Mounjaro side effects

According to the patient information leaflet that comes with your medication, the side effects when taking Mounjaro (tirzepatide) for weight loss include:

Very common side effects

• feeling sick (nausea)
• being sick (vomiting)
• diarrhoea
• constipation
• stomach pain

These side effects may affect more than 1 in 10 people but usually aren’t severe. If they become severe, speak to your doctor straight away. They may recommend stopping treatment, especially if you’re at risk of dehydration or severe constipation.

Common side effects

• allergic reactions (hypersensitivity), such as eczema, rash or itching
• dizziness
• low blood pressure (hypotension)
• stomach pain
• indigestion
• burping
• gas
• bloating of the stomach
• heartburn or reflux (gastroesophageal reflux disease or GORD/GERD)
• hair loss
• tiredness
• skin sensitivity, injection site reactions, such as redness or itching
• increased levels of certain pancreatic enzymes, such as lipase, in the blood
• increased levels of calcitonin in the blood
• gallstones - most of the time these are symptomless, but speak to your doctor if you experience sudden, severe stomach pain that lasts longer than a few hours or a few minutes alongside feeling confused, having a fever, and/or chills
• low blood sugar

These side effects may affect up to 1 in 10 people taking Mounjaro injections. If you get any of these side effects and they aren’t getting better after a few weeks, or become severe, speak to your doctor straight away.

Uncommon side effects

• fast pulse
• an increased levels of certain pancreatic enzymes, such as amylase, in the blood
• gallstones – most of the time gallstones don’t cause symptoms until they cause a blockage. Symptoms of a blockage include sudden and severe stomach pain that can last a few hours or a few minutes and confusion, fever, and chills
• pain at the injection site
• an increased level of calcitonin in the blood
• cholecystitis (infection of the gallbladder) – symptoms include a sudden sharp pain in the upper right side of your stomach that may spread towards your shoulder, fever and jaundice
• change in sense of taste
• skin sensation changes, skin sensitivity
• delay in the emptying of the stomach

These side effects may affect up to 1 in 100 people and can be more serious, so if you get any of these, speak to your doctor straight away. If you think you’ve got gallstones or cholecystitis and can’t get in touch with your GP, call 111 or get to A&E, as these usually need to be treated at the hospital.

Serious side effects

• Uncommon (may affect up to 1 in 100 people): An inflamed pancreas (acute pancreatitis) which can cause long-lasting and severe pain in the stomach and back.
• Rare (may affect up to 1 in 1,000 people): A severe allergic reaction (anaphylaxis or angioedema) which can cause problems breathing, swelling of the face and lips, and difficulty swallowing.

See a doctor straight away or go to A&E if you think you’ve got an inflamed pancreas.

Studies into taking the highest maintenance dose of Mounjaro (15mg) for 72 weeks didn’t find any negative long-term side effects. In fact, the long-term effects of taking Mounjaro (tirzepatide) included:

• reduced blood pressure for those with high blood pressure
• weight loss
• lower blood glucose (sugar) levels in people with type 2 diabetes

Still, some side effects may cause long-term health problems if not addressed early, including:

• acute pancreatitis – Although this can be treated, studies into acute pancreatitis show that around 25% of people may get it again. Your doctor may suggest that you stop taking Mounjaro if you get pancreatitis while taking it to prevent this.
• dehydration caused by severe vomiting and diarrhoea – If you get these symptoms, drink lots of fluids and speak to your doctor, especially if it lasts more than 48 hours. Being dehydrated could impact how well your kidneys work and in severe cases, may cause kidney failure.

Awareness of Mounjaro side effects, cancer, and long-term health is important. Some reports online state that Mounjaro may pose a risk of developing thyroid cancer. In human clinical trials, cancer has not been found to be a side effect of taking Mounjaro.

These claims come from a study of tirzepatide on male and female rats over 2 years. This study found that tirzepatide, when injected twice weekly in rats, caused an increase in thyroid C-cell tumours (adenomas and carcinomas) in all doses. It’s important to note here that rats are highly susceptible to developing cancers and tumours and this doesn’t mean that humans taking Mounjaro are necessarily at an increased risk of cancer.

In another 6 month study on mice with twice-weekly tirzepatide injections, there were no cases of thyroid C-cell hyperplasia (an abnormal change of cells) or neoplasia (abnormal growth of cells).

