Retatrutide side effects by dose: TRIUMPH-2 Lancet data

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In TRIUMPH-2, published in The Lancet on 29 September 2026, the most common retatrutide side effects were gastrointestinal. On 12 mg, 28% of participants had nausea and 34% had diarrhea, against 8% and 13% on placebo. Two newer signals rose with dose: dysesthesia, an abnormal skin sensation (7% vs 1%), and hypotension (6% vs under 1%). Stopping treatment for side effects or death was 4%, 12% and 8% on 4, 9 and 12 mg, against 5% on placebo. Reddit users in October 2026 also describe low libido, poor sleep and a faster resting heart rate. The trials document a heart-rate rise that peaks and then falls; the papers we read report nothing on libido or sleep. Retatrutide is investigational. These are trial results, not a guide to research-peptide use.

Editorial illustration - molecular structure, stethoscope, vials, dropper, plant, ECG trace, and clinical-paper scraps on dark red collage background. — editorial illustration · Editorial illustration. Clinical-trial readouts compose stethoscope, ECG, vial, and the molecule itself into one weighted signal.

What side effects did TRIUMPH-2 report at each dose?

TRIUMPH-2 enrolled 1,152 adults with obesity and type 2 diabetes and ran 80 weeks. The Lancet paper (29 September 2026, doi 10.1016/S0140-6736(26)01861-1) reports these rates in the safety population, meaning everyone who received at least one dose:

Event	4 mg	9 mg	12 mg	Placebo
Diarrhea	27%	34%	34%	13%
Nausea	14%	21%	28%	8%
Vomiting (Lilly)	5.5%	10.2%	15.7%	4.2%
Constipation (Lilly)	14.0%	16.2%	16.8%	9.4%
Decreased appetite (Lilly)	5.8%	12.3%	17.1%	4.5%
Dysesthesia	4%	6%	7%	1%
Hypotension	1%	5%	6%	under 1%
Stopped treatment for side effects or death	4%	12%	8%	5%
Deaths	2	3	1	1

Rows marked "Lilly" come from Lilly's TRIUMPH-2 release of the same day, which gives one decimal place. The Lancet abstract does not list those three events. Investigators judged all seven deaths unrelated to the study drug.

Two things in this table are easy to miss.

Dropout did not rise in step with dose. The 9 mg arm lost 12% of its participants to side effects or death, more than the 12 mg arm at 8%. Lilly's release gives the same pattern with decimals: 3.8%, 11.6% and 7.7% against 4.9% on placebo. The paper's abstract does not explain it. With roughly 285 people per arm, a difference of about ten participants can produce a gap that size.

The GI rates in people with diabetes run lower than in TRIUMPH-1. In TRIUMPH-1, which enrolled people without diabetes, nausea on 12 mg reached 42.4% (Lilly topline, May 2026). TRIUMPH-2 reports 28%. Both trials used the same doses and the same 80 weeks, so the population is the likeliest difference. We cover the two trials side by side in retatrutide Phase 3 results.

What we read

The TRIUMPH-2 Lancet abstract (29 September 2026); Lilly's TRIUMPH-2 release of the same date; the TRIUMPH-1 abstract in NEJM (29 September 2026) and the safety section of the full paper; Lilly's earlier topline releases for TRIUMPH-1, -3 and -4; the Phase 2 publication (Jastreboff et al., NEJM 2023); and the Phase 1b study (Urva et al., The Lancet 2022). We also read the Reddit threads linked in this article, between August and October 2026. We did not read the TRIUMPH-2 supplementary appendix, so rarer events that appear only in its tables are not on this page.

What is dysesthesia on retatrutide?

Dysesthesia is an abnormal, unpleasant skin sensation: burning, tingling, or pain from a light touch that should not hurt. In TRIUMPH-2 it affected 4%, 6% and 7% of participants on 4, 9 and 12 mg, against 1% on placebo.

