Your stomach usually tells you first.
If you have started retatrutide, or you are about to, you probably want three answers: which retatrutide side effects are normal, which are not, and how long they last. That is the right order. This page puts the published trial numbers from six studies with more than 6,700 people next to what 220 people taking it have posted online, and shows where the two disagree.
Short answer: the most common retatrutide side effects (also searched as reta or reta peptide side effects) are nausea (42.4%), diarrhea (32.0%), constipation (26.1%) and vomiting (25.3%) at 12 mg in TRIUMPH-1, against 14.8%, 13.5%, 10.9% and 4.8% on placebo, plus skin tingling (dysesthesia) in 12.5% against 0.9% (Lilly, May 21, 2026). Most were mild to moderate and eased with time.
🔑 Key Takeaways
- Most side effects are stomach-related, show up early and fade. A few do not.
- The starting dose changed nausea more than the final dose did.
- The skin side effect is real, dose-linked, and no longer unique to retatrutide.
- Online, people complain about different things than trial tables count. Fatigue and sleep lead.
- For anyone using an unapproved vial, what is in the vial may matter more than the drug.
Data checked October 24, 2026. Trial figures come from the published papers, Lilly's medical-information pages and registered trial records. User reports were read on Reddit and X between November 2025 and October 2026. Every source is listed at the end.
Retatrutide side effects at a glance
Start with the biggest trial.
TRIUMPH-1 followed 2,339 adults with obesity for 80 weeks. Everyone started at 2 mg a week and stepped up every 4 weeks to a target of 4, 9 or 12 mg. The table puts its 12 mg results next to placebo and next to how often each symptom came up in the 220 user posts we read.
Two things stand out. Placebo groups had these symptoms too (14.8% had nausea without the drug), so part of what you feel would happen anyway. And the user column tilts toward fatigue, heart rate, sleep and mood, which the trial tables either rank lower or do not report at all. More on why further down.
The most common side effects, dose by dose
Higher dose, more side effects. Mostly.
Nausea, diarrhea, constipation and vomiting were the big four at every dose. Nausea rose from 28.6% at 4 mg to 42.4% at 12 mg, and vomiting more than doubled between 4 mg and 9 mg. Diarrhea was slightly higher at 9 mg than at 12 mg, which is a reminder that these are separate groups of people, not one person climbing the ladder.
The same pattern held in every trial, with different sizes:
*TRIUMPH-2 counts stopping for side effects or death. TRIUMPH-3 and TRIUMPH-4 tested only 9 and 12 mg.
A number you will see quoted wrongly. Many pages say retatrutide causes nausea in "60% of people at 12 mg". In the phase 2 trial, 60% was the rate in the group that jumped straight to 4 mg on its way to 8 mg. The 12 mg group, which started at 2 mg, had 45% (Jastreboff et al., NEJM 2023).
Why the starting dose matters more than the final dose
This is the most useful chart on the page.
In the phase 2 trial, two groups ended on the same 8 mg dose. The group that started at 2 mg had nausea 17% of the time. The group that started at 4 mg had it 60% of the time, and vomiting jumped from 6% to 26%. That is why TRIUMPH-1 started everyone at 2 mg and allowed up to two permanent dose reductions for stomach side effects in the first 20 weeks.
If the numbers on your vial and your plan are getting tangled, our explainer on which retatrutide numbers are doses and which are vial sizes sorts them out. Six of the user posts we read described an accidental overdose.
Retatrutide skin side effects: dysesthesia explained
It feels like a sunburn you never got.
Dysesthesia means the skin feels wrong: burning, tingling, painful to touch, or sensitive to clothing. Lilly's summary of the four TRIUMPH trials calls the events "generally mild to moderate". In the phase 2 trial, none were severe and none made anyone stop.
