Mounjaro side effects

What are the most common side effects of Mounjaro?

The FDA label gives a pooled table from two of the weight trials (one with participants without diabetes, one with participants with type 2 diabetes; treatment up to 72 weeks). The rates below are side effects that occurred more often than with placebo and in at least 2%. ^[3]

The SmPC (Turkish KÜB) gives the same side effects with frequency classes. Very common (more than 1 in 10 people): nausea, diarrhea, vomiting, abdominal pain, constipation and hypoglycemia when used with a sulfonylurea or insulin. Common (1–10 in 100 people): hypersensitivity, dizziness, low blood pressure, dyspepsia, abdominal distension, belching, gas, reflux, hair loss, fatigue, injection site reactions, increased heart rate, and raised lipase, amylase and calcitonin. Uncommon (1–10 in 1,000 people): gallstones, gallbladder inflammation, acute pancreatitis, delayed gastric emptying, taste disturbance. Rare: anaphylaxis and angioedema (post-marketing reports). ^[1]

According to the SmPC, in the weight trial in people without diabetes, digestive side effects were mostly mild (60.8%) or moderate (34.6%) in severity; nausea, vomiting and diarrhea were more frequent during dose escalation and declined over time. ^[1]

Do many people stop the drug because of side effects?

Discontinuation rates vary by trial and patient group; the table below ties each figure to its own trial.

In the pooled data of placebo-controlled trials in adults with diabetes, discontinuation because of digestive side effects alone was 3.0%, 5.4% and 6.6% at 5, 10 and 15 mg, and 0.4% with placebo. ^[1]

What are the serious side effects and warnings?

Pancreatitis

Acute pancreatitis has been reported in tirzepatide users and is among the uncommon side effects in the SmPC. The drug has not been studied in people with a history of pancreatitis; it is stopped if pancreatitis is suspected and not restarted if the diagnosis is confirmed. A rise in pancreatic enzymes alone, without other findings, is not considered an indicator of pancreatitis. ^[1] According to the FDA label, in the diabetes trials, adjudication-confirmed acute pancreatitis was 0.23 per 100 patient-years in tirzepatide users and 0.11 with comparators; in the weight trials the rates were 0.2% in both arms. Post-marketing reports also include fatal hemorrhagic and necrotizing pancreatitis. ^[3]

Gallbladder

In the pooled weight analysis in the FDA label, gallstones were reported in 1.1% of tirzepatide users and 1% with placebo; gallbladder inflammation in 0.7% versus 0.2%; gallbladder surgery in 0.2% versus 0%. Acute gallbladder events were associated with weight loss. ^[3]

Hypoglycemia

Marked hypoglycemia is rare when tirzepatide is used alone; the risk increases with a sulfonylurea or insulin. According to the SmPC, clinically important (blood glucose below 54 mg/dL) hypoglycemia or hypoglycemia requiring the help of another person occurred in 10–14% of patients when tirzepatide was added to a sulfonylurea and 14–19% when added to basal insulin. In the weight trial in people with type 2 diabetes, this rate was 10.3% in those using a sulfonylurea and 2.1% in those not using one. ^[1]

Fluid loss and kidney

Nausea, vomiting and diarrhea can cause fluid loss, which can lead to worsening of kidney function up to acute kidney failure; the SmPC asks that this be taken into account particularly in older people. ^[1] In the pooled weight analysis in the FDA label, acute kidney injury was reported in 0.5% versus 0.2%. ^[3]

Thyroid

In a two-year study in rats, tirzepatide increased thyroid C-cell tumors (adenoma and carcinoma); the significance in humans has not been determined. The FDA gives this as a boxed warning, considers the drug contraindicated in personal or family history of medullary thyroid carcinoma and in MEN 2, and states that the value of routine calcitonin or ultrasound monitoring for early detection is uncertain. ^[3] The Turkish SmPC also lists the same two conditions as contraindications; it lists raised blood calcitonin as a common finding in weight trials. ^[1]

Anesthesia, retinopathy and allergy

• Cases of aspiration into the lungs during general anesthesia or deep sedation have been reported in GLP-1 receptor agonist users. The FDA states that the data are insufficient to say whether changing the preoperative fasting period or pausing the drug reduces this risk. ^[3]
• According to the EMA product information, rapid improvement in blood glucose has been associated with temporary worsening in diabetic retinopathy. ^[2]
• Anaphylaxis and angioedema have been reported rarely after marketing. ^[1]

Does Mounjaro cause hair loss?

According to the FDA label, hair loss in tirzepatide users was associated with weight loss. In the pooled analysis it was reported in 7.1% of women and 0.5% of men; with placebo these rates were 1.3% and 0%. No tirzepatide user stopped treatment because of hair loss; one person in the placebo arm stopped. ^[3] The Turkish SmPC lists hair loss as a common side effect seen mainly in patients with overweight and obesity. ^[1]

How much muscle is lost?