The full TRIUMPH-1 paper names dysesthesia, injection-site reactions and hypotension as the most frequent "adverse events of special interest" that were more common with retatrutide. It describes those events as mostly mild or moderate and judged nonserious by investigators. Neither paper's abstract proposes a mechanism, and we will not guess at one.

This is the side effect Reddit users describe as skin sensitivity. A thread titled "skin problems on reta?" collects reports of skin that hurts to touch. The trial signal is real; the Reddit reports come from unverified product, so the two cannot be matched one-to-one.

Why does retatrutide cause low blood pressure?

TRIUMPH-2 reported hypotension in 1%, 5% and 6% of the three dose arms, against under 1% on placebo. The full TRIUMPH-1 paper adds the context that matters most: reported hypotension was more common in participants who were already taking blood-pressure medication.

Weight loss itself lowers blood pressure, so a person whose antihypertensive dose was set at a higher body weight can end up over-treated. That is a reason the trials ran under medical supervision. Anyone using retatrutide outside a trial has no one adjusting the other drugs.

Does retatrutide raise resting heart rate?

Yes, and the published data describes a rise that peaks and then falls. The full TRIUMPH-1 paper reports that mean pulse rate increased with retatrutide, peaked at week 20 in the 9 mg and 12 mg groups, and decreased after that. The per-dose values sit in the paper's supplementary table, which we have not read.

The only per-dose numbers we have found come from the small Phase 1b study (Urva et al., The Lancet 2022, 12 weeks, people with type 2 diabetes). In its three highest-dose groups, pulse rate rose by 2 to 13 bpm measured 24 hours after the last dose, and by −1 to 10 bpm averaged over the final four weeks.

An earlier version of this page gave a "1–3 bpm" figure. We could not trace it to a primary source and have removed it.

On Reddit the thread "RHR on Reta" describes a resting heart-rate rise of about 14 bpm over eight weeks. That is one person's reading, on product of unknown dose and identity, and it sits at the top of the Phase 1b range. It is also the kind of change worth taking to a doctor rather than to a forum.

What remains open. No cardiovascular outcomes result exists. TRIUMPH-3 enrolled 1,949 people with established cardiovascular disease and met its weight endpoint in July 2026, but a weight endpoint is not a test of heart attacks, strokes or cardiovascular deaths.

Retatrutide side effects vs tirzepatide

The fair comparison for TRIUMPH-2 is SURMOUNT-2, tirzepatide's trial in the same population (obesity plus type 2 diabetes, The Lancet 2023). No head-to-head trial exists, so this is a cross-trial read.

	Tirzepatide (SURMOUNT-2, 72 weeks)	Retatrutide (TRIUMPH-2, 80 weeks)
Weight change, top dose, treatment-regimen estimand	−14.7% (15 mg) vs −3.2%	−18.8% (12 mg) vs −5.1%
Stopped for side effects	under 5% across tirzepatide arms	4% / 12% / 8% for side effects or death (4 / 9 / 12 mg) vs 5% placebo
Most frequent events	nausea, diarrhea, vomiting	diarrhea, nausea, then vomiting and constipation
Flagged beyond GI	none in the abstract	dysesthesia, hypotension

The Lancet paper reports −18.8% on 12 mg at week 80 under the treatment-regimen estimand, which counts every randomised participant whether or not they stayed on the drug. Lilly's headline 20.8% uses the efficacy estimand, which estimates the effect had everyone stayed on treatment.

The pattern is consistent with the extra glucagon-receptor action: more weight lost, a higher dropout rate at 9 and 12 mg, and two signals the tirzepatide abstract does not mention. For the full efficacy comparison, see retatrutide vs tirzepatide.

When do GI side effects happen on retatrutide?

During escalation. TRIUMPH-2 started everyone on 2 mg and stepped the dose up every four weeks, so the 12 mg arm took 16 weeks to reach its target. The week-by-week ladder is in retatrutide dosing protocols.