The rate swings a lot between trials, from 4.4% in people with type 2 diabetes to 20.9% in TRIUMPH-4, where most participants had a BMI of 35 or more. So "1 in 5" is true for one trial, not for retatrutide in general. Across the other trials at 12 mg, it was closer to 1 in 8 or lower.
It is not unique to retatrutide anymore. The 2026 Wegovy label reports dysesthesia in 22% of people on the new 7.2 mg dose and 6% on 2.4 mg, against 0.3% on placebo. Among people on 7.2 mg who had it, 18% had not recovered by the end of the trial, and 45% of those re-escalated after it cleared had it come back (FDA safety labeling change, Wegovy). No retatrutide trial has published how long the symptom lasts.
Users describe both ends of that range:
“some mild nausea and skin tingling the first week or two, but mostly went away.”
““Sunburn” side effect lasted a couple of months.”
“I unknowingly pinned 8 mg. Experienced full body dysesthesia for three weeks (barely slept at night), severe nausea”
After an accidental overdose: X post
Heart rate and blood pressure
Your watch may notice before you do.
In the phase 2 trial, 24-hour monitoring showed heart rate up by an average of 9.2 beats per minute at 12 mg by week 24, easing to 6.7 by week 36 and 6.0 at rest by week 48. Placebo moved by less than 1. Cardiac arrhythmias were reported in 11% of the 12 mg group against 3% on placebo, and one serious heart-rhythm event (QT prolongation) happened in a person also taking the anti-nausea drug ondansetron (NEJM 2023 and appendix). The phase 3 heart-rate numbers sit in the full papers and have not been published elsewhere.
Blood pressure goes the other way. In TRIUMPH-1, low blood pressure was reported in 8.8% at 12 mg against 0.9% on placebo, rising to 11.3% in people already on blood-pressure medicine. In TRIUMPH-3, which enrolled people with established heart disease, major heart events were 27 on retatrutide against 23 on placebo for the narrow measure (hazard ratio 1.12) and 44 against 52 for the broad one (hazard ratio 0.82). That trial was not built to settle heart safety; a dedicated outcomes trial is still running.
Online, a faster heart rate was the third most common complaint:
“after my second week at 2mg, I injected and my heart rate suddenly went through the roof almost instantly.”
“58 to 90+ on 8mg Reta. Had to stop and switched to Tirz and rhr is slowly coming back down to normal levels”
How many people stop retatrutide because of side effects
Most people stayed on it.
At 12 mg, between 5.1% and 18.2% stopped because of side effects, against 0% to 5% on placebo. At 4 mg in TRIUMPH-1 the rate was 4.1%, slightly below placebo. The highest figure, 18.2% in TRIUMPH-4, includes people who stopped for what Lilly called "perceived excessive weight loss"; among participants who started with a BMI of 35 or more it was 12.1%.
Serious side effects: what the trials found
Rare, but worth knowing by name.
- Serious adverse events. 10.5% at 12 mg against 5.5% on placebo in TRIUMPH-1.
- Pancreatitis. Confirmed cases in TRIUMPH-1 were 1, 3 and 4 at 4, 9 and 12 mg, against 2 on placebo. The phase 2 trial had one case, in the 12 mg group on day 14.
- Gallbladder. Three biliary events in the phase 2 trial; gallbladder problems are a known risk across this drug class, especially with fast weight loss.
- Low blood sugar. In TRIUMPH-2 (type 2 diabetes), level 2 or 3 low blood sugar was 3% at 12 mg against 2% on placebo. TRANSCEND-T2D-1 had no severe episodes.
- Urinary tract infections. 8–9% across doses in TRIUMPH-1 against 5% on placebo; 92% were in women, mostly mild to moderate, and none led to stopping.
- Eyes. Diabetic eye complications in TRIUMPH-2 were 5%, 5% and 4% on retatrutide against 9% on placebo.
- Kidneys. A follow-up analysis of the phase 2 trial found kidney filtration (eGFR) improved by 8.5 mL/min/1.73m² at 12 mg compared with placebo at week 48.