When weight is lost, not only fat but also lean mass decreases. In the body composition substudy of SURMOUNT-1, DXA measurement was made at baseline and at week 72 in 160 participants. In tirzepatide users, weight decreased by 21.3%, fat mass by 33.9% and lean mass by 10.9%; with placebo these values were 5.3%, 8.2% and 2.6%. In both groups about 75% of the weight lost was fat and 25% lean mass; the proportions were largely similar by sex, age and amount of weight loss. ^[5]

The limits of these data are important: the aim of the substudy was to measure body composition by DXA, and muscle strength or physical function was not the subject of this analysis; 73% of participants were women and among the authors are employees of the drug’s manufacturer. ^[5]

Mood and suicidal thoughts: what is the current situation?

On January 13, 2026, the FDA requested the removal of the warning on the risk of suicidal thoughts and behavior in GLP-1 receptor agonists from the Saxenda, Wegovy and Zepbound labels. In the agency’s assessment, after confounding factors were balanced, no increase in the risk of intentional self-harm was found in GLP-1 receptor agonist users compared with SGLT2 inhibitor users; the body of published observational and pooled studies did not support a causal relationship. ^[7] This does not mean that the situation of people who experience mood changes is unimportant; it only states that a causal link with the drug has not been shown.

Is there a risk of vision loss (NAION)?

In June 2025, the EMA’s safety committee PRAC decided that non-arteritic anterior ischemic optic neuropathy (NAION), an eye disease that can cause sudden vision loss, is a very rare (up to 1 in 10,000 users) side effect of semaglutide. ^[8] This decision covers only medicines containing semaglutide. NAION does not appear in the side effect lists of the 2026 EU, US and Türkiye tirzepatide product information. ^{[2] [3] [1]} This does not mean the risk has been excluded for tirzepatide; it shows that the matter has not been brought to a regulatory conclusion for tirzepatide.

What is not known in the long term?

The longest placebo-controlled data are the 176-week treatment of participants with prediabetes in SURMOUNT-1; the authors report that no new safety signal was seen in this period and that the most frequent adverse events (other than COVID-19) were digestive side effects. ^[6] Beyond this, the following are open questions:

• The risk of medullary thyroid carcinoma in humans (the relevance of the rat finding to humans has not been determined). ^[3]
• The consequences of use in pregnancy: human data are insufficient, and animal studies have shown reproductive toxicity. ^[1]
• The long-term significance of antibodies: according to the SmPC, antibodies against the drug developed in 60.6–65.1% of patients in the weight and sleep apnea trials; the SmPC states that no evidence of an effect on pharmacokinetics, efficacy or safety was seen. ^[1] According to the FDA label, however, hypersensitivity reactions (6.2% versus 3%) and injection site reactions (11.3% versus 1%) were more frequent in those who developed antibodies. ^[3]
• The effect on lean mass with use lasting years: body composition data are limited to 72 weeks. ^[5]

Pregnancy and product reliability

According to the Turkish SmPC, use of tirzepatide is not recommended in pregnancy and in women of childbearing potential not using contraception; if pregnancy is planned or occurs, the drug is stopped and, because of its long half-life, it is stopped at least 1 month before a planned pregnancy. In breastfeeding, the decision is made by weighing benefit and risk together. ^[1]

The side effect frequencies on this page belong to trials conducted with licensed products. In Türkiye, a letter from the Erzurum Provincial Health Directorate to the pharmacists’ chamber (chamber registration date May 20, 2026), referring to the TİTCK (Turkish Medicines and Medical Devices Agency) letter dated May 14, 2026, relays that reports of suspected counterfeiting of medicines containing GLP-1 receptor agonists have increased markedly; in pharmacy and pharmaceutical warehouse inspections, Ozempic, Saxenda and Wegovy products and Mounjaro solution for injection are stated to carry a high counterfeit risk. The letter emphasizes that medicines should not be bought over the internet and that medicines that cannot be registered in the Medicine Track and Trace System (İTS) should not be kept or used. ^[10]

Limits of this page

This page summarizes side effects reported in product information and trials; it does not predict which side effect will be seen in individual people. According to the FDA label, severe and persistent abdominal pain that may radiate to the back may be a sign of pancreatitis, and a mass in the neck, difficulty swallowing, shortness of breath or persistent hoarseness may be a sign of a thyroid tumor; in a serious allergic reaction, medical help is needed immediately. ^[3] The SmPC emphasizes that fluid loss due to nausea, vomiting and diarrhea can impair kidney function. ^[1]