Mounjaro side effects and how to treat them

Mounjaro, like other weight loss injections, can cause side effects. Around 1 in 10 people experience the most common ones, including vomiting, nausea, and constipation. These usually appear when first starting treatment or changing doses, as your body adjusts to the medication.

Knowing what these side effects are, how to spot them, and how to reduce your chances of getting them can make your weight loss journey smoother. It’s also important to know how to treat them if they happen, and when to seek extra support if needed. Simple steps, like eating the right foods while on Mounjaro and following your dosage schedule closely, can make a big difference.

Here, our pharmacists guide you through all the side effects of Mounjaro, explain how to avoid them where possible, and share treatments and strategies that can help you manage them more comfortably.

10 most common side effects of Mounjaro

Side Effects Frequency

Nausea
33.3%
Diarrhoea
23.0%
Constipation
17.1%
Vomiting
12.2%
Indigestion
11.3%
Acid Reflux (GERD)
8.8%
Headaches
6.8%
Hair Loss
5.7%
Sulphur Burps
5.6%
Trapped Wind
5.3%

*Between 2022 to 2024, four studies of a total 5,808 Mounjaro patients revealed the ten most common side effects experienced on the weight loss injection.

These studies were carried out over the course of 72 weeks with some patients on Mounjaro and others on placebo. Side effects, referred to as adverse effects within the studies, were tested across strengths of 5mg, 10mg and 15mg.

Mounjaro side effects questions answered by our experts

Will I get nausea on Mounjaro?

With around 1 in 3  people taking Mounjaro getting nausea, there’s a strong chance you may experience it. It usually goes away on its own quickly, as you get used to treatment, but there are also over-the-counter medications that are available to help.

Nausea on Mounjaro happens because your stomach is learning to work at a pace that is different from what it’s used to, which can lead to you feeling queasy, especially in the first few days after starting or increasing your dose.

Prescribing pharmacist Ayesha Bashir adds: “Your body often needs just one or two weeks to adjust to each dose level. Many people find these symptoms fade completely once they’re on their maintenance dose.. The key is knowing how to stay comfortable during those adjustment periods.”

How to manage nausea

Nausea management starts with timing and food choices. Many people can avoid queasiness by taking the medication with a light meal rather than on an empty stomach.

If you do find yourself struggling when increasing the dose, it’s key to keep your meals bland, as avoiding hot, spicy and rich foods can prevent discomfort while you still have a sensitive system.

Additionally, some people have found that moving the time of day they inject to evenings means that they can sleep through any mild nausea. If these solutions aren’t working for you, you can work with your prescriber who may suggest anti-nausea medication.

Why do I get diarrhoea on Mounjaro?

Diarrhoea on Mounjaro is usually caused by the medication's effects on your digestive system. This includes changing how food moves through your digestive system and how quickly your stomach empties, which can lead to an upset stomach.

Your diet on Mounjaro can also lead to diarrhoea if you’re not sticking to the right foods, like eating too many high fat meals or foods with artificial sweeteners.

More than 1 in 5 (23%) Mounjaro users report diarrhoea as an adverse effect as seen in a recent side effect study. 

It usually occurs during the first few days of starting treatment or increasing your dose as your body is still adjusting to digesting foods differently and sometimes, may overreact before finding a balance.

How to relieve diarrhoea

To relieve diarrhoea, you should:

  • Stay hydrated - drink plenty of fluids, and avoid caffeine or alcohol
  • Eat light, gentle meals - stick to bland foods. Think bananas, rice, toast
  • Medication - treatments like Imodium can put a stop to diarrhoea

How long does diarrhoea last when taking Mounjaro?

Diarrhoea usually passes within a few days, once your body gets used to treatment. If diarrhoea persists beyond 48 hours, you can get in touch with one our prescribers here or contact your GP. They can give you advice on what to do next.

Will I be constipated on Mounjaro?

Constipation happens to around 1 in 5 people who take Mounjaro.  Most people tend to experience it within the first week of starting or increasing a dose.

Weight loss injections, like Mounjaro, affect your digestion, slowing everything down – not just your stomach.