- Deaths. TRIUMPH-1 recorded 0, 3 and 1 deaths at 4, 9 and 12 mg and 2 on placebo; in TRIUMPH-2 all deaths were judged unrelated by investigators. Neither trial was designed to judge rare causes.
Hair loss has no published rate for retatrutide yet. It appears in the Zepbound label at 5% on 15 mg, and only one of the 220 user posts we read mentioned it. Lean-muscle loss figures from the body-composition substudy have not been published in a form we could check. For the wider question of whether the risks are worth it, see is retatrutide safe.
What real users report about retatrutide side effects
Trials count. People describe.
We read first-person posts from people taking retatrutide on Reddit (160 posts from r/Retatrutide, r/RetatrutideWomen, r/Peptides and r/Biohackers) and X (60 posts), dated November 2025 to October 2026, one report per person. We coded each post for the symptoms it mentioned. Public Facebook groups could not be read without logging in, so none are included. Almost everyone was using unapproved vials, the median dose was 2 mg a week, and the median time on it was 5 weeks.
The right-hand chart is a much bigger analysis of the same communities, published in JAMA Network Open on October 14, 2026: 13,589 Reddit users reported taking retatrutide, and 7,823 described at least one symptom beyond weight and appetite loss. Both lists put fatigue near the top, and both show heart-rate and sleep complaints that trials rank lower. One reason is who posts: people with a problem write more than people without one. Another is the product. Nobody online knows exactly what dose their vial delivers.
Stomach and appetite
“I did experience some mild nausea during that first week, particularly when I ate a larger meal than I probably needed.”
“I was puking like every half hour and couldn’t even keep down water so I got dangerously dehydrated.”
Hospitalized for 6 days (the poster also had other conditions): Reddit, r/Retatrutide, after moving from 2 to 4 mg
Energy, sleep and mood
“In the beginning, I did struggle a bit with low energy, poorer sleep, and a higher heart rate, but over time those side effects settled”
“No issues at 1mg for 6 weeks and then one day quit sleeping.”
“The past 6 days has been absolute hell. I have been full of anxiety and it is making me feel insane.”
“Sex drive is way down but I can still get into sex several times a week (and enjoy it), but it takes more effort.”
No side effects
Seven percent of the posts we read said they had none.
“I have been on reta for about 4 months and have had no side effects.”
“For me: no discernible impact. Went up to 5.25mg per week.”
What users say helped
These are tips people shared, not medical advice: fluids and electrolytes for fatigue, headache and dizziness; staying longer on a lower dose or stepping back to the last dose that felt fine; smaller meals, protein first, and skipping alcohol and fried food around injection day; injecting in the morning when sleep suffers. Some mention keeping an anti-nausea drug on hand. Given the heart-rhythm event in the phase 2 trial that involved ondansetron, ask a doctor before combining the two.
The bigger risk: what is actually in the vial
Retatrutide is not approved anywhere yet.
Lilly plans to file with the FDA in the first quarter of 2027. Until then, every vial sold online is unapproved, and FDA states that retatrutide "cannot be used in compounding under federal law" (FDA). The trial safety numbers above describe pharmaceutical-grade drug at known doses. A gray-market vial can differ on both counts.
- Deaths reported to FDA. CBS News reported on October 13, 2026 that FDA received reports of two deaths after people took bootleg retatrutide: a 41-year-old woman with cardiac arrest and a 49-year-old with severe dehydration, malnutrition and cardiac arrest. The reports were not verified and do not prove the drug caused them.
- Liver injury in Australia. Victoria's health department linked six cases of acute liver injury since January 2026 to products labelled retatrutide, and suspects a contaminant.
- UK reports. The BMJ reported 77 Yellow Card reports to the UK regulator, 59 of them serious and one fatal.
- Vials that are not what they say. A lab test commissioned by CBS News found one vial labelled retatrutide contained no peptide at all, plus bacterial colonies.
