Retatrutide's reported side effects are gastrointestinal, dose-related, mostly mild to moderate, and settle over time. In the phase 3 trial only 2 to 5% of patients stopped because of them, against 0% on placebo. That is a better tolerability signal than any approved drug in this class has posted. It is also all anyone has, because retatrutide is not approved and there is therefore no label and no incidence table.
What does not exist, and why that matters
For Wegovy or Zepbound you can read §6.1 of the prescribing information and find every adverse reaction that occurred in at least 2% or 5% of patients, by dose, with placebo alongside. That table is produced as part of approval.
Retatrutide has no label, so no such table exists. What exists is two trial publications describing the safety profile in prose, plus commentary in the literature. Any site presenting a percentage-by-dose table of retatrutide side effects has borrowed it from another drug or made it up, and this page will not do either.
What phase 2 reported
From the 2023 New England Journal of Medicine trial, 338 adults over 48 weeks:
- The most common adverse events were gastrointestinal.
- They were dose-related — more frequent at higher doses.
- They were mostly mild to moderate in severity.
- They were partially mitigated by a lower starting dose: beginning at 2 mg rather than 4 mg reduced them.
- There were dose-dependent increases in heart rate, peaking at 24 weeks and declining afterwards.
That last point deserves more attention than it usually gets. Heart rate increases are described across this drug class, but a specific dose-dependent rise that peaks and then falls is a distinct observation — and it is exactly what a 10,000-patient cardiovascular outcomes trial is designed to resolve.
The finding about the starting dose is the one that changed the programme: phase 3 escalates more gently than phase 2 did, because the trial showed that how you begin changes how it feels.
What phase 3 reported, and why it is the stronger evidence
TRANSCEND-T2D-1, published in the Lancet in June 2026, ran 537 adults with type 2 diabetes for 40 weeks. Its safety findings:
- Most frequent adverse events were generally mild to moderate gastrointestinal events, which subsided over time.
- 2 to 5% discontinued for adverse events, against 0% on placebo.
- No severe hypoglycaemia was reported — notable in a diabetes population.
- Two deaths occurred, both in the 4 mg group, both judged unrelated to the study drug.
- 91% of participants completed the treatment period on the study drug.
The discontinuation figure is the one to hold on to, because it is directly comparable with numbers the approved drugs publish.
| Drug | Stopped for adverse events | Setting |
|---|---|---|
| Retatrutide | 2–5% | Phase 3, 40 weeks, type 2 diabetes |
| Foundayo | 8% | Phase 3, 72 weeks |
| Zepbound | ~10% | Phase 3 with lifestyle lead-in |
| Semaglutide | ~7% | Phase 3, 68 weeks |
Different trials, different durations, different populations — so this is indicative rather than a ranking. But the strongest drug in the class having the lowest discontinuation rate is the same pattern tirzepatide showed against semaglutide in their head-to-head, and it contradicts the intuition that more powerful must mean harder to take.
One signal under discussion
A 2026 commentary in the European Journal of Internal Medicine examines a possible association between retatrutide and urinary tract infections, asking whether the timing of the reported cases explains them.
This is a question in the literature rather than an established adverse effect, and it is here because a page that reports only the reassuring findings is not a reference. Whether it survives scrutiny in the larger phase 3 population is unresolved.
What nobody knows yet
- Rare events. 338 people over 48 weeks and 537 over 40 weeks can show what is common. Neither can show what happens to one person in a thousand.
- Long-term effects. The longest published exposure is 48 weeks.
- Cardiovascular outcomes. The 10,000-patient trial has not reported. Given the heart rate finding, this is the most consequential gap.
- Whether the class warnings apply. Every approved GLP-1 carries a thyroid C-cell boxed warning from rodent studies, and pancreatitis and gallbladder warnings. Retatrutide has no label to carry them, but it is the same receptor family and there is no reason to assume it is exempt.
The side effects most people asking about this drug will actually get
This is the part that separates retatrutide from every drug on this site, and it is not about the molecule.
Nobody outside a trial or a narrow compassionate use programme is taking trial-dose retatrutide. What is being taken is bought online, and in 2026 a University of Queensland team analysed three such products, all labelled 10 mg. All three contained genuine retatrutide and the metals screen was clean. But the measured content was 51%, 165% and 190% of the label — a spread of nearly four-fold.
