The most common retatrutide side effects in the phase 3 trials were nausea, diarrhoea, constipation and vomiting (Lilly, May 2026). In TRIUMPH-4, up to 20.9% reported dysesthesia, an unusual skin sensation, against 0.7% on placebo (Lilly, December 2025). Retatrutide and orforglipron are not registered in Singapore, and GetLean does not prescribe or supply them. GetLean does prescribe and supply HSA-registered GLP-1 medications, after a consultation with Dr Quek, with daily WhatsApp coaching between reviews.
Each of those four digestive effects was more frequent than on placebo. Across the four TRIUMPH trials, between 3.8% and 18.2% of participants stopped treatment because of side effects, depending on the trial and dose, against 4.0% to 4.9% on placebo (Lilly, May 2026; Lilly, July 2026; Lilly, December 2025). Most figures here are Lilly's announced topline results; TRIUMPH-1 and TRIUMPH-2 have since been published, in the New England Journal of Medicine and The Lancet (Jastreboff 2026; Bellido 2026).
Availability in Singapore. This is an investigational medicine. It is not registered with Singapore's Health Sciences Authority, and it has no approved application with the United States Food and Drug Administration either, so it cannot be prescribed in either country. Outside clinical trials, Lilly releases it only through a pre-approval expanded access programme for a small group of adults with severe obesity who cannot join a trial, on their own doctor's request and where Lilly makes it available, and anything offered for sale under this name is not what the trials studied.
Education only. This page is general education about a medicine that is not registered in Singapore. It is not an advertisement or an offer. GetLean does not prescribe or supply retatrutide, and nothing here recommends using it.
Dysesthesia: an abnormal, unpleasant sensation in the skin, such as tingling or burning, without an obvious outside cause.
TRIUMPH-1: adults without diabetes
TRIUMPH-1 followed 2,339 adults with obesity or overweight and a weight-related condition, without diabetes, for 80 weeks (Lilly, May 2026).
| Reported by | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhoea | 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% |
| Dysesthesia | 5.1% | 12.3% | 12.5% | 0.9% |
| Urinary tract infection | 7.5% | 8.8% | 8.4% | 5.3% |
| Stopped because of side effects | 4.1% | 6.9% | 11.3% | 4.9% |
Source: Lilly, May 2026.
Lilly describes the types of side effects as generally consistent with trials of other medicines in the same family. It says dysesthesia and urinary tract infections were generally mild to moderate, that most resolved during treatment, and that most participants continued taking retatrutide (Lilly, May 2026). At 4 mg, fewer people stopped because of side effects than on placebo; at 12 mg, more than twice as many did. Retatrutide vs Mounjaro side effects sets these figures beside those from Mounjaro's main trial.
TRIUMPH-2 and TRIUMPH-3: diabetes and heart disease
TRIUMPH-2 enrolled 1,152 adults with type 2 diabetes and obesity or overweight. TRIUMPH-3 enrolled 1,949 adults with a BMI of 35 or above and established cardiovascular disease, and tested 9 mg and 12 mg only (Lilly, July 2026).
| Reported by | TRIUMPH-2: 4 / 9 / 12 mg | Placebo | TRIUMPH-3: 9 / 12 mg | Placebo |
|---|---|---|---|---|
| Diarrhoea | 27.4% / 33.5% / 33.6% | 13.2% | 30.1% / 24.4% | 8.7% |
| Nausea | 13.7% / 20.8% / 28.0% | 8.0% | 21.7% / 22.4% | 5.8% |
| Dysesthesia | 4.5% / 5.6% / 7.3% | 0.7% | 6.4% / 6.4% | 1.3% |
| Stopped because of side effects | 3.8% / 11.6% / 7.7% | 4.9% | 9.8% / 13.5% | 4.8% |
Source: Lilly, July 2026.
Dysesthesia was less common in these two trials than in TRIUMPH-1, though still several times the placebo rate. At 12 mg, the share stopping because of side effects was higher in TRIUMPH-3, at 13.5%, than in TRIUMPH-2, at 7.7% (Lilly, July 2026). The published TRIUMPH-2 paper reports the same pattern, and adds low blood pressure in 1% to 6% on retatrutide against under 1% on placebo (Bellido 2026).
