Side effects
Retatrutide side effects: trial rates by dose
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Short answer
As of October 19, 2026, gastrointestinal effects were the most common retatrutide side effects in trials. In TRIUMPH-1 (80 weeks), nausea affected 42.4% on 12 mg versus 14.8% on placebo, and 11.3% versus 4.9% stopped treatment because of adverse events. Dysesthesia, an abnormal skin sensation, reached 20.9% on 12 mg in TRIUMPH-4.
On this page13 sections
- Retatrutide side effects at a glance
- TRIUMPH-1 adverse events by dose (80 weeks)
- TRIUMPH-2 adverse events: obesity with type 2 diabetes (80 weeks)
- TRIUMPH-3 and TRIUMPH-4 adverse events
- TRANSCEND-T2D-1 adverse events (40 weeks)
- Dysesthesia: the signal to know about
- Starting dose and stomach side effects: Phase 2 evidence
- Heart rate
- Why some people stopped treatment
- What is not yet published in full
- Safety outside the trials
- FAQ
- Sources
| Item | Value | Source |
|---|---|---|
| TRIUMPH-1 nausea, 4 / 9 / 12 mg vs placebo | 28.6% / 38.4% / 42.4% vs 14.8% (80 weeks) | Eli Lilly, May 21, 2026 |
| TRIUMPH-1 vomiting, 4 / 9 / 12 mg vs placebo | 10.6% / 22.8% / 25.3% vs 4.8% | Eli Lilly, May 21, 2026 |
| TRIUMPH-1 stopped for adverse events | 4.1% / 6.9% / 11.3% vs 4.9% | Eli Lilly, May 21, 2026 |
| TRIUMPH-1 dysesthesia | 5.1% / 12.3% / 12.5% vs 0.9% | Eli Lilly, May 21, 2026 |
| TRIUMPH-4 dysesthesia, 9 / 12 mg vs placebo | 8.8% / 20.9% vs 0.7% (68 weeks) | Eli Lilly, Dec 11, 2025 |
| TRIUMPH-4 stopped for adverse events | 12.2% / 18.2% vs 4.0% | Eli Lilly, Dec 11, 2025 |
| TRIUMPH-2 hypotension, 4 / 9 / 12 mg vs placebo | 1% / 5% / 6% vs under 1% | The Lancet, Sep 29, 2026 |
| Phase 2 nausea, 8 mg arm by starting dose | 60.0% (4 mg start) vs 17.1% (2 mg start) | ClinicalTrials.gov, Sep 13, 2023 |
| Phase 2 heart rate | Dose-dependent increases peaked at 24 weeks, then declined | N Engl J Med, Jun 26, 2023 |
Also useful: Retatrutide level plotter.
Retatrutide side effects at a glance
Every rate on this page is the share of trial participants who reported an adverse event during the trial, as published by Lilly or in a journal or registry. Retatrutide is investigational and these rates come from supervised trials with a gradual dose step-up. More on the drug is on the retatrutide hub.
| Trial (weeks) | Nausea | Diarrhea | Vomiting | Dysesthesia | Stopped for adverse events |
|---|---|---|---|---|---|
| TRIUMPH-1 (80) | 42.4% vs 14.8% | 32.0% vs 13.5% | 25.3% vs 4.8% | 12.5% vs 0.9% | 11.3% vs 4.9% |
| TRIUMPH-2 (80) | 28.0% vs 8.0% | 33.6% vs 13.2% | 15.7% vs 4.2% | 7.3% vs 0.7% | 7.7% vs 4.9% |
| TRIUMPH-3 (80) | 22.4% vs 5.8% | 24.4% vs 8.7% | Not reported | 6.4% vs 1.3% | 13.5% vs 4.8% |
| TRIUMPH-4 (68) | 43.2% vs 10.7% | 33.1% vs 13.4% | 20.9% vs 0.0% | 20.9% vs 0.7% | 18.2% vs 4.0% |
| TRANSCEND-T2D-1 (40) | 26.5% vs 3.7% | 22.8% vs 4.5% | 17.6% vs 2.2% | 4.4% vs 0% | 5.1% vs 0% |
The trials differ in who they enrolled, how long they ran and how events were collected, so a higher rate in one row does not prove the drug is less tolerable in that population. Compare arms within a trial, not across trials.
