Mounjaro® Side Effects, Risks, and Safety
Key takeaways:
The most common Mounjaro® side effects are nausea, constipation, diarrhoea, and stomach pain.
These common gastrointestinal issues are usually temporary and improve as the body adjusts.
Serious side effects like pancreatitis or gallstones are rare but require but call for medical attention.
Always follow your prescriber’s treatment plan, review the patient information leaflet, and seek advice if symptoms persist.
If you’re taking Mounjaro® for type 2 diabetes or weight management in obesity, you may be wondering what side effects to expect.
Like all weight loss medications, Mounjaro® can cause both mild and more serious reactions. Fortunately, the most common side effects of Mounjaro® are typically temporary and improve with time.
Here’s everything to know about Mounjaro® side effects, including how long they last and when to seek medical advice.
What Is Mounjaro®?
Mounjaro® is a brand name for tirzepatide, a once-weekly weight loss injection and diabetes medication. It works as a dual GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) receptor agonist, mimicking hormones that regulate appetite and insulin production.
Mounjaro® can aid weight loss by:
Regulating blood sugar levels
Reducing appetite and cravings
Slowing down digestion
The Medicines and Healthcare products Regulatory Agency (MHRA) authorised Mounjaro® for weight management in adults as well as to treat type 2 diabetes.
Like other GLP-1 receptor agonists, such as semaglutide (found in Wegovy® and Ozempic®) or liraglutide (Saxenda®), Mounjaro® is most effective when used alongside lifestyle changes like healthy eating and physical activity.
In the United States, tirzepatide is also sold under the brand name Zepbound®. However, Zepbound® isn’t yet available in the United Kingdom.
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Common Side Effects of Mounjaro®
The most common side effects of Mounjaro® are digestive (gastrointestinal) issues, especially when starting treatment or increasing the dose. According to clinical trials, these side effects are usually mild to moderate and short-lived.
These common side effects include:
Nausea
Constipation
Diarrhoea
Vomiting
Fatigue
Headaches
Indigestion (dyspepsia)
Loss of appetite
Stomach pain
Bloating
Acid reflux or heartburn
Injection site reactions (like redness, swelling, or itching)
In general, higher doses of Mounjaro® are associated with more persistent or severe side effects.
How Long Will Mounjaro® Side Effects Last?
Most common side effects appear during the first few weeks of taking Mounjaro® or after a dose increase. They usually improve within a few days to weeks as your body adjusts to the medicine.
If symptoms are persistent or severe, your GP (general practitioner) or private healthcare professional may adjust your treatment plan or keep you on a lower dose for longer.
Serious Side Effects of Mounjaro®
Although rare, Mounjaro® can cause more serious side effects. Seek medical attention if you experience any of the following:
Increased heart rate (tachycardia). This is when your heart rate is too fast, typically over 100 beats per minute.
Inflammation of the pancreas (pancreatitis). Symptoms include severe stomach pain, vomiting, tenderness in the abdomen, and feeling generally unwell.
Gallbladder problems. This includes gallstones and inflammation of the gallbladder (cholecystitis). Symptoms may include upper-stomach pain, fever, yellow skin discolouration (jaundice), or nausea.
Low blood sugar (hypoglycaemia). This is more likely if Mounjaro® is used with insulin or sulfonylureas. Symptoms include dizziness, lightheadedness, sweating, confusion, or shakiness.
Severe allergic reaction (anaphylaxis). Symptoms include swelling of the face, lips, or tongue, difficulty breathing, or hives.
Kidney disease or acute kidney injury. This is usually linked to dehydration from vomiting or diarrhoea.
Thyroid cancer. Mounjaro® carries a boxed warning due to animal studies showing an increased risk of thyroid tumours, though this hasn’t been proven in humans. Warning signs would be a lump or swelling in the neck, a hoarse voice, difficulty swallowing, or shortness of breath.
If you notice any of these symptoms, stop taking Mounjaro® and seek immediate medical attention.
