Retatrutide Long-Term Safety: The Short Answer

The longest data so far cover 80 weeks of treatment in Phase 3 trials, about 4,300 people on retatrutide across five trials, and 104 weeks in a selected group of TRIUMPH-1 participants. In TRIUMPH-1, the largest trial, published in full in September 2026, the 80-week safety numbers on the highest dose, 12 mg, were:

• Serious adverse events: 10.5% of participants, against 5.5% on placebo.
• Stopped because of adverse events: 11.2%, against 4.6% on placebo.
• Low blood pressure: 8.8%, against 0.9% on placebo, mostly mild or moderate.
• Most common side effects: gastrointestinal, with nausea in 42.4% against 14.8% on placebo, mostly while the dose was being increased.

In TRIUMPH-3, in people with established heart disease, major cardiovascular events were too few to show a difference from placebo either way (27 against 23). What happens over five or ten years, how often rare side effects occur, and whether retatrutide reduces heart attacks and strokes are not yet known; a dedicated outcomes trial with an enrollment goal of 10,000 people is due to run until 2029.

How Long Has Retatrutide Been Studied?

Based on how each trial was randomized, roughly 4,300 people received retatrutide across the five Phase 3 trials with results so far. That is enough to measure common side effects well, but trials of a few thousand people cannot reliably detect side effects that affect only one person in several thousand. Those usually come to light only after a drug has been used much more widely.

What the Longest Data Show

About 500 TRIUMPH-1 participants continued into an extension, according to the published paper; Lilly described the group as 532 participants who had a BMI of 35 or more when the trial began, completed the 80-week trial and tolerated their dose. They took retatrutide for another 24 weeks, escalating to the highest dose they tolerated, 9 mg or 12 mg. Lilly reported that they continued to lose weight: those originally assigned to 12 mg reached an average of 30.3% at 104 weeks if taken as intended, or 29.9% counting everyone in that group. Neither Lilly's announcement nor the published TRIUMPH-1 paper reports side effects for the extension separately, and because the group was selected, it cannot show how everyone in the trial would have fared.

In the Phase 3 trials, the most common adverse events were gastrointestinal. The share who stopped because of adverse events at 12 mg was 11.2% in TRIUMPH-1 (4.6% on placebo), according to the published paper, 7.7% in TRIUMPH-2 (4.9%) and 13.5% in TRIUMPH-3 (4.8%), all over 80 weeks, and 18.2% in the 68-week TRIUMPH-4 (4.0%), where Lilly said the rates were highly correlated with baseline BMI and included people who stopped because of perceived excessive weight loss.

The full TRIUMPH-1 paper gives the most complete safety picture so far for 80 weeks of treatment. Serious adverse events occurred in 7.7%, 7.7% and 10.5% of participants on 4 mg, 9 mg and 12 mg, against 5.5% on placebo. Low blood pressure was reported in 8.8% of participants on 12 mg against 0.9% on placebo, more often in people also taking blood pressure medicines, and was mostly mild or moderate (see retatrutide and blood pressure). Pancreatitis confirmed by adjudication occurred in 8 participants on retatrutide and 2 on placebo, numbers the investigators said were too small for conclusions about a treatment effect; severe or serious gallbladder or biliary disorders in 0.7% to 1.7% of participants on retatrutide, depending on the dose, and 0.7% on placebo; and cancer in 0.9% to 2.1%, against 1.0% on placebo. Three participants on 12 mg had severe or serious liver disorders: acute cholestatic hepatitis A, acute ischemic hepatitis most likely due to dehydration, and raised liver enzymes associated with worsening gallstone disease. Four participants on retatrutide and two on placebo died; one death, in a participant with known heart failure 189 days after stopping retatrutide, was adjudicated as cardiovascular.

TRIUMPH-3, in 1,949 people with a BMI of 35 or more and established cardiovascular disease, is the only Phase 3 announcement to report cardiovascular events. There were 27 major cardiovascular events — cardiovascular death, heart attack or stroke — among participants randomized to retatrutide and 23 among those randomized to placebo, a hazard ratio of 1.12 (95% confidence interval 0.64 to 1.96); on a broader measure that also counts death from any cause, heart failure events and coronary revascularization, there were 44 and 52 (hazard ratio 0.82, 0.55 to 1.22). The company said such events occurred less often than anticipated in both groups. With this few events, the results cannot show whether retatrutide raises or lowers cardiovascular risk. The TRIUMPH-1 paper also reports major cardiovascular events confirmed by adjudication, in 0.2% to 0.9% of participants on retatrutide, depending on the dose, and 0.2% on placebo; its investigators wrote that the trial was not powered to assess cardiovascular safety.

The 48-week Phase 2 obesity trial, published in full in 2023, found serious adverse events in 4% of participants on both retatrutide and placebo. One participant on 12 mg had acute pancreatitis and three on retatrutide had gallbladder events, and heart rate rose with the dose, peaking at 24 weeks and declining after that.