In other studies, like one investigating tirzepatide and cancer rates, Mounjaro and other GLP-1 receptor agonists have been linked to a reduction in some cancers, especially ones linked to high blood glucose levels, diabetes and obesity.

You should not take tirzepatide (Mounjaro) if you don’t meet the prescribing requirements, which is either a body mass index (BMI) of:

• 30 or more (obesity), or
• at least 27 but less than 30 (overweight) and one or more weight-related health problems, including prediabetes, abnormal levels of fats in the blood, high blood pressure, obstructive sleep apnoea, or a history of stroke, heart attack or blood vessel problems

➤ If you’re unsure what your BMI is, use our free BMI calculator to check your eligibility.

You also should not take it if you are:

• allergic to tirzepatide, or any other ingredients in the Mounjaro pen
• pregnant or planning to become pregnant
• breastfeeding
• under 18

Some health conditions could impact your use of Mounjaro, but your doctor may decide it’s still safe with closer monitoring. This depends on the severity of your condition and includes:

• severe problems with digesting food or food remaining in your stomach for longer, such as severe gastroparesis – it’s unlikely that you’ll be able to use Mounjaro as it could worsen these conditions.
• pancreatitis – if you’ve had it in the past and it’s never re-occurred, your doctor may decide it’s safe with closer monitoring. If you’ve had it very recently or have chronic pancreatitis, Mounjaro may not be suitable.
• certain eye problems, such as diabetic retinopathy or macular oedema – Mounjaro could worsen these conditions, so your doctor will let you know whether Mounjaro is suitable depending on the severity of your eye condition.
• type 2 diabetes – some medications that are regularly taken for blood sugar regulation, such as sulphonylurea or insulin, when taken alongside Mounjaro could cause low blood sugar (hypoglycaemia). Your doctor may want to change the doses of your other medications before starting Mounjaro, alongside closer blood sugar monitoring.
• liver or kidney disease – Mounjaro injections also contain benzyl alcohol*, which, in large amounts, can build up in your system and cause metabolic acidosis (too much acid in your body).

*Benzyl alcohol can also cause allergic reactions.

Most Mounjaro side effects start when you first begin your treatment. As you follow the Mounjaro dosage schedule and increase your dose.

You may also experience side effects when your dose is increased, as your body needs to get used to a higher dose of the medication.

Note that some side effects can also start at any time, such as injection site pain (uncommon), gallstones (uncommon) and an increased level of pancreatic enzymes in the blood (common).

Most Mounjaro side effects last a few days to a few weeks. You should let your doctor know straight away if your side effects are getting worse instead of better, are severe, or are affecting your daily life and preventing you from doing your normal activities. If they’re tolerable, there are ways to manage most side effects at home.

➤ Click here to find more information on managing Mounjaro side effects.

Most of the time, Mounjaro side effects will go away and get better on their own. In some patients, side effects go away when staying at a lower dose, so your doctor may recommend this. Although it’s not common, some patients don’t tolerate Mounjaro and need to switch to another weight loss medication.

If you get Mounjaro side effects, this doesn’t mean you can’t tolerate the medicine. More than 1 in 10 people may get very common side effects, like nausea or diarrhoea.

Luckily, there are ways to manage side effects at home so they don’t interfere with your daily life too much.

Knowing how to manage Mounjaro side effects can help you get past them, so you can continue with your treatment and reach your weight loss goals.

Very common side effects

Mounjaro stomach pain

For Mounjaro stomach pain relief, try:

• eating a balanced, healthy diet
• avoiding foods that could be triggering, such as oily, greasy, acidic, spicy, or rich meals
• eating little and often, instead of eating a lot at once
• using a hot water bottle or painkillers to help with the pain
• speaking with a pharmacist about other treatments that may help, as stomach pain could be caused by nausea or acid reflux

Stomach pain shouldn’t last long with Mounjaro and could be caused by other side effects.

If you get severe stomach pain that isn’t going away, it could be a sign of something more serious, such as pancreatitis. Speak with your GP, call 111, or go to A&E if your stomach pain is severe and long-lasting.