- Poison-center calls. CBS reported retatrutide exposures rising from 249 to 460 to 862 a quarter during 2026.
If you are comparing retatrutide for sale anyway, a third-party certificate of analysis that matches your batch number is the minimum check, and even that cannot tell you about sterility or endotoxins unless they were tested. PeptideDeck earns a commission from some vendors we link to; it does not change any number on this page. Our guides on mixing retatrutide and injecting it cover the handling steps that cause their own problems when done wrong.
Retatrutide vs semaglutide vs tirzepatide: side effects compared
Similar stomach, different skin.
Retatrutide 12 mg from TRIUMPH-1 (80 weeks); Wegovy 2.4 mg and Zepbound 15 mg from their US labels (68 and 72-week trials). Different trials and populations, so read this as a rough guide, not a ranking. The stomach side effects of retatrutide 12 mg look a lot like Wegovy 2.4 mg and run higher than Zepbound 15 mg. The skin effect sits between the two Wegovy doses. For a head-to-head on results as well as side effects, see retatrutide vs tirzepatide.
When to stop and get help
Some symptoms should not be waited out.
- Severe stomach pain that spreads to your back, with or without vomiting (possible pancreatitis).
- Pain in the upper right abdomen, fever or yellowing skin or eyes (gallbladder or liver).
- Vomiting or diarrhea that stops you keeping fluids down for more than a day, or very little urine (dehydration and kidney strain).
- A racing or irregular heartbeat at rest, chest pain, fainting or shortness of breath.
- Shakiness, sweating and confusion, especially if you also take insulin or a sulfonylurea (low blood sugar).
- Thoughts of self-harm or a sharp change in mood.
Tell the clinician exactly what you took, at what dose and from where. If you are on prescribed medication for blood pressure, diabetes or your heart, do not stop or change it without your doctor.
Frequently Asked Questions
Sources
- Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med 2023;389:514-526 (PMID 37366315), plus supplementary appendix. Funded by Eli Lilly.
- Jastreboff AM et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). N Engl J Med, Sept 29, 2026 (PMID 42814954).
- Lilly Medical Information: TRIUMPH-1 results and adverse-event table.
- Bellido V et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). Lancet 2026 (PMID 42810372).
- Lilly Medical Information: TRIUMPH-3 results; cardiovascular events.
- Eli Lilly press release: TRIUMPH-4 topline results, Dec 11, 2025.
- Bajaj HS et al. TRANSCEND-T2D-1. Lancet 2026 (PMID 42250575); Lilly ADA 2026 poster.
- Lilly Medical Information: dysesthesia in the TRIUMPH trials.
- Lilly Medical Information: urinary tract infections in the TRIUMPH trials.
- Heerspink HJL et al. Retatrutide and kidney function, phase 2 post hoc analysis. Kidney Int Rep 2025.
- Sehgal NKR et al. Self-reported adverse effects among social media users taking nonapproved retatrutide. JAMA Netw Open, Oct 14, 2026.
- FDA safety labeling change: Wegovy (dysesthesia at 2.4 mg and 7.2 mg).
- Wegovy US prescribing information (adverse reactions).
- Zepbound US prescribing information, Table 1.
- FDA: concerns with unapproved GLP-1 drugs used for weight loss.
- CBS News: deaths reported to FDA after bootleg retatrutide, Oct 13, 2026.
- CBS News: lab tests of retatrutide vials, Oct 21, 2026.
- Victoria Department of Health: toxicity linked to unapproved peptide retatrutide.
- The BMJ: UK Yellow Card reports for retatrutide, 2026.
- User reports: 160 Reddit and 60 X posts, read October 24, 2026; each quote above links to its post.
Medical disclaimer: This article summarises published trial data and public user reports. It is not medical advice. Retatrutide is not approved by the FDA or any other regulator, and products sold online are unapproved and unregulated. Talk to a licensed clinician before starting, stopping or changing any medication.
