Mounjaro side effects guide and how to manage them

Written by

Jaanki Kotecha

Last reviewed

March 1, 2026

Reviewed by

Jaanki Kotecha

Next review

January 23, 2027

Unsure about the immediate and long-term side effects of Mounjaro? This handy guide gives you a good understanding of the most queried symptoms – from mild reactions to those that might need more attention. Get to know what to look out for so you feel confident and prepared on your weight loss journey.

What are the most common Mounjaro side effects?

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Reduction in appetite

Mounjaro does suppresses your appetite. It works by stimulating two hormone receptors: glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). GLP-1 helps regulate blood glucose levels by slowing down the emptying of the stomach to keep hunger at bay. GIP enhances the effects of GLP-1 by regulating the energy balance in your brain and fat cells. This is an intended effect of Mounjaro and is a contributing factor to weight loss.

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Nausea

Nausea is a common side effect of Mounjaro. In research trials, 1 in 5 Mounjaro users reportedly experienced nausea. tirzepatide (the active drug in Mounjaro) slows down gastric emptying, which can lead to feelings of fullness and discomfort, especially when starting treatment or increasing doses.

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Diarrhoea

Diarrhoea is another common side effect of Mounjaro, reported by approximately 16% of users during clinical trials. This is due to the impact of tirzepatide on gastrointestinal motility (the movement of food through the digestive tract) and digestion. While not everyone experiences diarrhoea, it can occur, particularly during the initial weeks of treatment as your body adjusts.

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‍Vomiting

Vomiting is a reported side effect of Mounjaro, although it’s less common than nausea, with approximately 9% of users reported sickness during treatment. It’s typically associated with higher doses or rapid dose escalation and may accompany nausea in some cases. Eating smaller meals throughout the day and avoiding greasy, fried foods can help keep nausea and vomiting at bay.

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Constipation

Constipation is another side effect of Mounjaro, reported in around 5–10% of patients (depending on dose), although it’sless common than diarrhoea. Constipation can occur because of delayed gastric emptying caused by the medication. Increasing your fibre intake alongside getting enough fluid (2-3 litres per day) helps reduce this symptom.

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Stomach pain

Stomach pain or abdominal discomfort is a potential side effect of Mounjaro, as well as indigestion (a feeling of discomfort or fullness in the upper abdomen). Around 7% of users reported stomach pain (dyspepsia) during clinical trials. It may be related to nausea, slowed gastric emptying, or other gastrointestinal effects of the drug.

Most gastrointestinal side effects like nausea, diarrhoea, and reduced appetite, tend to decrease over time as the body adjusts to the medication. If these symptoms persist or get worse, speak to a member of our clinical team who’ll help you manage symptoms or adjust your dose..

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Insomnia

You may have heard about people experiencing insomnia as a result of taking Mounjaro and other weight loss medications. But it’s not listed as a common side effect by the manufacturer.

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Hair loss

Research shows that hair loss can be a possible side effect of taking Mounjaro. A meta-analysis performed on eight studies found that, in one of those studies, approx. 5.2% of participants experienced hair loss due to tirzepatide (the active drug in Mounjaro). However, this may not be directly related to tirzepatide, . Increased hair shedding can be common with significant changes in caloric intake. Eating nutrient-dense foods can help reduce hair loss, particularly protein, healthy fats and the micronutrient biotin also known as vitamin B7.

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As a Phlo Clinic patient, you will receive a full Nutrition Guide written by our Obesity Specialist Dietitian

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Sulphur Burps

Excessive burping can be unpleasant but can be common when taking a medication that affects the digestive system. Mounjaro is a glucagon-like peptide-1 (GLP-1) agonist, which means it binds to and activates GLP-1 receptors,mimicking the effects of the natural GLP-1 hormone. This hormone slows down gastric emptying, which causes food and liquid to stay in the stomach longer and can increase the amount of gas created. When food or other substances in your stomach are broken down, the fermentation created bybacteria can produce sulphur-containing gases, leading to burps.

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Sensitive taste buds

Some people claim that taking Mounjaro affects their taste. This has been reported but isn’t a common side effect. Taste is a subjective sense that varies depending on the individual, so what one person experiences may not be the case for another.

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Acid reflux (heartburn)

The Mounjaro injection can cause acid reflux (heartburn) for some people. This can be due to excess stomach acid build-up which occurs because of delayed gastric emptying. Avoiding trigger foods such as spicy dishes, citrus fruits, caffeine and alcohol, and eating smaller, more frequent meals can help alleviate discomfort.

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Dry mouth

Some people experience dry mouth as a side effect of taking Mounjaro, often linked to eating and drinking less. This is a result of a change in appetite and fluctuating blood glucose levels leading to less lubrication in the mouth, or acid reflux. You can prevent dry mouth by drinking plenty of fluids and avoiding diuretics like alcohol and caffeine that may dehydrate you further.

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Dizziness

Dizziness is a known side effect of taking this medication. Mounjaro works by mimicking the hormones GLP-1 and GIP, which stimulate the release of insulin from the pancreas after a meal. This insulin works to regulate your blood glucose levels. It’s well-known that not eating and drinking enough can lead to feelings of dizziness. Speak to one of our expert clinical team if you’re experiencing frequent dizziness as a result of taking Mounjaro to avoid self-diagnosis.

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Headaches

Headaches have been anecdotally reported as a side effect of Mounjaro. Changes in food and liquid intake, as a result of taking Mounjaro, may cause dehydration-related headaches. Headaches can also be a symptom of low blood glucose levels. Speak to our expert clinical team if you’re experiencing consistent headaches while taking Mounjaro.

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Tired/Lethargy

Some people feel more tired, lethargic and weak while adjusting to eating less, particularly in the early weeks of weight loss treatment. Tirzepatide, the active ingredient in Mounjaro, works by suppressing your appetite, which may lead to consuming less calories than you’re used to. As your body adjusts to a lower calorie intake, you can feel tired. Make sure you’re consuming nutrient-dense foods and protein to meet your body’s energy needs. As you get used to your new medication, your body may go through an adjustment period, of which tiredness can be a side effect. Make sure you speak to one of our expert clinical team if you’re concerned about your energy levels.

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Pancreatitis

Pancreatitis is a possible side effect of Mounjaro. However, this risk is generally considered rare. Mounjaro may increase enzyme activity in the pancreas, which could, in very rare cases, lead to inflammation. Also, if you have gallstones, Mounjaro can also slightly increase your risk of developing gallstone-related issues such as gallstone pancreatitis. If you're using Mounjaro and develop signs of pancreatitis, such as severe abdominal pain (especially radiating to the back), nausea, vomiting, or a fever, you must seek medical attention immediately.

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Muscle loss

Experiencing muscle loss when losing weight is normal. To reduce this, , make sure you’re eating regular meals and snacking on high protein foods. Resistance or strength training also helps to build and maintain your muscle mass during weight loss.

Remember, Mounjaro’s side effects vary from person to person with many not experiencing any at all. Whether you want to start your weight loss journey or have questions about the symptoms you’re experiencing, our expert clinical team are here to listen and support you, every step of the way.

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