Mounjaro diarrhoea

Diarrhoea can be treated by:

• drinking plenty of fluids (mainly water or electrolyte drinks like Diarolyte)
• avoiding spicy, rich, fatty, and greasy foods
• avoiding caffeine, pure fruit juices, or alcohol (these could have laxative effects)
• using over-the-counter medicine, such as loperamide – most people only need it for 1 or 2 days and you shouldn’t take it for longer than 48 hours without speaking to your doctor
• resting and not over-exerting yourself

When you start to feel better, eat small portions of plain food and slowly introduce foods back if you don’t get more diarrhoea. Re-introducing food too quickly may upset your stomach, so take it slow. Just keep hydrated, as severe or long-lasting diarrhoea can cause dehydration. If you get severe diarrhoea, speak to your doctor.

Mounjaro sickness

This is a term used to cover Mounjaro nausea and Mounjaro vomiting, which are mainly treated the same way.

Nausea and vomiting can be treated by:

• drinking small amounts of fluid often (mainly water or electrolyte drinks)
• eating small, plain meals, if you can
• avoiding rich, fatty, or greasy foods
• avoiding caffeine, sugary drinks, or alcohol
• avoiding smoking, if you smoke, especially on an empty stomach
• getting fresh air
• resting
• distracting yourself when you feel nauseous to try and get your mind off of it, such as reading or watching your favourite TV show
• using over-the-counter or prescription medicines, such as anti-sickness tablets, after speaking with a pharmacist or doctor
• taking your Mounjaro dose with food, as this may alleviate some of the symptoms

As with diarrhoea, introduce foods back slowly as you start to feel better. Severe vomiting can cause dehydration, so speak to your doctor if you’re being sick frequently and can’t keep anything down.

Mounjaro constipation

Constipation can be treated by:

• eating little and often, so you aren’t putting too much into your stomach at once if you already feel uncomfortable
• eating a healthy, balanced diet
• avoiding alcohol
• choosing high-fibre foods or foods that may act as a natural laxative, such as broccoli, dried fruit, carrots or beans
• trying a stool softener or laxative which can be found over the counter
• doing stretches or other gentle exercises like walking
• trying to use a low stool while on the toilet, and if possible, raising your knees above your hips

If your constipation isn’t getting better with lifestyle changes and treatment, speak to your doctor. Severe constipation (not being able to pass a stool for longer than 3 days) can be painful and you may need prescription laxatives or another medication to help.

In rare cases, bowel obstruction could occur. This is a medical emergency and you should call 999 straight away. Symptoms include bloating, stomach pain, cramping, swelling, vomiting, difficulty passing gas, fever and loss of appetite.

Common side effects

Mounjaro burping

Burping can be treated by:

• not eating too quickly
• not using a straw or smoking, if you smoke (these can cause more air to enter your stomach)
• avoiding alcohol or fizzy drinks
• avoiding high-sugar, high-fat, or greasy foods
• drinking plenty of water
• trying mild to moderate exercise like walking, jogging, or yoga
• drinking herbal teas, such as peppermint
• taking Mounjaro with food
• using an over-the-counter remedy for indigestion, as this could be causing the gas in your stomach

Burping a lot on Mounjaro could be a sign of indigestion, heartburn, or acid reflux. Some people get sulphur burps or ‘eggy burps’ when taking Mounjaro. If you keep burping or get eggy burps, and it keeps happening, speak to your pharmacist or doctor about a treatment for reflux that can be taken alongside Mounjaro. It may also help to keep a food diary, so you can see if any foods worsen your symptoms.

Mounjaro heartburn or reflux

Heartburn or reflux (GORD or GERD) can be treated by:

• eating small, more frequent meals
• avoiding foods and drinks that trigger your symptoms, which may include caffeine, alcohol, and spicy, fatty, acidic, or greasy foods
• sleeping with your head slightly raised (to stop acid travelling back up)
• avoiding laying down after eating or eating close to bedtime
• eating your food slowly and chewing thoroughly
• wearing comfortable, loose clothes
• stopping smoking, if you smoke
• trying an over-the-counter acid reflux or heartburn medication

If your symptoms don’t get better and you’re taking over-the-counter medication every day, speak with your doctor. They may prescribe a different treatment that could help more.

Mounjaro tiredness

Mounjaro may cause tiredness by itself, or other side effects may make you feel tired, especially if they’re preventing you from getting quality sleep.

