Retatrutide side effects: what the trials have reportedNot approved

Retatrutide is not approved. It’s an investigational drug made by Eli Lilly, and no regulator anywhere has approved it.¹ Retatrutide side effects are known only from clinical trials so far. In those trials, the most common problems were nausea, diarrhea and other stomach effects, much like approved GLP-1 medicines.^2,3,10

This guide covers what the Phase 2 and Phase 3 trials have reported. Several Phase 3 results so far come only from Lilly’s own announcements, and we say so where that’s the case. It doesn’t cover how to take retatrutide, because there is no approved dose.

Is retatrutide approved?

No. Lilly says retatrutide has not been approved by any regulatory agency.¹ It says no one should take anything claiming to be retatrutide outside a Lilly-sponsored trial.¹ The FDA says retatrutide cannot be used in compounding under federal law.⁴ The FDA has also warned telehealth companies for marketing it.⁴

Lilly says it plans to apply to the FDA for approval in the first three months of 2027.⁵ A plan to apply is not an approval, and the FDA’s review could take time. A large trial of heart and kidney outcomes, TRIUMPH-Outcomes, is still running.⁶

How is retatrutide different from Wegovy or Zepbound?

Retatrutide acts on three hormone targets: GLP-1, GIP and glucagon.² That’s why it’s sometimes called a “triple agonist.”

Acting on more targets doesn’t mean the side effects are already understood. Large trials are how researchers learn which effects are common and which are rare.

What side effects did people have in the trials?

Stomach side effects led every trial. The Phase 2 obesity trial, in 338 adults, found they were dose-related and mostly mild to moderate in severity.² The NEJM paper on TRIUMPH-1, a Phase 3 trial in 2,339 adults with obesity, also says The most common adverse events were gastrointestinal.³

Lilly reported the full list for TRIUMPH-1. On the 12 mg dose, nausea affected 42.4% of people, compared with 14.8% on placebo.⁷ Diarrhea affected 32.0% compared with 13.5%, and vomiting 25.3% compared with 4.8%.⁷

Side effect	Share of people, medicine then placebo
Nausea	Medicine 42.4%Placebo 14.8%
Diarrhea	Medicine 32%Placebo 13.5%
Constipation	Medicine 26.1%Placebo 10.9%
Vomiting	Medicine 25.3%Placebo 4.8%
Dysesthesia	Medicine 12.5%Placebo 0.9%
Urinary infection	Medicine 8.4%Placebo 5.3%

Share of adults with each side effect on retatrutide 12 mg or placebo over 80 weeks in TRIUMPH-1, a trial in adults with obesity without diabetes. Figures are from Lilly's announcement of the results. Dysesthesia means skin that feels tingly, burning or extra sensitive.⁷

The trial lasted 80 weeks and tested three doses: 4 mg, 9 mg and 12 mg.³ We name these doses only to explain the trial results. They are not a guide for anyone.

Does the dose make a difference?

Yes. In TRIUMPH-1, nausea rose from 28.6% on 4 mg to 38.4% on 9 mg and 42.4% on 12 mg.⁷ Vomiting rose from 10.6% to 22.8% and 25.3%, compared with 4.8% on placebo.⁷

The starting dose mattered too. In the Phase 2 trial, stomach side effects were partially mitigated with a lower starting dose.² In the trial’s posted results, 21 of 35 people (60%) who started the 8 mg arm at a higher first dose had nausea.⁸ Of 35 who started the same arm at a lower first dose, 6 (17%) had nausea, compared with 8 of 70 (11%) on placebo.⁸

What is dysesthesia, and how often did it happen?

Dysesthesia is skin that feels different: tingling, burning, prickling or extra sensitive to touch. It showed up more often than on placebo in each of these Phase 3 trials.

