Around 1 in 10 people get the most common Mounjaro side effects, like nausea, vomiting, or constipation. These usually happen when you first start treatment or increase your dose, as your body gets used to the medication. The good news? They’re typically mild and can often be managed easily at home.
In this guide, our clinicians explain the side effects of Mounjaro, how to recognise them, and what you can do to lower your chances of getting them. We’ll also share simple ways to relieve symptoms at home and let you know when it’s time to speak to your doctor.
Three Key Takeaways
The most common side effects of Mounjaro are nausea, diarrhoea, constipation, and vomiting. These are usually mild and often go away on their own.
Most side effects can be managed safely at home with small diet or lifestyle changes, or with over-the-counter remedies.
If your side effects are hard to cope with, or you’re worried about them, speak to your prescriber.
What are the most common Mounjaro side effects?
The very common Mounjaro side effects (affecting more than 1 in 10 people) are:
nausea
diarrhoea
constipation
vomiting
stomach pain
While very common, not everyone will get these and how long they last will vary from person to person.
Managing very common Mounjaro side effects
You can reduce and manage most common Mounjaro side effects by making small lifestyle and dietary changes. Plus, over the counter treatments like antacids can help too.
Nausea (feeling sick)
To deal with nausea we recommend:
eating smaller meals more frequently
stopping eating the moment you start to feel full
sticking to bland foods like rice, bread, or crackers
drinking hot herbal teas, like ginger or peppermint
taking small, regular sips of cold water
avoiding fatty and processed foods
taking your mind off it – watch some TV, listen to some music
getting some fresh air – take a walk, if you can, or sit outside
Nausea is usually only temporary and should ease soon. To prevent it, make sure you’re well hydrated, and sticking to small, regular meals.
If nausea lasts for more than a couple of days, speak to your doctor.
Diarrhoea
If you’re getting diarrhoea we recommend:
Staying hydrated. Diarrhoea can lead to dehydration, which can make you sick and make other side effects worse.
Taking rehydration sachets. These over-the-counter sachets make sure you stay hydrated and keep your electrolytes topped up.
Eat foods that are easy to digest. Think bananas, plain toast, or rice.
Avoid natural laxatives, like caffeine and alcohol. These not only dehydrate you but can make diarrhoea worse.
If you have diarrhoea and it doesn’t go away after 7 days or if you notice any blood in your stool, you need to get medical advice from a doctor.
Constipation
If you’re dealing with constipation, you should:
Update your diet plan
A balanced, healthy diet can help relieve constipation.
Eat more fruits and vegetables, like apples, raspberries, raisins, broccoli, or carrots. These are high in fibre and can help loosen stools.
Eat more whole grains, like oats or brown rice.
Most adults should get 30 grams of fibre a day, but not many people do. If you’re not getting that, increase your intake gradually. Adding too much fibre to your diet too quickly can cause diarrhoea.
Change your toilet habits
Try going to the toilet at a regular time, every morning, for example.
Don’t rush on the toilet. Give yourself time to go, but don’t force it.
Don’t try to hold it. Go to the bathroom as soon as you feel the need.
Try a better toilet posture. Some people find resting their feet on a stool makes it easier to go.
Do a stomach massage. Massaging your stomach on the toilet can help you go.
Get more exercise
Regular exercise helps with constipation. If you’re not up for a run, try taking a daily walk to get your digestive system moving. Going for a walk after eating meals can also help with digestion.
Stay hydrated
Drinking plenty of water can help loosen stool and prevent constipation.
Drinking water keeps your stool soft and hydrated making it easier for it to pass through your digestive system.
Water helps fibre work properly. If you’re eating enough fibre, you need to up your water intake to get the most out of it.
Try an over-the-counter laxative
There are plenty of laxatives that can help with constipation, but it’s important to speak to your prescriber first.
Rashes and injection site reactions
It’s not unusual to see rashes, bruising, orswelling at your chosen injection site. You might also notice some pain and itching. This usually settles as you get used to taking the injections, but it’s worth keeping an eye on if it gets worse or doesn’t go away. If you’re dealing with issues at your injection site, try:
Regularly rotating where you do your injection. Avoiding the same spot gives your skin time to heal.