TRIUMPH-4: knee osteoarthritis
TRIUMPH-4, which reported in December 2025, followed 445 adults with obesity or overweight and knee osteoarthritis for 68 weeks on 9 mg, 12 mg or placebo (Lilly, December 2025).
| Reported by | 9 mg | 12 mg | Placebo |
|---|---|---|---|
| Nausea | 38.1% | 43.2% | 10.7% |
| Diarrhoea | 34.7% | 33.1% | 13.4% |
| Constipation | 21.8% | 25.0% | 8.7% |
| Vomiting | 20.4% | 20.9% | 0.0% |
| Dysesthesia | 8.8% | 20.9% | 0.7% |
| Stopped because of side effects | 12.2% | 18.2% | 4.0% |
Source: Lilly, December 2025.
These are the highest rates of dysesthesia and of stopping so far. Lilly says the dysesthesia was generally mild and rarely led to stopping. It also says the stopping rates were closely linked to starting BMI and included people who stopped because they felt they had lost too much; among those with a BMI of 35 or above, 8.8% and 12.1% stopped because of side effects against 4.8% on placebo (Lilly, December 2025).
TRANSCEND-T2D-1: a diabetes trial
A fifth phase 3 trial tested retatrutide as a diabetes treatment in 537 adults for 40 weeks. Its published report says the most frequent side effects were generally mild to moderate digestive ones that eased over time, and that 2% to 5% stopped because of side effects against 0% on placebo (Bajaj 2026).
Lilly reported a sixth phase 3 trial, TRANSCEND-T2D-2, on 28 October 2026: at 80 weeks, 4.8% and 7.9% stopped because of adverse events on retatrutide 9 mg and 12 mg, against 2.7% on semaglutide 2 mg (Lilly, October 2026).
Heart events: too few to tell
TRIUMPH-3 recorded major cardiovascular events, but fewer than expected in both groups, which limits what the numbers can show (Lilly, July 2026):
- Heart attack, stroke or cardiovascular death (MACE-3): 27 events on retatrutide against 23 on placebo, a hazard ratio of 1.12, with a 95% confidence interval from 0.64 to 1.96.
- A wider set: death from any cause, heart attack, stroke, a heart failure event or a procedure to reopen a heart artery (MACE-5): 44 against 52, a hazard ratio of 0.82, interval 0.55 to 1.22.
Both intervals run from a lower risk to a higher one. Read honestly, they are compatible with benefit, with no difference and with harm, and they settle nothing either way. The trial built to answer the question, TRIUMPH-Outcomes, aims to enrol about 10,000 people and is expected to complete in 2029 (ClinicalTrials.gov).
What these numbers do and do not cover
They describe retatrutide made by Lilly and given in trials, with doses raised in steps and participants monitored. They say nothing about products sold online under the name. HSA has received reports of anaphylaxis, abdominal pain, diarrhoea and vomiting after people used unapproved injectable peptides bought online (HSA 2026), and the reta peptide page covers that warning. Anaphylaxis, which HSA lists among those reports, usually starts within minutes. The NHS lists signs including a sudden swelling of the lips, mouth, throat or tongue, struggling to breathe, a tight throat or difficulty swallowing, and a rash that is swollen, raised or itchy, and says these can be signs of a serious allergic reaction that may need immediate treatment in hospital (NHS). In a medical emergency in Singapore, call 995 or go to the nearest hospital emergency department (medical disclaimer). HSA also reports hospitalisation from severe vomiting after people took GLP-1 medicines obtained overseas or online without a prescription and medical supervision (HSA 2026). The side effects of the GLP-1 medicines registered in Singapore are covered in the side-effects article, and retatrutide's status here has its own page.
Read the transcript
Retatrutide side effects. Reta side effects. Here's what the phase 3 trials found, in short.
Mostly digestive, plus one odd one: a skin tingle called dysesthesia.
I'm Dr Quek, a Singapore-registered doctor, and the doctor behind the GetLean GLP-1 Taper Plan.
The full papers from two of the big trials came out on the twenty-ninth of September. Let's go through them.
In this video: the gut side effects, the skin tingle, who stopped, the heart question, and what it means for reta sold online.