• TRIUMPH-1. It affected 12.5% on 12 mg, compared with 0.9% on placebo, as reported by Lilly.⁷
• TRIUMPH-4. This trial was in adults with knee arthritis. Lilly reported dysesthesia in 20.9% on 12 mg, compared with 0.7% on placebo.⁹
• TRIUMPH-2. In adults with type 2 diabetes, the Lancet paper reports 7% on 12 mg, compared with 1% on placebo.¹⁰

Lilly says these events were generally mild to moderate, that most went away during treatment, and that most people kept taking retatrutide.⁷ The sources we checked don’t explain why it happens. If your skin feels strange during a trial, tell your study team.

How many people stopped because of side effects?

It depended on the trial and the dose. In TRIUMPH-1, 11.3% on 12 mg stopped because of side effects, compared with 4.9% on placebo.⁷ On 4 mg, it was 4.1%, close to placebo.⁷

TRIUMPH-4 had the highest rate. There, 18.2% on 12 mg stopped because of side effects, compared with 4.0% on placebo.⁹ Lilly says these rates were highly correlated with baseline BMI and included people who stopped because they felt they had lost too much weight.⁹

Are side effects different with diabetes or heart disease?

The pattern looks similar, though the numbers differ by trial. In a Phase 2 trial of 281 adults with type 2 diabetes, mild to moderate stomach side effects affected 35% on retatrutide.¹¹ That compared with 13% on placebo and 35% on dulaglutide (Trulicity), an approved GLP-1 medicine. The paper reports no reports of severe hypoglycaemia and no deaths during the study.¹¹

TRIUMPH-2 tested retatrutide in 1,152 adults with obesity and type 2 diabetes for 80 weeks.¹⁰ On 12 mg, nausea affected 28% and diarrhea 34%, compared with 8% and 13% on placebo.¹⁰

TRIUMPH-3 enrolled adults with severe obesity and heart disease. Lilly reported nausea in 22.4% on 12 mg, compared with 5.8% on placebo.¹² In that trial, 13.5% on 12 mg stopped because of side effects, compared with 4.8% on placebo.¹²

What other effects have been reported?

• Heart rate. In the Phase 2 trial, heart rate rose with dose. It peaked at 24 weeks and declined thereafter.²
• Low blood pressure. In TRIUMPH-2, low blood pressure affected 6% on 12 mg, compared with under 1% on placebo.¹⁰
• Urinary tract infections. In TRIUMPH-1, they affected 8.4% on 12 mg, compared with 5.3% on placebo.⁷

What about serious side effects?

The data here are still thin. The Phase 2 obesity trial posted its results on ClinicalTrials.gov. Serious events of any kind affected 10 of 267 people on retatrutide (3.7%), compared with 3 of 70 on placebo (4.3%).⁸ They included one case of acute pancreatitis and one of acute gallbladder inflammation, both on retatrutide.⁸

In TRIUMPH-2, six people on retatrutide and one on placebo died. The trial investigators judged that none of these deaths were related to the study drug.¹⁰ The Phase 3 sources we could check don’t give overall serious-event rates, or rates of pancreatitis or gallbladder disease.

What are the risks of retatrutide sold online?

Products sold online as retatrutide are not the trial drug. Lilly warns that illicit products may contain unknown ingredients, harmful contaminants and impurities, or the wrong amount of drug.¹ The FDA has warned companies selling retatrutide that was falsely labeled for research purposes or not for human consumption.⁴

A 2026 study looked at Reddit posts from 7,823 people who said they used unapproved retatrutide.¹³ The most common complaints were increased appetite (17.1%), tiredness (15.2%) and nausea (11.6%). The authors say this kind of study cannot assess incidence, causality, dose-response, or comparative safety.¹³

A 2026 case report describes a woman in her mid-20s who was admitted to hospital with 5 days of nausea and vomiting.¹⁴ She had received 4 weekly injections of an unverified product said to contain retatrutide. Her symptoms cleared within a week.¹⁴

If you’ve used one of these products, tell your doctor what you took and when. Bring the vial or packaging if you still have it.