Retatrutide side effects: what the trials reported, dose by dose

The short answer: retatrutide causes the same kinds of side effects as approved GLP-1 drugs, mostly nausea, diarrhea, constipation, and vomiting, at somewhat higher rates on the top doses, plus two signals worth knowing about: an abnormal skin sensation called dysesthesia and a rise in heart rate. In the largest phase 3 trial, nausea affected 42.4% of people on the 12 mg dose versus 14.8% on placebo. [4]

Retatrutide is an investigational drug, not an approved one. Everything below comes from clinical trials, and most of the phase 3 figures are company toplines that have not yet been peer reviewed. This page tracks evidence. It does not give dosing advice.

What are the most common retatrutide side effects?

Gastrointestinal effects dominate every trial. In the phase 2 obesity trial of 338 adults, the most common adverse events were gastrointestinal, dose related, mostly mild to moderate, and partly reduced by starting at 2 mg instead of 4 mg. [1]

TRIUMPH-1, the pivotal phase 3 obesity trial with 2,339 participants, gives the clearest dose-by-dose picture. The figures are for 4 mg, 9 mg, and 12 mg, then placebo. [4]

Two things stand out. Nausea and vomiting climb with dose, and the 4 mg dose, which is reached with a single step up, had a lower discontinuation rate for adverse events than placebo. [4]

The type 2 diabetes trials show the same pattern at lower rates. In the 36-week phase 2 diabetes trial, mild to moderate gastrointestinal events occurred in 35% of people on retatrutide overall, ranging from 13% on 0.5 mg to 50% in one 8 mg group, versus 13% on placebo and 35% on dulaglutide 1.5 mg. [2] In TRANSCEND-T2D-1, a 40-week phase 3 trial in 537 adults, the most frequent adverse events were mild to moderate gastrointestinal events that subsided over time, and 2% to 5% stopped treatment for adverse events versus 0% on placebo. [3]

Retatrutide dysesthesia: the new skin signal

Dysesthesia means an abnormal sensation in the skin, such as tingling, burning, or pain to light touch. It is the one side effect that separates retatrutide's safety profile from the rest of the class so far. [4]

• TRIUMPH-1 (obesity): 5.1%, 12.3%, and 12.5% on 4, 9, and 12 mg versus 0.9% on placebo. [4]
• TRIUMPH-2 (obesity with type 2 diabetes): 4.5%, 5.6%, and 7.3% versus 0.7%. [5]
• TRIUMPH-3 (obesity with cardiovascular disease): 6.4% on both 9 and 12 mg versus 1.3%. [5]
• TRIUMPH-4 (obesity with knee osteoarthritis): 8.8% on 9 mg and 20.9% on 12 mg versus 0.7%. [6]

The company reports that these events were generally mild to moderate, that most resolved during treatment, and that most participants kept taking the drug. [4] Why it happens is not yet explained in a peer-reviewed paper.

Does retatrutide raise heart rate or blood pressure?

Heart rate goes up. In the phase 2 obesity trial, heart rate rose in a dose-dependent way, peaked at 24 weeks, and declined after that. [1] The glucagon receptor arm is the likely reason the rise is larger than with GLP-1-only drugs, and it is one reason regulators will look closely at the cardiovascular data.

Blood pressure moves the other way. In TRIUMPH-3, the 12 mg dose lowered systolic blood pressure by an average of 9.3 mmHg. [5] The retatrutide benefits post covers blood pressure, lipids, and liver fat in detail.

Retatrutide hair loss and fatigue

These are two of the most searched side effects, and the honest answer is that we do not yet have retatrutide-specific rates. The published abstracts and the company toplines we reviewed do not list hair loss or fatigue among the most common events, and full tables will come with the peer-reviewed papers.

The approved drugs in the class give a reference point. On the Zepbound label, hair loss occurred in 4% to 5% of people on tirzepatide versus 1% on placebo, and fatigue in 5% to 7% versus 3%, in weight management trials. [7] On the Wegovy label, hair loss occurred in 3% on semaglutide 2.4 mg versus 1% on placebo, and fatigue in 11% versus 5%. [8] Hair shedding after rapid weight loss is common with any method, which is why placebo-controlled rates matter more than anecdotes. See tirzepatide and semaglutide for their full label safety sections.

How many people stopped retatrutide because of side effects?

Discontinuation is the most practical safety number, because it counts people who could not continue. At the top 12 mg dose it ran higher than placebo in every obesity trial reported so far:

• TRIUMPH-1: 11.3% versus 4.9%. [4]
• TRIUMPH-2: 7.7% versus 4.9% (11.6% on 9 mg). [5]
• TRIUMPH-3: 13.5% versus 4.8%. [5]
• TRIUMPH-4: 18.2% versus 4.0%. [6]

For comparison, discontinuation for adverse events on approved tirzepatide in its weight management program was 10% versus 2% on placebo in one of the label's trials. [7] Different populations and durations make direct comparisons rough. Our tirzepatide vs retatrutide comparison sets the two programs side by side.

Is retatrutide safe?

"Is retatrutide safe" is a question the evidence cannot yet answer in full. Here is what is known and what is not.

Known: across phase 2 and phase 3, the side effect profile looks like other drugs with GLP-1 activity, plus dysesthesia and a heart rate rise. The type 2 diabetes phase 3 paper reported no severe hypoglycemia; two deaths occurred, both judged unrelated to the drug. [3]

Not yet known: long-term safety and hard cardiovascular outcomes. In TRIUMPH-3, cardiovascular events were rarer than expected in both arms. The hazard ratio for a five-part cardiovascular composite was 0.82 with a confidence interval of 0.55 to 1.22, and for the classic three-part composite it was 1.12 with an interval of 0.64 to 1.96. Both intervals cross no effect, so the trial neither shows benefit nor rules out harm. [5] A dedicated cardiovascular and kidney outcomes trial, TRIUMPH-Outcomes, is under way. [9]

Not reviewed: FDA has not evaluated the full safety file, because the drug has not been approved. Its status is logged on the retatrutide regulatory tracker.

Side effects of retatrutide sold online

Trial safety data apply to trial product, given under medical supervision with screening and monitoring. They do not apply to products sold online as retatrutide. FDA has warned companies that sold unapproved drugs containing retatrutide, falsely labeled "for research purposes" or "not for human consumption," directly to consumers with dosing instructions, and it urges consumers not to buy these products, which are of unknown quality. [10]

A 2026 case report shows what that can look like. A man with type 1 diabetes developed severe vomiting, diarrhea, high ketones, and acute kidney injury shortly after injecting an online product sold as retatrutide; a gut infection was also found, so the authors could not establish cause, but they flagged unknown composition and dosing as part of the risk. [11]

There is no lawful price for retatrutide today; see retatrutide cost. The only lawful way to receive it is a clinical trial, covered in how to get retatrutide.

What to do instead

If you are considering retatrutide because of weight or type 2 diabetes, approved options exist now with known label safety data. The GLP-1 hub lists every approved drug in the class, the obesity condition page grades the evidence, and how to get peptides prescribed explains the lawful prescription route. Clinics that list retatrutide under peptide therapy are selling an unapproved drug outside a trial. For side effects across the approved drugs, see GLP-1 side effects, ranked, and for trial status, where the retatrutide phase 3 program stands.