Strong human trialsIn clinical trials

Retatrutide side effects

Also known as: LY3437943 · Reta · GLP-3 · GLP-3 RT

Updated Oct 23, 202674 sources

19 side effects reported for Retatrutide: 10 from studies and labels, 9 from users and guides. 10 come with the ways people manage them.

Retatrutide overview

Side effects reported in studies and labels

Rates as each trial or label states them. A rate from one trial does not carry over to research-grade vials or other doses.

From trials and regulators10

Clinical studies and regulatory documents.

Nausea
TRIUMPH-1: about 29% at 4 mg, 38.4% at 9 mg and 42.4% at 12 mg, vs 14.8% on placebo
How people manage it
- Start low. In phase 2, a 2 mg start caused fewer stomach side effects than a 4 mg start.
Diarrhea
TRIUMPH-1: 25.2% at 4 mg, 34.1% at 9 mg, 32.0% at 12 mg, vs 13.5% on placebo. TRIUMPH-3: 30.1% at 9 mg
Constipation
TRIUMPH-1: 23.8% at 4 mg, 25.9% at 9 mg, 26.1% at 12 mg, vs 10.9% on placebo
Vomiting
TRIUMPH-1: 10.6% at 4 mg, 22.8% at 9 mg, 25.3% at 12 mg, vs 4.8% on placebo
How people manage it
- Trials allowed dose cuts when stomach effects were hard to tolerate. Dropping back a step is a normal move.
Dysesthesia (skin tingling, burning or sensitivity)
TRIUMPH-1: 5.1% at 4 mg, 12.3% at 9 mg, 12.5% at 12 mg, vs 0.9% on placebo. TRIUMPH-4: 8.8% at 9 mg, 20.9% at 12 mg. Mostly mild
How people manage it
- Mostly mild in trials. A lower dose is the usual lever if it bothers you.
Stopping because of side effects
TRIUMPH-1: 4.1% at 4 mg, 6.5% at 9 mg, 11.2% at 12 mg, vs 4.6% on placebo. TRIUMPH-4: 12.2% at 9 mg, 18.2% at 12 mg, vs 4%
How people manage it
- Slower steps and holding a dose that works are the main tools people use to stay on.
Higher heart rate
Phase 2: heart rate rose with dose, peaked at 24 weeks, then came down
Low blood pressure symptoms
Dose-dependent in phase 3, and more common in people on blood pressure drugs
Liver enzyme rise
ALT above 3 times normal in 1% of phase 2 participants
Acute pancreatitis
One case in the phase 2 trial

Side effects users and guides report

What people post and what dosing guides list. These are reports, not measured rates.

From users and guides9

Community reports, competitor and vendor guides, media.

Nausea: guide tips for getting through it
No separate rate. These are a guide's tips for the trial nausea above
How people manage it
- Hold the current dose 2 to 4 extra weeks before stepping up if nausea is rough.
- Eat smaller meals and lead with protein.
Diarrhea: guide tips for getting through it
No separate rate. These are a guide's tips for the trial diarrhea above
How people manage it
- Drink 2 to 3 liters of fluid a day and add electrolytes.
- Hold the dose longer before the next step up.
Constipation: guide tips for getting through it
No separate rate. These are a guide's tips for the trial constipation above
How people manage it
- Keep fluids up.
- Step up slowly and hold a dose longer if needed.
Vomiting: guide tips for getting through it
No separate rate. These are a guide's tips for the trial vomiting above
How people manage it
- Smaller, protein-first meals.
Skin tingling, pins and needles, sunburn-like skin
A recurring r/Retatrutide topic, reported at doses as low as 1 to 2.5 mg, often 2 to 3 days after a shot or during cardio
How people manage it
- Some posters add vitamin B6 or B12. That is a community habit, not something tested.
Raised resting heart rate and palpitations
Commonly reported on r/Retatrutide and a frequent reason posters taper or move back to tirzepatide. An observational grey-market study also linked unapproved use to more cardiovascular symptoms
How people manage it
- Posters who are bothered by it taper the dose or switch back to tirzepatide.
Early appetite loss, nausea after small meals, light-headedness
Described in a community diary. The strong appetite loss eased over time; spicy food was harder to tolerate
Fatigue and headache
Reported without rates
Anxiety, poor sleep, cramps
Individual r/Retatrutide posts, including cramps and fatigue at 4 mg

How much is known

Strong human trials

Phase 1, phase 2 (338 people) and five positive phase 3 trials, including TRIUMPH-1 (2,339 people) published in NEJM on 2026-09-29. Head-to-head trials against tirzepatide and semaglutide are running. Safety beyond about 2 years is unknown, and split dosing, sub-2 mg maintenance and cycling were never tested.