Mounjaro® is designated as a Black Triangle medicine in the U.K. This means it’s subject to additional monitoring to quickly identify any new safety information. You can report side effects through the MHRA Yellow Card scheme.
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Who’s Most At Risk of Mounjaro® Side Effects?
Mounjaro® isn’t suitable for everyone. People who fall into the following groups may have higher risks and should avoid the medication:
Anyone with a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2)
Those with a history of pancreatitis or severe gallbladder problems
People with uncontrolled gastrointestinal disease
People with severe kidney disease
People with type 1 diabetes
Mounjaro® is also not recommended during pregnancy or breastfeeding, as there’s not enough safety data in humans. If you’re pregnant, planning a pregnancy, or breastfeeding, ask your GP before starting or continuing treatment. You might also be required to be on contraception while taking the medicine.
Before starting a new medication, tell your prescribing provider about your medical history, including any health conditions you have. This helps them determine whether it’s safe for you to take.
Managing Mounjaro® Side Effects
Many side effects of Mounjaro® can be managed with simple lifestyle changes. Here’s what to try:
Eat smaller, more frequent meals to reduce Mounjaro® nausea and bloating.
Use non-prescription remedies for short-term relief of symptoms like heartburn, nausea, or constipation.
Avoid high-fat foods and alcohol, as they can worsen heartburn, nausea, and indigestion.
Stay hydrated by drinking plenty of water. Peppermint or ginger tea may also help with gastrointestinal side effects.
Consider using an electrolyte mix, especially if you’re experiencing diarrhoea or constipation.
If the injection site is sore, swollen, or itchy, use a cool compress.
If you find it difficult to manage your side effects, speak with your GP or private clinician who prescribed the medicine. They might adjust your dose schedule to give you more time to get used to the medication before moving on to a higher dose.
Alternatives to Mounjaro®
If you can’t tolerate the side effects of Mounjaro®, your GP or private prescriber might recommend another weight loss treatment.
Other options include:
Wegovy® (semaglutide), a once-weekly GLP-1 injection
Saxenda® (liraglutide), a daily GLP-1 injection
Xenical® (orlistat), an oral fat-blocking medication
No matter which weight loss medication you use, you’ll need to pair it with a healthy lifestyle to reach your weight loss goals. This includes eating a healthy diet, exercising frequently, managing stress, and getting enough sleep.
Mounjaro® Side Effects: In Summary
Mounjaro® is an effective medication for type 2 diabetes and weight management in obesity. But like all medicines, it can cause side effects. Here’s what you need to know:
The most frequent and common side effects are digestive issues like nausea, constipation, and diarrhoea, which usually improve as your body adjusts.
These typically go away after the first few days or weeks on tirzepatide and can often be managed with simple dietary changes or over-the-counter remedies.
Serious side effects — such as pancreatitis, gallstones, or severe allergic reaction — are rare but require immediate medical attention.
Always follow your healthcare professional’s guidance, attend regular monitoring appointments, and seek medical advice if you have concerns about side effects. Never stop taking prescribed medication without consulting your prescriber or GP first.
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FAQs
See answers to commonly asked questions about Mounjaro® side effects.
How long do Mounjaro® side effects last?
Most common side effects — like nausea or constipation — last a few days to weeks. These side effects are particularly common when you first start taking Mounjaro® or when you increase your dose. If your side effects persist or worsen, speak with your GP or private prescriber.
What are the most common side effects of Mounjaro®?
The most common side effects of Mounjaro® include nausea, constipation, diarrhoea, vomiting, stomach pain, bloating, and indigestion.
Can Mounjaro® cause serious side effects?
Yes, though they’re rare. Serious side effects include pancreatitis, increased heart rate, gallbladder problems, low blood sugar, kidney issues, and severe allergic reactions.
What should I do if I experience side effects of Mounjaro®?
Most mild side effects will go away over time. Gastrointestinal side effects, like Mounjaro® nausea, can usually be managed with non-prescription medication and at-home remedies. For serious or persistent side effects, consult your GP for medical advice. Report your side effects via the Yellow Card scheme.
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your GP about the risks and benefits of any treatment.