All Phase 3 arms started at 2 mg once weekly and stepped up every 4 weeks to the target dose. (Eli Lilly, Dec 11, 2025) The titration tool shows those published schedules, and the retatrutide plotter models how the relative amount of drug builds up over the step-up. Neither is dosing guidance.
TRIUMPH-1 adverse events by dose (80 weeks)
TRIUMPH-1 is the largest trial, with 2,339 adults without diabetes randomized to 4, 9 or 12 mg or placebo. (Eli Lilly, May 21, 2026)
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhea | 25.2% | 34.1% | 32.0% | 13.5% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Upper respiratory infection | 14.2% | 12.2% | 13.1% | 11.6% |
| Dysesthesia | 5.1% | 12.3% | 12.5% | 0.9% |
| Urinary tract infection | 7.5% | 8.8% | 8.4% | 5.3% |
| Stopped for adverse events | 4.1% | 6.9% | 11.3% | 4.9% |
The pattern is dose-related for nausea, vomiting and dysesthesia. On 4 mg, the adverse-event discontinuation rate (4.1%) was close to placebo (4.9%).
TRIUMPH-2 adverse events: obesity with type 2 diabetes (80 weeks)
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Diarrhea | 27.4% | 33.5% | 33.6% | 13.2% |
| Nausea | 13.7% | 20.8% | 28.0% | 8.0% |
| Constipation | 14.0% | 16.2% | 16.8% | 9.4% |
| Decreased appetite | 5.8% | 12.3% | 17.1% | 4.5% |
| Vomiting | 5.5% | 10.2% | 15.7% | 4.2% |
| Dysesthesia | 4.5% | 5.6% | 7.3% | 0.7% |
| Urinary tract infection | 3.8% | 6.3% | 8.0% | 6.6% |
| Hypotension (Lancet) | 1% | 5% | 6% | Under 1% |
| Stopped for adverse events | 3.8% | 11.6% | 7.7% | 4.9% |
Hypotension means low blood pressure. The Lancet paper reports that hypotension and dysesthesia were more frequent with retatrutide than placebo. It also reports deaths of 2, 3 and 1 participants on 4, 9 and 12 mg versus 1 on placebo, all judged by investigators to be unrelated to the study drug. (The Lancet, Sep 29, 2026)
In this trial the 9 mg arm stopped for adverse events more often (11.6%) than the 12 mg arm (7.7%). The Lancet uses a slightly different definition, permanent discontinuation due to adverse events or death, and reports 4%, 12% and 8% versus 5%. Both sources show the same 9 mg pattern.
TRIUMPH-3 and TRIUMPH-4 adverse events
TRIUMPH-3 enrolled 1,949 adults with a BMI of 35 or more and cardiovascular disease and tested only 9 and 12 mg. TRIUMPH-4 enrolled 445 adults with knee osteoarthritis and also tested 9 and 12 mg. (Eli Lilly, Jul 23, 2026) (Eli Lilly, Dec 11, 2025)
| Event | TRIUMPH-3, 9 / 12 mg | TRIUMPH-3 placebo | TRIUMPH-4, 9 / 12 mg | TRIUMPH-4 placebo |
|---|---|---|---|---|
| Nausea | 21.7% / 22.4% | 5.8% | 38.1% / 43.2% | 10.7% |
| Diarrhea | 30.1% / 24.4% | 8.7% | 34.7% / 33.1% | 13.4% |
| Constipation | 18.0% / 15.7% | 7.1% | 21.8% / 25.0% | 8.7% |
| Vomiting | Not reported | Not reported | 20.4% / 20.9% | 0.0% |
| Decreased appetite | 13.5% / 14.5% | 3.0% | 19.0% / 18.2% | 9.4% |
| Dysesthesia | 6.4% / 6.4% | 1.3% | 8.8% / 20.9% | 0.7% |
| Stopped for adverse events | 9.8% / 13.5% | 4.8% | 12.2% / 18.2% | 4.0% |
TRIUMPH-3 also reported urinary tract infections in 6.1% and 7.0% versus 5.3%, and hyperglycemia (high blood sugar) in 3.9% and 3.1% versus 13.4% on placebo.