Warnings on Related Approved Drugs

Retatrutide has no label yet, so it has no official list of warnings. The approved drugs closest to it, semaglutide and tirzepatide, carry these on their US labels. An FDA review would decide which, if any, apply to retatrutide:

• Thyroid C-cell tumors. A boxed warning: both drugs cause these tumors in rodents, and whether they do in humans is unknown (see retatrutide and thyroid cancer risk). Both are contraindicated for people with a personal or family history of medullary thyroid carcinoma or with multiple endocrine neoplasia syndrome type 2.
• Acute pancreatitis and acute gallbladder disease.
• Low blood sugar, particularly in people with type 2 diabetes who also take insulin or medicines that increase insulin release.
• Acute kidney injury from dehydration, and severe gastrointestinal reactions.
• Diabetic retinopathy complications in people with type 2 diabetes.
• Hypersensitivity reactions and pulmonary aspiration during general anesthesia or deep sedation.
• Heart rate increase, a separate warning on semaglutide's label.

What Happens After Stopping Retatrutide?

Neither Lilly nor the published TRIUMPH-1 paper has reported what happens to weight after people stop retatrutide. The closest evidence comes from tirzepatide. In the SURMOUNT-4 trial, participants took tirzepatide for 36 weeks and were then assigned either to continue or to switch to placebo for a year. Those switched to placebo regained an average of 14.8% of their body weight over that year, and 13.5% of them kept at least 80% of the weight they had lost, against 93.4% of those who continued.

That is a different drug, and whether retatrutide behaves the same way has not been tested in a reported trial. The evidence on stopping is covered in more detail in weight regain after stopping retatrutide.

What Is Still Unknown

• Safety beyond two years. No reported trial has followed people on retatrutide for longer than 104 weeks.
• Rare side effects, which trials of a few thousand people cannot measure reliably.
• Cardiovascular outcomes. TRIUMPH-Outcomes, which is testing whether retatrutide lowers serious heart-related complications or prevents worsening kidney function, is expected to finish in February 2029.
• The course of dysesthesia. The company said the majority of cases resolved during treatment in most of its trials, but neither its announcements nor the TRIUMPH-1 paper say how long they lasted or what happened after people stopped.
• Weight after stopping retatrutide, and whether its effect holds over many years.

Why This Page Has No Monitoring Schedule

Some articles on this topic list tests to have, contraindications to observe and ways to taper the dose. This one does not. Retatrutide has no approved label, so there is no approved monitoring schedule, contraindication list or way of stopping it; for approved drugs, those come from the label and the prescriber.

Products sold online under the retatrutide name are not sold or supplied by Lilly. The company's retatrutide page (updated September 2026) says it is legally available only through its clinical trials; in August 2026 the company said it would also make it available to a limited number of patients who meet specific medical criteria and cannot join a trial. It warns that illicit products "may contain unknown ingredients, harmful contaminants and impurities." Nothing in the trial data describes what taking them for months or years might do.

Retatrutide Long-Term Safety in Summary

Retatrutide's safety has been studied for up to 80 weeks in Phase 3, and for 104 weeks in a selected group. In that time the common side effects were gastrointestinal; in the fully published TRIUMPH-1 trial, serious adverse events (10.5% against 5.5%) and low blood pressure (8.8% against 0.9%) were more common on the highest dose than on placebo; and cardiovascular events in people with heart disease were too few to show a difference either way. What happens over many years, how often rare side effects occur and what happens after stopping are not yet known; the TRIUMPH-Outcomes trial, expected to finish in 2029, is the next major source of long-term data.

Sources

• Eli Lilly. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. May 21, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials, delivering significant improvements in weight and A1C. July 23, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial. December 11, 2025.
• Eli Lilly. Lilly's triple agonist, retatrutide, demonstrated significant reductions in A1C and weight in first Phase 3 trial for treatment of type 2 diabetes. March 19, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, drove substantial improvements in weight, A1C, knee osteoarthritis pain, and obstructive sleep apnea, demonstrating its remarkable potential to treat obesity and its complications. June 6, 2026.
• Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med. Published September 29, 2026. DOI: 10.1056/NEJMoa2604169. (TRIUMPH-1)
• Eli Lilly. Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. September 29, 2026.
• Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514–526.
• Lilly Trials. The Effect of Retatrutide Once Weekly on Cardiovascular Outcomes and Kidney Outcomes in Adults (TRIUMPH-Outcomes). NCT06383390, trial listing.
• Novo Nordisk. Wegovy (semaglutide) US prescribing information, boxed warning and section 5. Revised June 2026.
• Eli Lilly. US prescribing information for tirzepatide for weight reduction, boxed warning and section 5. Revised August 2026.
• Eli Lilly. SURMOUNT-4 results announcement (tirzepatide). December 11, 2023.
• Eli Lilly. What to know about retatrutide. Last updated September 2026.
• STAT. Eli Lilly to allow more patients to apply for special access to unapproved obesity drug. August 3, 2026.

Medical Disclaimer: This article is for informational purposes only and is not medical advice. Retatrutide is investigational and is not approved by the FDA for any use. It is not available by prescription, and products sold online under its name are not sold or supplied by Lilly. Nothing here is a recommendation to use, seek out or avoid any medication.