Using antihistamine cream. Injection site rashes might be caused by a mild allergy, and an antihistamine can help reduce it.
Making sure your injection site is always clean. Clean any area you’re going to inject thoroughly before starting.
Numbing the area before injecting. This can prevent irritation and pain.
Common Mounjaro side effects
The common Mounjaro side effects (affecting 1 in 10 people) are:
itching, eczema, or a rash
acid reflux (heart burn)
dizziness
indigestion
bloating
burping
wind
injection site reactions (redness or itching)
low blood pressure
hair loss
low blood sugar
feeling tired (fatigue)
increased levels of lipase (a pancreatic enzyme) in the blood
increased levels of calcitonin (a thyroid hormone that regulates your calcium levels) in the blood
These side effects also tend to go away on their own or when you stop treatment.
Some common side effects can be made worse, or more likely to occur, by other medicines you’re taking. That’s why it’s important to tell your clinician about any medications you’re on before starting Mounjaro.
For example, certain treatments for type 2 diabetes, like metformin, can increase your risk of low blood sugar when combined with Mounjaro.
If you begin any new medication while taking Mounjaro, let your prescriber know so they can check it’s still safe and suitable for you.
“Worrying about side effects is totally natural, especially when you’re starting a new medication. Try to remember that most side effects are mild and serious side effects are very rare. By knowing what the side effects can be, you put yourself in the best position to deal with them at home or to know when to speak to a healthcare professional for advice. In most cases, side effects go away on their own as your body gets used to the medication, so you shouldn’t have to worry too much.”
Getting side effects on Mounjaro isn’t unusual and over 1 in 10 people will get them. However, some are more common than others.
“To avoid the most common Mounjaro side effects we always recommend:
Staying hydrated. Getting enough water each day is key to avoiding constipation and headaches. It’s also important to stay hydrated if you’re getting diarrhoea.
Eating a balanced diet containing plenty of fibre, whole foods, and protein. These foods keep you full and prevent side effects.
Avoid spicy foods, fatty foods, alcohol and caffeine. These foods can be hard on your stomach, leading to side effects. Alcohol and caffeine can make side effects worse and cause dehydration.
Move more! Regular exercise reduces side effects and increases weight loss; it’s win-win. Small changes, like the taking the stairs or a daily walk can make a world of difference.”
While most side effects are manageable and mild, there are some rarer side effects that can be more serious. These side effects only happen to less than 1% of people who take Mounjaro, but it’s important to know and understand them so you know what to do if they happen to you.
The uncommon side effects of Mounjaro include, but are not limited to:
inflamed pancreas (pancreatitis)
rapid pulse
increased levels of amylase (pancreatic enzyme)
low blood sugar
injection site pain
gall bladder infection (cholecystitis)
If you get symptoms of these side effects, stop taking Mounjaro and get immediate medical help. Either by calling 999 or going to the hospital.
It’s important to remember that serious side effects with Mounjaro are very rare, affecting fewer than 1% of people. While they can sound worrying, they’re unlikely to happen. Most people only experience mild side effects as their body adjusts to treatment.
All medicines can cause serious side effects, even everyday ones like paracetamol. But the health benefits of weight loss usually far outweigh the risks.
Before prescribing, our clinicians always make sure treatment is safe and suitable for you. And if you’re ever worried about side effects, we’re here to talk and help.
While very rare, it’s still important to understand these side effects and know what to look out for, so you can manage them safely.
Gall bladder issues
Gall bladder issues, like gallstones or inflammation can happen, and while rare, it’s a serious side effect that can happen. This is because Mounjaro reduces the amount of a hormone you make called cholecystokinin, which helps your gall bladder function healthily.
Losing a lot of weight very quickly can also cause problems with yourgallbladder. When you lose weight quickly, your liver releases extra cholesterol into bile, which can form stones in your gallbladder. Whilst this affects fewer than 1 in 100 people taking Mounjaro, it's worth being aware of the symptoms.
These symptoms include pain in the upper right side of your abdomen or between your shoulder blades, particularly after eating fatty foods. You might also experience nausea, vomiting, fever, or notice yellowing of your skin or eyes (jaundice).