A quick note up front. Retatrutide and orforglipron are not registered in Singapore, and GetLean does not prescribe or supply them. GetLean does prescribe and supply HSA-registered GLP-1 medications, after a consultation with Dr Quek.
Question one. What are the most common retatrutide side effects?
It's the gut. The biggest trial with results so far followed more than two thousand three hundred adults for eighty weeks.
Nausea was reported by nearly three in ten people on the lowest dose, and more than four in ten on the highest. On placebo, the dummy injection, about one in seven.
Diarrhoea was close behind. About a quarter on the lowest dose, about a third on the two higher doses, and about one in seven on placebo.
Vomiting went from about one in ten on the lowest dose to about one in four on the highest. Placebo was about one in twenty.
Constipation was about one in four on every dose, against about one in ten on placebo.
For nausea and vomiting, the higher the dose, the more people reported it.
Lilly says these are the same kinds of side effects seen in trials of other medicines in the same family.
A few others showed up. Urinary tract infections, seven to nine in a hundred, against about five on placebo. And in another trial, low blood pressure in up to six in a hundred, against fewer than one.
Question two. What is dysesthesia, the skin tingle you keep hearing about? And did side effects make people stop?
It's an unpleasant feeling on the skin, like tingling or burning, with nothing outside causing it.
In the biggest trial, about one in eight on the two higher doses reported it. On placebo, about one in a hundred.
Lilly says it was mostly mild to moderate. Most people carried on, and most cases settled during treatment.
The highest rate was in a smaller trial of four hundred and forty-five adults. About one in five on the highest dose, against less than one in a hundred on placebo. Lilly says those events were generally mild, and rarely made people stop.
If you ever notice a strange tingling or burning on your skin, on any medicine, tell your doctor. It's worth a conversation.
Let's take stopping. In the biggest trial, on the lowest dose, about four in a hundred stopped. On placebo, about five in a hundred.
On the middle dose, about seven in a hundred. On the highest, about eleven in a hundred. That's more than twice the placebo number.
The highest stopping rate was in the smaller trial: about twelve and eighteen in a hundred, against four on placebo.
But Lilly says that was closely linked to the body mass index people had at the beginning, and it included people who stopped because they felt they'd lost too much weight.
So most people did not stop because of side effects. But in the biggest trial, stopping went up with the dose.
Question three, and it's the big one. Is retatrutide safe? Let's begin with the heart.
The honest answer on the heart is, we don't know yet.
One trial followed nearly two thousand adults who already had cardiovascular disease. Major heart events, meaning heart attack, stroke or death from a heart cause, were twenty-seven on retatrutide and twenty-three on placebo.
On a wider count, it was forty-four against fifty-two.
There were too few events to tell. The numbers are compatible with it helping, making no difference, or doing harm.
A trial built to answer this, with about ten thousand people, is expected to finish in twenty twenty-nine.
So is it safe? No regulator has approved it yet. And most of the numbers I've given you are Lilly's own announced results. A regulator would review the full data before approving anything.
Question four, and the one that matters most in Singapore. Is the reta peptide sold online the same as the medicine in these trials?
You can't assume so. Everything I've told you is about Lilly's retatrutide, in a trial, with doses raised in steps and the trial team watching. It says nothing about products sold online under the name.
On the twenty-fifth of September, Singapore's HSA warned that injectable peptides still in clinical trials, retatrutide among them, are being marketed online for weight loss. No regulator, HSA included, has approved it as a medicine.
HSA has had reports of serious allergic reactions, called anaphylaxis, plus stomach pain, diarrhoea and vomiting, after people used unapproved peptides from online sellers.
It says a label like "research use only" is a warning sign. And you can't be sure what's really inside: the right ingredient, the right amount, or something contaminated. That's a different risk from anything in the trial data.
Last question. What if you've used one of these products and something feels wrong?
HSA's advice is to stop using products from unauthorised sellers, and to talk to your doctor first.
Some things can't wait. Swelling of the lips, face or throat, trouble breathing, or a rash that spreads fast. Call nine nine five, or go to an emergency department.
HSA also has reports of people in hospital with severe vomiting after medicines obtained overseas or online without a prescription.
So if the vomiting is severe, or you can't keep fluids down, see a doctor straight away. Don't sit it out.