The 2024 multi-society GLP-1 guidance from the American Society of Anesthesiologists and four other societies makes the same point for approved GLP-1 drugs: stomach emptying is slowest early in treatment and while the dose is rising. That guidance does not cover retatrutide by name, but the mechanism is shared.

What about injection-site reactions?

The full TRIUMPH-1 paper lists injection-site reactions among the most common adverse events of special interest that were more frequent with retatrutide, mostly mild or moderate. The TRIUMPH-2 abstract does not report a rate.

What users are reporting on Reddit (October 2026)

Two of the four symptoms Reddit users raised in early October match trial data: a faster resting heart rate and skin pain. Low libido and poor sleep do not appear in the papers and releases we read. Between 3 and 8 October 2026, four threads drew 79 to 142 comments each (counts as of 10 October).

Symptom	Trial data	Community reports (October 2026)	Notes
Faster resting heart rate	Documented. Phase 2 (NEJM 2023): dose-dependent rise, peak at 24 weeks, then decline. TRIUMPH-1 (NEJM 2026): peak at week 20 on 9 and 12 mg, then decline. Phase 1b: 2 to 13 bpm.	83 to 101 bpm at rest on 2 mg after five weeks (one poster); others in the thread report smaller rises	An 18 bpm rise is above the Phase 1b range. The Phase 2 authors note that glucagon and GLP-1 can raise heart rate.
Low libido	Not reported in the papers and releases we read. We have not read the supplementary tables.	Two threads, 134 and 126 comments	One poster asks whether low intake or fast weight loss is the cause. No trial data separates these.
Poor sleep	Not reported in the papers and releases we read. We have not read the supplementary tables.	One thread, 79 comments; the poster says it resolved off the drug and returned on restart	A stop-restart pattern in one person is a reason to look for a signal, not evidence of one.
Skin pain or sensitivity	Documented. Dysesthesia in 4%, 6% and 7% on 4, 9 and 12 mg vs 1% on placebo (TRIUMPH-2). Phase 2: skin sensitivity in 7% vs 1%.	One thread, 19 comments	The best match between Reddit and the trials. See the dysesthesia section above.

"Not reported" means absent from the abstracts, main texts and releases we read. A rarer event could still sit in the supplementary appendices.

What did the posters say?

This is anecdote, kept apart from the trial data. None of these posters used trial product, their vials have unknown identity and dose, and no clinician checked their symptoms. A fifth thread, on "not working", drew 476 comments and is covered in retatrutide not working.

Libido. A poster ten weeks in wrote that "my libido has absolutely tanked" and also described low calorie intake (r/Biohacking, 134 comments). A second poster: "My libido has become extremely low since using retatrutide. I've stopped taking it, but I haven't noticed any improvement yet" (r/Biohacking, 126 comments).
Resting heart rate. "My heart rate has increased significantly, from my usual 83 BPM to 101 BPM while at rest," five weeks in (r/Biohacking, 142 comments).
Sleep. "I wake up several times per night and feel like i cant get any REM sleep at all." The poster says it went away on stopping and came back on restarting (r/Retatrutide, 79 comments).
Skin pain. A smaller thread: "the hair on my legs hurt," with pain "like I had a very bad sunburn with no rash" (r/BodyHackGuide, 19 comments). The same poster was also taking other peptides and says the pain stopped about a week after dropping retatrutide.

Two things can cause a Reddit side effect the trial drug would not: a vial holding a different dose or a different compound, and eating far below maintenance, which can lower libido and disturb sleep with no drug involved. If a sustained heart-rate rise or another symptom persists, see a clinician.

What the published data does not cover

Anything past 104 weeks. The longest data is the TRIUMPH-1 extension. Whether dysesthesia or the heart-rate rise persist or fade over years is unknown.

Cardiovascular outcomes. Covered above. This is the main open safety question.

Muscle and lean mass. The trial releases report total weight. Our muscle loss on GLP-1s piece covers what is known for the drug class.

Special populations. Pregnancy, children and hepatic impairment are outside the published TRIUMPH program.

