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Side Effects of Mounjaro

Applies to the Mounjaro injection and the Mounjaro pill: both contain semaglutide.

  • Gastrointestinal complaints are the most common and are usually mild
  • They mainly occur at the start and after a dose increase, and then decrease
  • Serious side effects are rare, but recognizable
When to call your doctor?
Mon–Fri 09:30 AM – 05:00 PM | Sat 09:00 AM – 03:00 PM
Nicolette Lammers
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The information on this page has been medically reviewed by

How often do Mounjaro side effects occur?

The package leaflet states how often each side effect occurs. Very common means in more than 1 in 10 users. Common means in 1 to 10 out of 100 users. Uncommon means in 1 to 10 out of 1,000 users. Rare means in 1 to 10 out of 10,000 users.

FrequencySide Effects
Very commonnausea, diarrhea, vomiting, constipation, abdominal pain
Commonheartburn, burping, flatulence, bloating, fatigue, dizziness, low blood pressure, hair loss, injection site reactions, increased heart rate
Uncommongallstones, cholecystitis, pancreatitis
Raresevere allergic reaction

In studies on weight loss in people without diabetes, participants received Mounjaro or a placebo, a substance without an active ingredient. Complaints also occurred in the placebo group. This shows what is caused by Mounjaro:

Side EffectWith MounjaroWith placebo
Gastrointestinal complaints (total)56 to 61%30%
Nausea25 to 33%10%
Diarrhea19 to 23%7%

Percentages vary by dose (5, 10 or 15 mg). Complaints were usually mild or moderate. Between 2 and 4% of participants stopped due to gastrointestinal complaints.

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When do side effects occur and how long do they last?

You start with 2.5 mg per week. The dose is then gradually increased, usually every four weeks. Side effects mainly occur during this build-up phase: at the start and after each increase, including the step to 5 mg. Nausea, vomiting and diarrhea are then more common and usually decrease again in most people in the following weeks.

If the complaints are too severe, your doctor may postpone an increase. The full dosing schedule and explanation of the pen can be found on the Mounjaro page.

Constipation can last longer than other gastrointestinal complaints. Tips on fiber can be found in our blog on psyllium fiber.

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Common Side Effects and what you can do about them

For each complaint, you can read how often it occurs, what helps, and when to contact your doctor.

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Common side effects

  • Nausea In 25 to 33% of cases, especially in the build-up phase. Helps: smaller meals, eating slowly, and limiting fat.

  • Diarrhea, vomiting, and dehydration Diarrhea in 19 to 23% of cases, vomiting very common. Drink small sips of water throughout the day.

  • Constipation Very common and can last longer. Helps: sufficient hydration, high-fiber foods, and daily exercise.

  • Heartburn, burping, and bloating Common, because your stomach empties slower. Helps: smaller meals and not eating right before bed.

For persistent complaints, your doctor can advise.

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Other complaints you might notice

  • Fatigue, dizziness, and headache Especially at the beginning, also due to eating and drinking less. Eat regularly and drink enough.

  • Hair loss Common, especially with rapid weight loss. Is usually temporary.

  • Itching or redness at the injection site In 8% (placebo 1.8%), usually mild. Change injection site every week.

  • Palpitations and a higher heart rate The heart rate increases by an average of 3 beats per minute (placebo less than 1).

  • Muscle pain Not listed in the package leaflet. May be related to rapid weight loss, insufficient protein or fluids, or increased exercise.

Read our blog about hair loss

If in doubt, discuss it with your doctor

Rare but serious side effects of Mounjaro

Serious side effects are rare. However, it is good to recognize the signs so that you can seek help in time.

Pancreatitis

Sign: severe, persistent abdominal pain, sometimes radiating to the back, with or without vomiting. Stop Mounjaro and contact a doctor immediately.

Gallstones and Cholecystitis

Sign: pain in the upper right abdomen, fever, or a yellow discoloration of the skin or eyes. Contact your doctor immediately.

Severe allergic reaction

Sign: swelling of the face, lips, tongue or throat, or difficulty breathing or swallowing. Call 112. If you experience itching or a rash all over your body, contact your doctor immediately.

Low blood sugar

If you also use insulin or a sulfonylurea derivative (certain diabetes tablets), your blood sugar may become too low. Signs include sweating, trembling, hunger, confusion, and palpitations. Your doctor can adjust the dosage of your other medication.

