Retatrutide side effects and how often they happen

Retatrutide is a once-weekly injection that acts on the GIP, GLP-1 and glucagon receptors. Its most common side effects are gut effects, mainly nausea, diarrhea, constipation and vomiting. As a group they rise with the dose, and most are mild to moderate. Watch for three others as well. Heart rate goes up a little, some people get a skin sensation called dysesthesia, and blood pressure can drop at the higher doses.

Retatrutide side effects by dose

TRIUMPH-2, a phase 3 trial, gives the rates by dose. It ran for 80 weeks in 1,152 adults with type 2 diabetes and a BMI of 27 or higher.

TRIUMPH-2 came out in the Lancet on September 29, 2026. TRIUMPH-1 came out the same day in the New England Journal of Medicine. It enrolled 2,339 adults with obesity and no diabetes. Both trials gave 4, 9 or 12 mg once a week, or placebo, for 80 weeks. The TRIUMPH-1 report names gut effects as the most common side effects.

A third phase 3 trial, TRANSCEND-T2D-1, gave the same doses for 40 weeks to 537 adults whose type 2 diabetes was managed with diet and exercise alone. Its gut effects were mostly mild to moderate.

Gut effects and how people handle them

• What people notice. The usual ones are nausea, diarrhea, constipation and vomiting. They were the most common side effects in TRIUMPH-1, TRANSCEND-T2D-1 and the phase 2 obesity trial.
• They rise with the dose. The phase 2 obesity trial found them dose-related. In the phase 2 type 2 diabetes trial, 35% on retatrutide had them, against 13% on placebo and 35% on dulaglutide 1.5 mg. The lowest dose, 0.5 mg, matched placebo at 13%.
• A slower start helps. In the phase 2 obesity trial, starting at 2 mg instead of 4 mg cut gut effects somewhat.
• If they don't settle. In the TRIUMPH trials, a person first stepped down a dose and then back up. If gut effects or eating too little still did not improve, they could move to a lower dose for good.
• Eating enough. Everyone in the TRIUMPH trials got lifestyle counseling. It focused on healthy food and eating enough, with balanced meals, rather than cutting calories. It also asked for at least 150 minutes a week of moderate activity, including strength work.

When side effects start and when they settle

• Dose climb. The TRIUMPH trials reached each target dose on a fixed schedule over the first 16 weeks, then held it for 64 weeks. This slow climb is called Titration.
• Start speed. In the phase 2 type 2 diabetes trial, the highest rate of gut effects (50%) came in the 8 mg group that started at 4 mg rather than 2 mg.
• Weekly timing. The Half-life is about 6 days, which is why retatrutide is dosed once a week.
• Gut effects. They subsided over time in TRANSCEND-T2D-1.
• Heart rate. In the phase 2 obesity trial, the rise peaked at week 24 and then came down.
• Skin sensitivity. In 15 French safety reports on GLP-1 drugs, 10 of them on semaglutide, it began 3 to 93 days after the first injection, during the dose climb.

Heart rate

Retatrutide raises heart rate a little, and the rise tracks the dose.

• The rise. In the phase 2 obesity trial, heart rate by the end of the 48 weeks was up 1.7 bpm (beats per minute) at 1 mg, 3.1 at 4 mg, 4.8 at 8 mg and 6.0 at 12 mg. Placebo was up 0.4. The retatrutide groups started at averages of 69.3 to 71.1 bpm.
• Next to other GLP-1 drugs. A 2026 meta-analysis of trials in people without diabetes put the rise against placebo at 3.46 bpm for retatrutide, drawn from its one phase 2 trial. Separate trials gave 3.35 bpm for Semaglutide and 2.05 for Tirzepatide.
• What the trials watched. The TRIUMPH safety checks included pulse and ECGs (heart tracings).

Skin sensitivity (dysesthesia)

Dysesthesia is skin that burns, tingles or feels oversensitive to a light touch.