If you experience anything like this, stop taking Mounjaro, and speak to a doctor as soon as possible.
Low blood sugar (hypoglycaemia)
If you also have type 2 diabetes, and you’re taking medications to lower your blood sugar alongside Mounjaro, low blood sugar can be more likely. This can cause symptoms like:
dizziness
fatigue
hunger
weakness
confusion
irritability
faster heartbeat
sweating
anxiety
If you get these symptons, eat or drink something that contains sugar. Think fruit juice, fizzy drinks (not diet!), sweets, or glucose/dextrose tablets. If this improves your symptoms, eat a longer-acting carbohydrate, like biscuits, bread or anything similar.
You should talk to your doctor if this happens regularly.
IMPORTANT: Very low blood sugar can lead to a loss of consciousness. If this happens to you or someone you’re with, get emergency medical attention.
Allergic reactions
As with all medications, there is also a possibility of experiencing an allergic reaction to Mounjaro. This is considered a very rare side effect, affecting fewer than 1% of people who take it.
If you notice symptoms of a severe allergic reaction, like difficulty breathing, swelling of the lips or tongue or feeling like you’re going to collapse, get emergency medical attention.
Inflammation of the pancreas (pancreatitis)
While pancreatitis is uncommon, it is a serious side effect of Mounjaro. It usually causes severe pain in the stomach or back that doesn’t go away with time or changing position. It’s often accompanied by a high temperature or being sick. If you get these symptoms, you need to stop using Mounjaro and get immediate medical attention.
Mounjaro can cause stomach aches, and other side effects which may seem similar to what we’ve described here. The pain from pancreatitis is extreme, and it doesn’t go away. You’ll know the difference if it happens.
“In my experience, patients sometimes worry unnecessarily about every stomach twinge, but true pancreatitis pain is unmistakable. If you experience severe, persistent abdominal pain that doesn't improve with rest or position changes, especially if accompanied by vomiting or fever, that's when you need immediate medical attention.”
The only studies claiming it causes thyroid cancer, were conducted on a group of male and female rats. Rats are significantly more likely to develop cancer than humans, and this trial does not necessary mean there’s any increased risk of cancer from taking Mounjaro.
One study investigating the active ingredient in Mounjaro (tirzepatitide) and cancer rates, actually found that Mounjaro has been linked to reducing some cancers, especially those linked to obesity.
Are there long-term side effects from taking Mounjaro?
The longest clinical trial of Mounjaro (72 weeks) did not report finding any long-term side effects in the participants.
However, some of the side effects of Mounjaro, if left untreated, can lead to more long-term issues. These include:
Pancreas damage from untreated pancreatitis: If left untreated, pancreatitis can lead to permanent damage. There are also studies that have found around 25% of people who get acute pancreatitis may get it again.
Kidney damage from severe dehydration: If you get severe vomiting or diarrhoea and it’s not treated, it can impact your kidney health. In very rare and severe cases this can lead to kidney failure.
Important: These long-term side effects are not caused by Mounjaro directly, but from not treating rare side effects caused by the medication.
Remember: Mounjaro is a new medication, so there’s limited information about its long-term side effects. However, serious long-term issues are extremely rare, and Mounjaro is considered safe for long-term use.
Your prescriber will always review your health before prescribing Mounjaro long-term. If there are ever any concerns about side effects, they’ll stop treatment and discuss alternative options with you.
Are Mounjaro side effects worse than Wegovy?
Mounjaro side effects aren’t usually worse than those with Wegovy. Both medications have very similar side effects, some are just more common depending on which one you’re taking.
For example, with Wegovy, headaches and fatigue are lot more common, but with Mounjaro it’s more likely to get skin reactions like eczema and rashes or low blood pressure.
It’s also important to understand that medications affect everyone differently. Some people may react more to Mounjaro than Wegovy or the other way around. Our clinicians will work with you to find the treatment that works best, while minimizing any side effects.
Frequently asked questions by our patients about other Mounjaro side effects:
When do Mounjaro side effects start?
Mounjaro side effects can start quickly after taking the medication. Most start within a few days but go away just as quickly. They might also come back or start when you increase dose, as your body needs to get used to more medication.