Tiredness can be treated by:

• maintaining a healthy, balanced diet with plenty of nutrients
• taking multivitamins if you’re not getting all the nutrients you need from your diet and are deficient
• staying hydrated
• getting regular exercise – even though it’s hard to exercise when you feel tired, do what you can, as exercising can improve your energy levels
• maintaining a good sleep schedule (at least 8 hours each night)
• cutting down on screen time close to bed
• limiting caffeine intake, especially after midday
• avoiding alcohol
• getting plenty of rest in the day if you’re feeling run down, especially if you have other side effects

If you keep feeling tired on Mounjaro, speak with your doctor. They may want to check this isn’t caused by a lack of certain vitamins or minerals, such as Vitamin D or iron.

You can also feel tired when eating less, exercising more, and changing your diet, so being tired could be caused by these lifestyle changes.

Mounjaro dizziness

Dizziness can be treated by:

• drinking plenty of fluids
• lying down until it passes, then getting up carefully and slowly
• avoiding driving or using heavy machinery if you feel dizzy to prevent accidents
• getting enough rest
• avoiding stressful situations and finding ways to reduce your stress levels, as this could be contributing to your dizziness
• taking Mounjaro after food and drink, especially if you get dizzy right after your injection

Mounjaro is most likely to cause dizziness if your blood sugar levels are low (hypoglycaemia), although you can get dizziness as a side effect with normal blood sugar levels. If you get dizziness when taking Mounjaro, especially if you have other symptoms like headache, weakness, or irritability, speak with your doctor so they can check your levels. People with type 2 diabetes should take special care, as Mounjaro can increase the risk of hypoglycaemia if taken with insulin.

Mounjaro injection site reaction

A 2025 report has found that Mounjaro skin sensitivity is more common in recent studies, typically because of injection site reactions. Although it is less common compared to other side effects and occurs at a lower rate. These reactions can happen as minor trauma from injecting, or your body responding to the liquid, depending on where you inject.

Injection site reactions can be treated by:

• using an antihistamine if the site feels itchy (a tablet or cream)
• switching up your injection site each week – either use the other side of the body or make sure you use a different area of skin each time
• making sure the area is fully clean before injecting
• always using a new, unbent needle
• using an ice pack to numb the site before injecting to reduce any pain, or afterwards to reduce inflammation

Why does Mounjaro cause gallbladder issues?

According to studies, Mounjaro may cause gallbladder issues because it makes you lose weight quickly, and in turn changes the natural way that your gallbladder works (its motility).

Usually, your gallbladder works with your liver to remove cholesterol by storing bile to help to flush it out. Mounjaro makes this system work in overdrive as it slows down the digestive processes in your body. As a result, clumps of cholesterol that have not been dissolved quickly enough can crystallise into gallstones, affecting your gallbladder.

In some cases, it has been reported that patients on Mounjaro for weight loss treatment have had their gallbladders removed because of this. There is still ongoing research into whether tirzepatide (Mounjaro) is directly linked to gallstones, which can lead to gallbladder removal being needed.

It is important that you take Mounjaro as instructed by your doctor to avoid complications. This is why we always recommend regular, balanced meals and drinking plenty of water to avoid any side effects.

When taking Mounjaro, remember to:

• drink plenty of fluids – this will help your body process bile, keeping it thin
• eat regularly – small, regular meals, even with low appetite, can help your body keep things moving
• eat balanced meals – including healthy fats and fibre, helping to lower the ‘bad’ cholesterol levels

If you are thinking of taking Mounjaro and have a family or personal history of gallbladder-related issues, tell your doctor.

➤ Find out more about what to eat on Mounjaro

Will side effects get worse when I increase the dose?

It is common that side effects worsen upon titration (increasing your dose). Though this is usually temporary. Side effects like feeling sick, stomach pain, and diarrhoea usually go away after the first few days or weeks after a higher dose.

If these side effects persist and become uncomfortable, the dose you have increased to just may not be right for you, and you may need to go back down to your previous dose. Common maintenance doses available on Mounjaro are: 5, 10, and 15mg but this does not mean you cannot stay on another. Find out more about maintenance doses on Mounjaro.

However, if you experience persistent side effects that begin to affect your day-to-day life on Mounjaro even when you lower your dose, you must speak to your doctor. They may suggest an alternative weight loss treatment to Mounjaro, like Wegovy, Nevolat, or oral treatments like weight loss tablets.