TRANSCEND-T2D-1 adverse events (40 weeks)
TRANSCEND-T2D-1 enrolled 537 adults with type 2 diabetes managed by diet and exercise. (Eli Lilly, Mar 19, 2026)
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 16.4% | 19.5% | 26.5% | 3.7% |
| Diarrhea | 18.7% | 26.3% | 22.8% | 4.5% |
| Vomiting | 15.7% | 15.0% | 17.6% | 2.2% |
| Dysesthesia | 4.5% | 2.3% | 4.4% | 0% |
| Stopped for adverse events | 2.2% | 4.5% | 5.1% | 0% |
Dysesthesia: the signal to know about
Dysesthesia is an abnormal or unpleasant skin sensation. It is not a side effect typically associated with GLP-1 drugs, and it appeared in every retatrutide Phase 3 trial reported so far. The highest rate was 20.9% on 12 mg in TRIUMPH-4, against 0.7% on placebo. (Eli Lilly, Dec 11, 2025) In TRIUMPH-1 it rose from 5.1% on 4 mg to 12.5% on 12 mg. (Eli Lilly, May 21, 2026) The sources we reviewed do not report how long episodes lasted or how many were severe.
Starting dose and stomach side effects: Phase 2 evidence
The Phase 2 obesity trial tested the same 8 mg target dose with two different starting doses. The NEJM paper reported that gastrointestinal events were dose-related, mostly mild to moderate, and partly reduced by starting at 2 mg instead of 4 mg. (N Engl J Med, Jun 26, 2023) The registry counts make the difference concrete.
| Arm (starting dose) | Nausea | Vomiting |
|---|---|---|
| Placebo | 8/70 (11.4%) | 1/70 (1.4%) |
| 1 mg | 10/69 (14.5%) | 2/69 (2.9%) |
| 4 mg (2 mg start) | 6/33 (18.2%) | 4/33 (12.1%) |
| 4 mg (4 mg start) | 12/33 (36.4%) | 4/33 (12.1%) |
| 8 mg (2 mg start) | 6/35 (17.1%) | 2/35 (5.7%) |
| 8 mg (4 mg start) | 21/35 (60.0%) | 9/35 (25.7%) |
| 12 mg (2 mg start) | 28/62 (45.2%) | 12/62 (19.4%) |
Percentages are calculated from the posted counts. This registry table lists only events reported by 5% or more of an arm, so it may not match the journal’s own percentages. The arms were small, so treat single-arm differences with caution. Phase 3 then used a 2 mg start for every arm.
In the Phase 2 type 2 diabetes trial, mild-to-moderate gastrointestinal events occurred in 35% of participants across the retatrutide groups, ranging from 13% on 0.5 mg to 50% in the 8 mg fast-escalation group, versus 13% on placebo. (The Lancet, Jun 26, 2023)
Heart rate
The Phase 2 obesity paper reported dose-dependent increases in heart rate that peaked at 24 weeks and declined afterward. (N Engl J Med, Jun 26, 2023) We have not found Phase 3 heart-rate figures in the releases or abstracts we reviewed, so we do not give a number.
Why some people stopped treatment
Adverse-event discontinuation on 12 mg ranged from 5.1% (TRANSCEND-T2D-1) to 18.2% (TRIUMPH-4). Lilly said TRIUMPH-4 discontinuations included people who stopped because of perceived excessive weight loss, and that rates were lower in people with a baseline BMI of 35 or more: 8.8% and 12.1% on 9 and 12 mg versus 4.8% on placebo. (Eli Lilly, Dec 11, 2025) Efficacy results for every trial are in the trial results guide.
What is not yet published in full
- Full Phase 3 safety tables. Our TRIUMPH-1 rates come from Lilly’s release; we reviewed only the abstract of the NEJM paper. (N Engl J Med, Sep 29, 2026)
- Serious adverse events by category. Category-level serious event rates are not in the sources we reviewed.
- TRIUMPH-3 vomiting. Not reported in Lilly’s July 23, 2026 release.
- Phase 3 heart rate and blood pressure beyond the TRIUMPH-2 hypotension figures.
- Registry results. No Phase 3 trial had posted results on ClinicalTrials.gov as of October 19, 2026.
- Long-term safety. The longest placebo-controlled data run 80 weeks.
Safety outside the trials
In the trials, participants report symptoms to the study investigators, who record and assess them. That system does not exist for products sold online. Lilly has said no retatrutide medicine is approved anywhere. (Eli Lilly, Aug 12, 2026) Anyone who has used an unapproved product sold as retatrutide and has severe or persistent symptoms should seek medical care and tell the clinician what was used. See whether retatrutide is FDA approved for the regulatory details.