How long do Mounjaro side effects last?
Most Mounjaro side effects tend to go away on their own within a couple of days or weeks. If they don’t get better or get worse and start preventing you from going about your day-to-day life, you should speak to your prescriber.
Will I get headaches on Mounjaro?
You might get headaches on Mounjaro, but it’s much less likely as only 1 in 20 people report headaches. They tend to come on due to dehydration or not eating enough.
Headaches typically appear in the first few weeks of treatment or after dose increases and fade as the body finds its rhythm.
Does Mounjaro cause hair loss?
Yes. Mounjaro causes hair loss in around 5% of people who take it. The good news is that it’s not usually permanent and stops within your first few months of treatment. In most cases, any hair loss is related to rapid weight loss, rather than just the medication itself.
Ian Budd, a clinical prescriber, adds: “Hair shedding usually begins around 3-6 months into treatment and isn't necessarily linked to specific doses, but has been recognised at higher doses.
The reassuring news is that this is temporary; most people notice regrowth starting 3-6 months after the shedding begins, as their weight stabilises and their body adjusts. We advise anyone experiencing this to help themselves by using treatments like Regaine or taking finasteride, though it’s important to note that only men can take finasteride.
Remember, if you're experiencing hair loss, it often signals positive changes in your body - it just needs time to adjust to your new, healthier weight.”
Sulphur burps happen on Mounjaro because of your stomach emptying slower, changes in gut bacteria and proteins breaking down, whichproduces more hydrogen sulphide gas, causing burps with a “rotten egg” smell.
Our clinicians can help you understand and manage sulphur burps.
Why do I get trapped wind with Mounjaro?
You get trapped wind on Mounjaro because as it slows digestion, gas can become trapped more easily in your intestines. This can cause discomfort that ranges from mild to quite intense. The good news is that this typically peaks during early dose transitions and improves as your body adjusts.
Trapped wind can be recognised by those sharp, sometimes severe abdominal pains, and can be alarming when you first experience them.
Why am I feeling cold and tired on Mounjaro?
You might notice you’re more sensitive to temperature or feeling slightly drained, as your body adjusts to taking in fewer calories and working hard to burn stored fat.
While fatigue typically peaks during the first 2-3 weeks of treatment, or after dose increases, it gradually improves as your body becomes more efficient at using stored energy. Cold sensitivity may persist longer, particularly as you lose insulating body fat, but this is a sign that your treatment is working well.
Can I get insomnia when taking Mounjaro?
You can get insomnia while taking Mounjaro, but it’s quite rare. Insomnia is a very uncommon side effect of GLP-1 treatments, including Mounjaro, particularly during the first few weeks of treatment or after dose increases.
Sleep disruptions can happen due to changes in your metabolism, mild nausea, or simply your body adjusting to eating less. Most people find that their sleep patterns return to normal once their body settles into the medication.
How do you deal with bloating on Mounjaro?
To deal with bloating:
take your time with meals
avoid carbonated drinks
be selective about foods that might cause gas
If you keep getting bloating, even after your adjustment period, you can always work with your prescriber on a more gradual dosing schedule.
Why do I get body aches on Mounjaro and how do I manage them?
Body aches typically happen for several reasons:
your body is losing water quickly as it adjusts
changes in essential minerals like sodium and potassium
your body's natural reaction to significant changes in how it processes food and energy
You can ease body aches by:
Looking after your muscles and joints - stay hydrated and try to maintain plenty of gentle movement.
Making sure you’re getting the right nutrition - include plenty of protein in your diet (fish, chicken) and make sure you’re eating leafy greens, bananas, nuts and seeds. These provide you with magnesium and potassium, which help stop muscle cramps and aches.
Trying hot and cold therapy – a hot bath or shower, or even using an icepack, can help get rid of aches. Find what works best for your body.
Chemist 4 U uses cookies (and other techniques) to enhance your shopping experience.
Read more about our cookie policy, terms and conditions and privacy statement. By continuing on this site and accepting our cookies you agree to the collection of information on this basis by us and by third parties on the platform as well as direct email marketing. Please customise your cookie settings below.
Find out more about our data policies.