Eye problems in type 2 diabetes

In people with type 2 diabetes, a rapid improvement in blood sugar can temporarily worsen an existing eye condition caused by diabetes (diabetic retinopathy). If you have diabetic retinopathy, your doctor will have your eyes checked extra carefully. If you notice a sudden worsening of your vision, contact a doctor immediately.

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When should you contact your doctor?

Call 112 if you experience swelling of the face, lips, tongue or throat, or difficulty breathing or swallowing. Call your doctor immediately if:

  • Persistent, severe abdominal pain
  • Prolonged vomiting or diarrhea
  • A yellow discoloration of the skin or eyes
  • Sudden worsening of vision
  • No bowel movement for more than a few days
  • An injection site that becomes swollen, warm, or very painful
  • Palpitations at rest or a persistently high heart rate
Outside office hours: Emergencies

Pregnancy, contraception, and surgery

Mounjaro should not be used during pregnancy. If you wish to become pregnant, stop at least one month beforehand, as tirzepatide remains in the body for a long time. Use effective contraception during treatment.

Are you using the birth control pill? Mounjaro can reduce its effectiveness, especially in the first few weeks and after a dose increase, and also if you experience vomiting or diarrhea. Therefore, for the first 4 weeks after starting and after each dose increase, use an additional barrier method, such as a condom, or switch to a contraceptive method that is not taken orally.

Are you breastfeeding or planning to? Discuss with your doctor whether Mounjaro is suitable for your situation.

Do you need to undergo surgery or an examination with anesthesia or sedation? Always report that you are using Mounjaro. Because your stomach empties slower, there is a risk that stomach contents may enter your lungs.

Long-term side effects

Mounjaro has been studied in trials lasting up to approximately three years. The side effects observed in these studies are listed on this page. What happens after even longer use is not yet known. Therefore, Mounjaro is under additional monitoring: new reports of side effects are monitored with extra precision. This is also why it is important that side effects are reported.

If you stop Mounjaro, the side effects usually disappear. However, weight may return. That is not a side effect, but something to discuss with your doctor beforehand.

Does Mounjaro have more or fewer side effects than Wegovy or Ozempic?

Mounjaro, Wegovy, and Ozempic cause similar side effects, especially gastrointestinal complaints in the build-up phase. Mounjaro contains tirzepatide, while Wegovy and Ozempic contain semaglutide. Discuss with your doctor which medication is right for you. A detailed comparison can be found in our blog about the difference between Mounjaro, Wegovy, Ozempic, and Saxenda.

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Reporting Side Effects and guidance

If you experience side effects, always discuss them with your doctor. You can also report side effects yourself to Lareb, the Netherlands Pharmacovigilance Centre. At The Body Clinic, the doctor discusses side effects during check-ups. Where necessary, the doctor adjusts the dose escalation or advises supportive medication for the stomach or bowel movements.

If you have questions about your own complaints, please contact your treating doctor.

Frequently Asked Questions about side effects 

Do you have a question about your own complaints? Contact your treating physician.

  • Most gastrointestinal complaints occur during the titration phase and decrease in the following weeks for most people. They may temporarily return after a dose increase. Constipation can persist longer.

  • Eat smaller meals, eat slowly, and stop as soon as you are full. Limit fatty and fried foods and drink enough water throughout the day. If the nausea remains severe, contact your doctor. Read more tips in our blog about GLP-1, nausea and digestion.

  • Hair loss is common, especially with rapid weight loss, and is usually temporary. Eat enough protein and discuss it with your doctor if you are concerned.

  • Mounjaro can slightly increase your heart rate, by an average of 3 beats per minute. If you notice heart palpitations at rest or if your heart rate remains unusually high, please contact your doctor.

  • Alcohol can worsen nausea and other gastrointestinal complaints. If you also use insulin or certain diabetes tablets, alcohol increases the risk of low blood sugar. Therefore, be careful, especially during the dose escalation phase, and discuss it with your doctor.

  • Not without consulting your doctor. Many side effects diminish after the titration phase, and your doctor may adjust the dosage. However, stop immediately and contact a doctor if you experience severe, persistent abdominal pain. Call 112 (or your local emergency number) if you have swelling of the face or throat, or difficulty breathing.

  • In studies, gastrointestinal complaints were slightly more common with 10 mg and 15 mg than with 5 mg. Complaints mainly arise shortly after an increase, for example, from 2.5 mg to 5 mg. Your doctor may postpone an increase if the complaints are too severe.

  • Mounjaro has been studied in trials lasting up to approximately three years. No side effects other than those listed on this page were observed in these studies. What happens after even longer use is being further monitored: the drug is under additional monitoring.