Is Mounjaro safe for weight loss?

Yes, when it’s prescribed to you, and you take it correctly according to your doctor’s instructions. Mounjaro has been approved for the treatment of weight loss in the UK by the MHRA and NICE, and is safe for you to take for weight loss.

You should not take Mounjaro if you are:

• pregnant or planning to get pregnant
• under 18
• allergic to tirzepatide or other ingredients in Mounjaro
• breastfeeding

You should tell your doctor if you are thinking about taking Mounjaro if you:

• have severe problems with food digestion, such as severe gastroparesis (a disorder that slows or stops the movement of food from your stomach to your small intestine)
• have ever had pancreatitis
• have a problem with your eyes, such as diabetic retinopathy or macular oedema
• are diabetic and are using sulphonylurea or insulin
• are due to have surgery under anaesthesia

➤ Find out more information on the safety of Mounjaro

Why do I experience Mounjaro side effects after eating?

Most common side effects of Mounjaro are gastrointestinal, meaning it affects your stomach and digestion. As a result, you may get stomach pain, bloating, burping, nausea (feeling sick), vomiting, or diarrhoea after eating. This is because Mounjaro works to slow down how fast you digest food, so that you can stay fuller for longer, helping you to lose weight.

If you find yourself experiencing gastrointestinal side effects after eating on Mounjaro, try:

• eating more slowly
• avoiding greasy or fatty foods
• eating a balanced diet

You should speak to your doctor if you find that these side effects do not go away with lifestyle changes. They may suggest a lower dose or an alternative weight loss treatment.

Can Mounjaro cause gastroparesis?

The active ingredient tirzepatide, which belongs to the medication class of GLP-1 agonists, causes delayed emptying of the stomach. Although cases are very rare and there isn’t enough data on this yet, these medications may be linked to an increased risk of gastroparesis.

Gastroparesis happens when the stomach is delayed in emptying for too long and can cause stomach pain, nausea, vomiting, and feelings of fullness that don’t lessen. It’s more likely if you already have problems with digesting food or have had gastroparesis before, and your doctor isn’t likely to prescribe Mounjaro in these cases.

Is depression a side effect of Mounjaro?

Depression and mood changes have been reported as side effects by some patients taking Mounjaro. There aren’t enough cases to say whether this is directly linked to the medication, or due to other factors, such as family history or other medications taken alongside Mounjaro. Depression isn’t currently listed as a side effect in the patient information leaflet, but if you think you’ve developed depression while taking Mounjaro speak to your doctor straight away.

Can Mounjaro cause hair loss?

Mounjaro has a common side effect of hair loss. This could be caused by the medication itself, losing weight, a change in diet and lifestyle, or a mixture of all three factors. Eating a balanced, healthy diet and taking supplements may help, especially if your hair loss is caused by a nutrient deficiency since you’re eating less.

Mounjaro hair loss happens only when you’re taking the treatment and your hair should regrow if you stop taking it. Speak with your doctor if your hair seems to be thinning or you’re losing more hair than normal. They may want to check for a nutrient deficiency and can discuss your options going forward.

Does Mounjaro cause liver damage?

Mounjaro hasn’t been shown to cause liver damage, but doctors may not prescribe Mounjaro to people with severe liver problems. This is because Mounjaro contains benzyl alcohol and in people with liver problems there’s a greater chance of a condition called metabolic acidosis.

Does Mounjaro affect your eyes?

Mounjaro may affect people who have certain eye conditions, such as diabetic retinopathy or macular oedema. You should let your doctor know if you have a problem with your eyes. Mounjaro hasn’t been found to cause new eye problems as a side effect.

Can Mounjaro cause a skin rash?

Mounjaro may cause a skin rash as a common side effect, which is an allergic reaction. If you get a rash after taking Mounjaro, let your doctor know. You can take an antihistamine to see if this helps, but your doctor may want to monitor your reaction. If this happens at the injection site, it might help to try injecting into a different area.

Can Mounjaro cause body aches?

Mounjaro hasn’t been found to cause body aches, but you may feel achy because of other side effects, like being sick or having diarrhoea. If you only get body aches in a certain area, such as the stomach and back, and it doesn’t go away, speak with your doctor as this could be a sign of pancreatitis. You may get aches around your injection site, so make sure you switch this up each week.