Set that against phase 2, where the adverse events were explicitly dose-related and where starting at 2 mg instead of 4 mg measurably reduced them. Someone measuring out what they believe is 4 mg from the weakest vial takes about 2 mg; from the strongest, about 7.6 mg. The trial's careful finding about starting doses cannot be applied to a product whose strength is unknown.
So the honest answer to "what side effects does retatrutide cause" has two halves. In trials: gastrointestinal, dose-related, and unusually well tolerated. Outside them: unknowable, because the dose is unknowable. The full analysis is in the retatrutide overview, and the regulatory picture in can you buy retatrutide.
Scientific References
4 sources- 1
Jastreboff AM, Kaplan LM, Frías JP, et al.
Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
New England Journal of Medicine · 389(6) · 2023PMID: 37366315
NEJM - 2
Bajaj HS, Welch M, Shah P, et al.
Efficacy and safety of retatrutide in people with type 2 diabetes (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial
The Lancet · 407(10546) · 2026PMID: 42250575
- 3
Koufakis T, Argyrakopoulou G, Kokkinos A, le Roux CW
Retatrutide and the urinary tract infection signal: Is the answer hidden in timing?
European Journal of Internal Medicine · 2026PMID: 42493254
- 4
Piatkowski T, Craven A, Cornell S, Ferris J
Composition and Labelling Accuracy of Products Sold as Retatrutide in Australia
Drug and Alcohol Review · 45(6) · 2026PMID: 42559975
NIH
References open in a new tab. Content is reviewed against peer-reviewed literature as part of our editorial policy.
About the author
Editor, Modern Weight Science
Claudiu Gheorghe is the editor of Modern Weight Science. He is not a physician. His role is to synthesize peer-reviewed studies, clinical-trial data, and FDA prescribing information into clear, plain-language explanations, and to make sure every factual claim on the site traces back to a cited source. Any decision about starting, changing, or stopping a medication belongs with a licensed clinician who knows your history.
Every claim is checked against peer-reviewed research through our review process and fact-checking policy.
Frequently Asked Questions
What are the side effects of retatrutide?
Gastrointestinal, dose-related, mostly mild to moderate, and settling over time — the standard profile for this drug class. The phase 2 trial also recorded dose-dependent increases in heart rate that peaked at 24 weeks and declined afterwards. There is no percentage-by-dose table, because retatrutide is not approved and therefore has no label.
Is retatrutide well tolerated?
On the published evidence, unusually so. In the phase 3 diabetes trial only 2 to 5% of patients discontinued because of adverse events, against 0% on placebo, and 91% completed the treatment period on drug. For comparison, Foundayo reports 8% and Zepbound roughly 10% in their own trials. These are separate trials rather than a head-to-head, but the direction is consistent.
Does retatrutide raise heart rate?
The phase 2 trial recorded dose-dependent increases in heart rate that peaked at 24 weeks and declined thereafter. Heart rate effects are described across this drug class, but this specific rise-and-fall pattern is a distinct observation. It is one of the questions the 10,000-patient cardiovascular outcomes trial is designed to settle, and that trial has not reported.
Why is there no table of retatrutide side effect percentages?
Because there is no label. Incidence tables by dose are produced as part of FDA approval, and retatrutide has not been approved anywhere. What exists is two trial publications describing the profile in prose. Any site showing a percentage-by-dose table for retatrutide has taken it from another drug or invented it.
Are the side effects the same for retatrutide bought online?
There is no way to know, because the dose is not known. Three products sold as retatrutide and labelled 10 mg were analysed in Australia in 2026 and contained 51%, 165% and 190% of their labelled content. Since the trial adverse events were explicitly dose-related — and since starting at 2 mg rather than 4 mg measurably reduced them — trial findings about dosing cannot be applied to a product whose strength varies nearly four-fold between vials.
Does retatrutide have a thyroid cancer warning?
It has no label, so it carries no formal warnings at all. Every approved GLP-1 receptor agonist carries a boxed warning for thyroid C-cell tumours based on rodent studies, along with pancreatitis and gallbladder warnings. Retatrutide acts on the same receptor family, and there is no evidence to suggest it is exempt — only an absence of the label that would say so.
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Not medical advice. This guide is for general education only. GLP-1 medications, dosing, and treatment suitability are decisions for you and a licensed clinician who knows your full medical history.