• How common. In TRIUMPH-2 it rose with the dose, at 4%, 6% and 7% on 4, 9 and 12 mg against 1% on placebo. In the phase 2 obesity trial, skin sensitivity and hyperesthesia (extra sensitivity to touch) reached 7% on retatrutide against 1% on placebo.
• Severity. In the phase 2 obesity trial it was mild to moderate, and nobody stopped over it.
• Where people feel it. In the 15 French safety reports on GLP-1 drugs, burning showed up mainly on the back, belly, thighs and arms. Tingling showed up mainly in the extremities.
• Stopping and restarting. In those reports it cleared after the drug was stopped. Where doctors ran a workup, the results were normal. In the three people who restarted, it came back at the same dose.
• Other drugs list it too. The EU product information for semaglutide's weight-loss version (Wegovy) and for tirzepatide (Mounjaro) lists dysesthesia.

Low blood pressure

Low blood pressure rose with the dose in TRIUMPH-2. It reached 1%, 5% and 6% at 4, 9 and 12 mg, against under 1% on placebo.

Sleep, mood and libido

Sleep problems, early waking around 2 to 4 am, anxiety and low libido are not among the common side effects in the trial summaries. The phase 2 obesity trial's posted results don't list them either. The TRIUMPH trials screened mood for depression and suicidal thoughts with two questionnaires, the Patient Health Questionnaire-9 (PHQ-9) and the Columbia Suicide Severity Rating Scale (C-SSRS).

Why people stopped

• TRIUMPH-2. 4% at 4 mg, 12% at 9 mg and 8% at 12 mg stopped for good over a side effect or death, against 5% on placebo. The 9 mg group had the most stops, not the 12 mg group.
• TRANSCEND-T2D-1. 2 to 5% on retatrutide stopped over side effects, against none on placebo.
• Deaths. TRIUMPH-2 recorded 6 deaths across the three retatrutide groups and 1 on placebo. The investigators judged none of them related to the drug.

Take care if

You have type 1 diabetes. A 2026 case report described a man with type 1 diabetes who had severe vomiting, high ketones and kidney injury two days after injecting a product sold as retatrutide. Nobody tested what the product contained. He had also missed insulin doses and had a confirmed Shigella gut infection, so the author could not establish the cause.

How it compares with tirzepatide

Tirzepatide shows the same pattern, led by gut effects. In its SURMOUNT-1 trial they came mainly during the dose climb. Over 72 weeks, 4.3 to 7.1% stopped over side effects across its three doses, against 2.6% on placebo. SURMOUNT-1 enrolled people without diabetes and counted side-effect stops only, so its rates don't line up one to one with TRIUMPH-2.

Common questions

How long after the first dose do side effects start? In the phase 2 type 2 diabetes trial, gut effects were most common in the group that started fastest. In TRANSCEND-T2D-1 they subsided over the weeks. In French safety reports on GLP-1 drugs, skin sensitivity began 3 to 93 days after the first injection. The trial summaries give no onset time in hours or days.

Does retatrutide raise resting heart rate, and does it settle? Heart rate rises with the dose. In the phase 2 obesity trial it peaked at week 24 and then declined. By the end of the 48 weeks it sat about 5 to 6 bpm above baseline at 8 and 12 mg.

What is skin dysesthesia, and how common is it? It is skin that burns, tingles or feels oversensitive to touch. In TRIUMPH-2 it affected 4 to 7% by dose, against 1% on placebo. In the phase 2 obesity trial, skin sensitivity and hyperesthesia reached 7% against 1%.

Why do some people wake at 2 to 4 am? Sleep problems are not among the common side effects in the trial summaries, so there is no trial figure for early waking.

Can retatrutide cause anxiety or low libido? The trial summaries and the phase 2 obesity trial's posted results don't list either among the common side effects. The TRIUMPH trials screened mood with the PHQ-9 and C-SSRS questionnaires.

Why did people stop at the 12 mg dose? In TRIUMPH-2, 8% at 12 mg stopped for good over a side effect or death, against 5% on placebo. The 9 mg group stopped most, at 12%. The published summary gives the stop rates but doesn't split them by cause.

Can you drink alcohol on retatrutide? In a 2026 rat study, one dose of retatrutide dulled the rats' ability to tell they had been given alcohol. Semaglutide and tirzepatide did the same. The authors read this as a change in how alcohol feels.