And tell the doctor exactly what you used. They can't help if they don't know.
If you're considering GLP-1 medication to reach your weight goal, and you'd like to taper off it one day, I invite you to visit getleanclinic.sg to learn about our approach and the GetLean GLP-1 Taper Plan.
Read the transcript
What are the side effects of retatrutide, or Reta?
Mostly digestive: nausea, diarrhoea, vomiting and constipation. Plus one unusual one, a skin tingle called dysesthesia.
I'm Dr Quek, a Singapore-registered doctor, and the doctor behind the GetLean GLP-1 Taper Plan.
Retatrutide and orforglipron are not registered in Singapore, and GetLean does not prescribe or supply them.
How common are the gut side effects?
In the biggest trial with results so far, more than two thousand three hundred adults over eighty weeks, nausea hit more than four in ten people on the highest dose. On placebo, about one in seven.
Diarrhoea, vomiting and constipation were all more common than on placebo too. And for nausea and vomiting, the higher the dose, the more people had it.
What is dysesthesia?
An unpleasant feeling on the skin, like tingling or burning, with no obvious outside cause.
About one in eight on the two higher doses reported it, against about one in a hundred on placebo. Lilly says it was mostly mild to moderate, and most cases settled during treatment.
Did side effects make people stop?
Most didn't. On the highest dose, about eleven in a hundred stopped, more than twice the placebo number.
Is retatrutide safe for the heart?
The honest answer is, we don't know yet. In a trial of nearly two thousand adults with heart disease, there were too few heart events to tell either way.
A trial built to answer this, with about ten thousand people, is expected to finish in twenty twenty-nine.
Is the Reta sold online the same as the trial medicine?
You can't assume so. Everything I've told you is about Lilly's retatrutide, given in trials. It says nothing about products sold online under the name.
HSA has warned about unapproved peptides, and has had reports of serious allergic reactions after people used peptides from online sellers.
If you've used one and something feels wrong, stop, and tell a doctor exactly what you used. If your lips, mouth or throat swell, or you're struggling to breathe, call nine nine five.
If you're considering GLP-1 medication to reach your weight goal, and you'd like to taper off it one day, I invite you to visit getleanclinic.sg to learn about our approach and the GetLean GLP-1 Taper Plan.
Common questions
What are the most common side effects of retatrutide?
Digestive ones. In TRIUMPH-1, nausea was reported by 28.6% to 42.4% across the three doses against 14.8% on placebo, and diarrhoea by 25.2% to 34.1% against 13.5% (Lilly, May 2026). Constipation and vomiting were also more common than on placebo.
What is dysesthesia on retatrutide?
An abnormal, unpleasant skin sensation. In TRIUMPH-1 it was reported by 5.1%, 12.3% and 12.5% on 4 mg, 9 mg and 12 mg against 0.9% on placebo; Lilly says the events were generally mild to moderate, most resolved during treatment, and most participants continued (Lilly, May 2026). The highest rate so far was in TRIUMPH-4, at 20.9% on 12 mg against 0.7%, where Lilly says it rarely led to stopping (Lilly, December 2025).
How many people stopped retatrutide because of side effects?
It varied by trial and dose. In TRIUMPH-1, 4.1%, 6.9% and 11.3% on 4 mg, 9 mg and 12 mg, against 4.9% on placebo (Lilly, May 2026). The highest was TRIUMPH-4, at 12.2% and 18.2% on 9 mg and 12 mg against 4.0%, which Lilly says was closely linked to starting BMI and included people stopping because they felt they had lost too much (Lilly, December 2025).
Does retatrutide affect the heart?
The evidence so far cannot say. In TRIUMPH-3 there were 27 major cardiovascular events on retatrutide and 23 on placebo, a hazard ratio of 1.12 with a confidence interval from 0.64 to 1.96 (Lilly, July 2026), which is compatible with benefit, no difference or harm. A dedicated outcomes trial of about 10,000 people is expected to complete in 2029 (ClinicalTrials.gov).
Is retatrutide safe?
No regulator has yet evaluated it: HSA states that none, including HSA, has approved it as a medicine (HSA 2026). The figures on this page are company-announced trial results, which a regulator would review in full before any approval.