Frequently asked questions
What are the side effects of retatrutide?
- In the Phase 3 trials, the most common were nausea, diarrhea, constipation, vomiting and decreased appetite, and they were more frequent at higher doses. In TRIUMPH-1, nausea affected 28.6%, 38.4% and 42.4% on 4, 9 and 12 mg versus 14.8% on placebo, per Lilly's May 21, 2026 release. Dysesthesia, an abnormal skin sensation, was also more common than on placebo.
What are reta side effects at 12 mg?
- In TRIUMPH-1, the 12 mg arm reported nausea 42.4%, diarrhea 32.0%, constipation 26.1%, vomiting 25.3% and dysesthesia 12.5%, and 11.3% stopped treatment because of adverse events, versus 4.9% on placebo. In TRIUMPH-4, 12 mg dysesthesia was 20.9% and adverse-event discontinuation 18.2%. These are trial rates over 68 to 80 weeks.
What is dysesthesia on retatrutide?
- Dysesthesia is an abnormal or unpleasant skin sensation. It is a signal seen with retatrutide that is not typical of GLP-1 drugs. Lilly reported it in 12.5% on 12 mg versus 0.9% on placebo in TRIUMPH-1 and 20.9% versus 0.7% in TRIUMPH-4. The releases we reviewed do not describe its duration or severity in detail.
Does retatrutide raise heart rate?
- In the Phase 2 obesity trial published in NEJM in 2023, retatrutide caused dose-dependent increases in heart rate that peaked at 24 weeks and declined afterward. Phase 3 heart-rate figures were not included in the Lilly releases or journal abstracts we reviewed as of October 19, 2026.
How many people stopped retatrutide because of side effects?
- It varied by trial and dose. Adverse-event discontinuation on 12 mg was 11.3% in TRIUMPH-1, 7.7% in TRIUMPH-2, 13.5% in TRIUMPH-3, 18.2% in TRIUMPH-4 and 5.1% in TRANSCEND-T2D-1. Placebo rates ranged from 0% to 4.9%. In TRIUMPH-4, Lilly said discontinuations included people who perceived their weight loss as excessive.
Sources
- Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. Eli Lilly and Company (via PR Newswire; also investor.lilly.com), May 21, 2026. Accessed Oct 19, 2026.
- Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. Eli Lilly and Company (via PR Newswire; also investor.lilly.com), Sep 29, 2026. Accessed Oct 19, 2026.
- Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. The Lancet 2026;408(10563):1455-1472 (abstract via PubMed PMID 42810372; doi:10.1016/S0140-6736(26)01861-1), Sep 29, 2026. Accessed Oct 19, 2026.
- Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials, delivering significant improvements in weight and A1C. Eli Lilly and Company (via PR Newswire), Jul 23, 2026. Accessed Oct 19, 2026.
- 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. Eli Lilly and Company (via PR Newswire), Dec 11, 2025. Accessed Oct 19, 2026.
- Lilly's triple agonist, retatrutide, demonstrated significant reductions in A1C and weight in first Phase 3 trial for treatment of type 2 diabetes. Eli Lilly and Company (via PR Newswire), Mar 19, 2026. Accessed Oct 19, 2026.
- A Study of LY3437943 in Participants Who Have Obesity or Are Overweight (NCT04881760) - registry record with posted results. ClinicalTrials.gov (U.S. NLM), Sep 13, 2023. Accessed Oct 19, 2026.
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med 2023;389(6):514-526 (abstract via PubMed PMID 37366315; doi:10.1056/NEJMoa2301972), Jun 26, 2023. Accessed Oct 19, 2026.
- Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. The Lancet 2023;402(10401):529-544 (abstract via PubMed PMID 37385280; doi:10.1016/S0140-6736(23)01053-X), Jun 26, 2023. Accessed Oct 19, 2026.
- Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med (abstract via PubMed PMID 42814954; doi:10.1056/NEJMoa2604169), Sep 29, 2026. Accessed Oct 19, 2026.
- Lilly calls on online platforms, payment companies and regulators to shut down the illegal retatrutide black market. Eli Lilly and Company (via PR Newswire), Aug 12, 2026. Accessed Oct 19, 2026.