent tests (verified August 2026) — the largest test dataset on this platform — from Janoshik, Freedom Diagnostics, Bioviridian, Kovera and ILS, across 230 shops selling. Individual results run 99.52% to 99.98%, and quantity variance runs −4% to +22.5%. Those tests establish that vendors are broadly selling the correct molecule. They cannot establish an adverse-effect rate, a discontinuation rate or a long-term safety profile.

Retatrutide price data shows 15 shops in stock, median $8.00/mg, lowest $2.33/mg on a 40 mg vial (verified 31 July 2026), across 53 compared offers with vial prices from $24.99 to $500.00. By vial size, 5-10 mg runs a median $11.50/mg, 12-24 mg $8.23/mg and 30-65 mg $6.67/mg. Those figures exclude shipping, taxes and customs, coupon codes, bulk tiers, multi-vial kits and account-gated pricing.

Peptigrity's platform tracks 530 shops and 11,852 independent lab tests across 118 peptides, with 1,283 community reviews (verified August 2026), and trust scores weight community reviews and independently verified HPLC purity equally at 50% each. Set the compound-level figures against the evidence base and the imbalance is the finding: 1,150 independent lab tests of a drug with one published trial, no approval anywhere and no reported discontinuation rate. Endotoxin is the line most often missing on this compound, and an absent result means the batch was not tested rather than that it passed. Individual results are searchable in the lab test database, and vendor detail sits on the retatrutide compound page.

How do you check a retatrutide side-effect claim before believing it?

Six checks separate a retatrutide figure from a borrowed one, and the first is the one that eliminates most of them. Ask which trial produced the number, and whether that trial is the 338-person phase 2 — because it is the only one that has published. Then check whether a denominator and a placebo comparator are attached, whether the figure is a discontinuation rate that does not exist, and whether the vial itself has been verified for identity and quantity.

Identity is the check most people skip and the one that changes what a symptom means, because retatrutide and tirzepatide are 82 daltons apart and no HPLC purity figure addresses the difference. The full sourcing procedure is in where to buy retatrutide, and how to read an endotoxin result is in peptide endotoxin testing and LAL interpretation.

The trial that would settle this

Nothing about retatrutide tolerability is settled beyond 338 participants over 48 weeks, and the trial that would settle it already exists on paper. A phase 3 safety publication reporting discontinuation for adverse events at effective doses, against a placebo comparator, in a population broader than a phase 2 enrols would answer the central question in a single table. Four such trials are registered across more than 5,800 participants. None has published.

Frequently Asked Questions

Does retatrutide cause nausea?

The phase 2 trial described adverse events as dose-related and gastrointestinal, mostly mild to moderate, across 338 participants over 48 weeks. It did not publish a nausea percentage, so any specific figure quoted for retatrutide has been borrowed from another drug. Glucagon receptor agonism is expected to add nausea and vomiting risk on top of an already emetogenic class.

What is retatrutide's discontinuation rate?

Unknown. It is not reported in the phase 2 abstract, and no phase 3 trial has published. For scale, tirzepatide's SURMOUNT-1 discontinuation for adverse events ran 4.3%, 7.1% and 6.2% against 2.6% on placebo, and semaglutide's gastrointestinal discontinuation ran 4.5% in STEP 1. Neither figure describes retatrutide.

Is retatrutide better or worse tolerated than tirzepatide?

Nobody knows, and the trial designed to answer it has not reported. NCT06662383 is a registered head-to-head against tirzepatide, currently active and not recruiting. Retatrutide has more receptor targets, one published trial and no discontinuation rate; tirzepatide has an approved label, a 2,539-person phase 3 and a published rate.

Are there long-term safety data for retatrutide?

No. The longest published exposure is 48 weeks in 338 people. Nothing has been published beyond that duration, from any trial, and the four-trial phase 3 programme enrolling more than 5,800 participants has released no results of any kind.

Does a 99.67% purity average mean retatrutide is safe?

No. Across 1,150 independent lab tests, that figure establishes that vendors are broadly selling the correct molecule at roughly the stated quantity. Purity is a statement about proportion. It says nothing about adverse effects, dosing, long-term safety or how a phase 2 result holds up in phase 3.

What should someone do if symptoms appear?

Talk to a clinician, and say what was taken. That is not a formality on an unapproved compound: there is no label to consult, no published discontinuation rate to contextualise a symptom against, and severe or persistent vomiting, dehydration or severe abdominal pain need urgent medical assessment rather than a dose adjustment read off a forum.

Where this leaves retatrutide tolerability

Retatrutide is the compound where the gap between commercial documentation and clinical documentation is widest on this platform. 1,150 independent lab tests, 230 shops selling, 99.67% average purity — against one published trial of 338 people over 48 weeks that characterised adverse events in a phrase and published no discontinuation rate. The four-trial phase 3 programme built to fix that has released nothing.

What the trial did report is worth taking seriously rather than dismissing: adverse events were dose-related, gastrointestinal and mostly mild to moderate, in a double-blind placebo-controlled study published in the New England Journal of Medicine. That is a real result. It is also a phase 2 result, from a population smaller than any of the phase 3 comparators on this page, at a point in a drug's life when tolerability problems characteristically have not yet appeared.

The honest position is that retatrutide's efficacy is remarkable and its tolerability is undescribed, and that those two facts have to travel together. Anyone weighing this compound is weighing a −24.2% figure from 338 people against an adverse-effect record with no denominator in it, and the only route to it with a clinician attached is an expanded access programme reached through a physician.

Browse the weight loss and metabolic peptides category, or our complete peptide guide with 118 compounds (verified August 2026). For per-injection volume, use the retatrutide calculator alongside the reconstitution calculator. Compare shops through independent lab tests and community-verified shop reviews.

This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA (or equivalent regulators in your jurisdiction) for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.