What this does not tell you about research-peptide retatrutide

The trial rates describe pharmaceutical-grade retatrutide titrated under supervision. A research-peptide vial adds two unknowns before any side effect can be attributed: whether the vial holds retatrutide at all, and how much. Our Janoshik 7,164-tests purity analysis documents cross-vendor variance for retatrutide. If side effects are absent, or weight is not moving, the product is the first variable to check. We cover that question in retatrutide not working. Harm reports from outside trials, including two FDA death reports and the rising poison center count, are covered in retatrutide death reports.

Sources

Frequently asked

What are the most common side effects of retatrutide?

Gastrointestinal events. In TRIUMPH-2 (The Lancet, 29 September 2026) diarrhea affected 27%, 34% and 34% of participants on 4, 9 and 12 mg, and nausea 14%, 21% and 28%, against 13% and 8% on placebo. Lilly's release adds vomiting at 5.5% to 15.7% and constipation at 14.0% to 16.8% across the same arms.

Does retatrutide raise your heart rate?

Yes, temporarily in the trial data. The full TRIUMPH-1 paper in NEJM (29 September 2026) reports that mean pulse rate rose with retatrutide, peaked at week 20 on 9 and 12 mg, and fell after that. Reddit users describe larger personal rises, but those readings come from unverified product and no trial supervision.

Is it safe to have anesthesia for surgery while on retatrutide?

No retatrutide-specific guidance exists. For approved GLP-1 drugs, a 2024 multi-society guidance led by anesthesiologists says delayed stomach emptying raises aspiration risk, and flags the dose-escalation phase and active GI symptoms as the highest-risk periods. Tell the anesthesia team what you take and when you last took it.

Why does my body ache on retatrutide?

The trial reports do not answer this. Body or joint aches are not among the adverse events listed in the TRIUMPH-2 Lancet abstract or Lilly's TRIUMPH-2 release. Reddit threads such as "Body aches on Reta" describe the complaint, but with unverified product and no clinical work-up, nobody can attribute it to the molecule.

Can retatrutide cause loss of motivation or low mood?

Not as a reported trial signal. The published TRIUMPH-2 abstract and Lilly release list no psychiatric or mood events among the common adverse events. A Reddit thread titled "loss of ambition on reta" collects user reports of low energy and low drive. Treat those as anecdote and raise persistent mood changes with a doctor.

Does retatrutide cause hair loss?

We have not found a per-arm hair-loss figure in the published retatrutide data. The TRIUMPH-2 Lancet abstract and Lilly's release do not list it among common events. Hair shedding is reported with rapid weight loss in general, so it may appear in the full supplementary tables. We will add a number when we find one.

How long do retatrutide GI side effects last?

The trials report GI events concentrating in the dose-escalation weeks. TRIUMPH-2 stepped every four weeks from 2 mg, so the 12 mg arm escalated for 16 weeks. Reddit posts titled "Still not adjusting" describe users who stay nauseated past that window. The trial data does not separate those people out.

Does retatrutide lower libido?

The trials don't say. Libido and sexual function do not appear in the TRIUMPH-1 and TRIUMPH-2 papers, the Phase 2 paper or Lilly's releases we read; we have not read the supplementary tables. Two October 2026 Reddit threads, with 134 and 126 comments, describe a sharp drop. One poster asks whether low calorie intake is the cause.

Can retatrutide cause insomnia or bad sleep?

No sleep signal appears in the published retatrutide data we read, and we have not seen the supplementary appendices. A 79-comment r/Retatrutide thread from 3 October 2026 describes waking several times a night, with the poster saying it stopped off the drug and returned on restarting. That is one person's report on unverified product.

Why is my heart rate higher on retatrutide?

A heart-rate rise is a documented trial effect. In the Phase 2 NEJM paper it rose with dose, peaked at 24 weeks and then declined; TRIUMPH-1 reports a peak at week 20 on 9 and 12 mg. One Reddit report of 83 to 101 bpm on 2 mg is above the Phase 1b range of 2 to 13 bpm.