You’re also more likely to be eating and drinking less, and it’s this dehydration that when combined with the fact that food moves more slowly through your body, that causes constipation.

Less water can lead to harder and less frequent bowel movements, so it’s important you stay hydrated.

How to prevent and manage constipation

  • Eat more fibre - aim to get around 25-30g of fibre daily. High fibre foods include fruits, wholegrains, vegetables and beans and lentils
  • Stay hydrated - drink plenty of water. Warm drinks in the morning can also help to stimulate a bowel movement
  • Get active - more movement and exercise can help your bowel muscles work more efficiently. Just 20-30 minutes a day can make all the difference

If you feel that these solutions are not enough, you may wish to consider laxatives. If you still require assistance, you can always speak to our pharmacists for more advice.

Why am I vomiting on Mounjaro?

Vomiting is often brought on by intense nausea and is usually a one-off event. Some people experience it during the first few days after increasing dose, especially if they haven’t changed their eating habits.

Vomiting can be an uncomfortable, yet common side effect, with just over 1 in 10 (12.2%) people taking Mounjaro experiencing it. If you do start vomiting, it’s usually a sign to slow down and let your system reset.

Our prescribing pharmacist, Ayesha Bashir, says: “Most of the time, vomiting can be pinned down to overeating too quickly, or choosing foods that your newly slowed digestion can’t process comfortably.

If your vomiting is persistent, contact your prescriber as it could mean further investigation is needed for other causes, or a gentler dose titration is required.”

How to deal with vomiting

To help manage vomiting, sticking to clear fluids is vital. Small sips of water, flat ginger ale or electrolyte drinks work well to keep you hydrated without overstimulating your gut.

When you feel ready to eat again, it’s best to start with bland foods like dry toast or crackers before you return to regular meals.

Will I get indigestion on Mounjaro?

Indigestion affects just over 1 in 10 people (11.3%) on Mounjaro. It is a common side effect brought about by the slowing of your digestive system.

This slowing of your body's digestive system helps you feel fuller for longer. However, stomach acid also stays there longer, which can cause indigestion.

How to deal with indigestion

To prevent and manage indigestion:

  • Limit certain foods - avoid fatty, greasy and spicy foods. Try to avoid things like fizzy drinks, coffee and alcohol too. Stick to a more plain, bland diet if you’re getting symptoms
  • Sit up right after meals - sit up straight or go for a walk after meals. Lying down too quickly after eating often triggers indigestion

Take over-the-counter treatments - there are treatments available to prevent indigestion and ease it once it starts

What is acid reflux and why does it happen on Mounjaro?

Acid reflux is caused by acid from your stomach travelling back up your throat.  As Mounjaro slows down digestion, food stays in your stomach for longer, but so does stomach acid. This can make it more likely to get acid reflux, with around 1 in 10 people taking Mounjaro experiencing this side effect.

People tend to experience either acid reflux or heartburn in the early weeks of starting Mounjaro while their body is getting used to treatment.

Symptoms to look out for are a warm sensation in your chest, an acidic taste or a feeling that meals are sitting a bit heavy.

How to relieve acid reflux

To relieve acid reflux you should:

  • Eat smaller portions - stick to small regular meals throughout the day
  • Choose bland foods - avoid fatty, greasy foods and things like alcohol and coffee. Stick to a bland diet of things bread, toast, rice and plain white meats
  • Try over-the-counter or prescription treatments – over-the-counter treatments like Gaviscon can relieve acid reflux quickly. Medications like omeprazole and esomeprazole offer longer-term control if needed. Your pharmacist can help by giving you the best options available

Carrying less weight around your middle means less pressure on your stomach, so while Mounjaro might temporarily worsen reflux, the weight loss it enables often resolves reflux issues you might have had for years.

Will I get headaches on Mounjaro?

You might get headaches on Mounjaro, but it’s much less likely with only 1 in 20 people reporting headaches. They tend to come on due to dehydration or not eating enough.

These headaches typically appear in the first few weeks of treatment or after dose increases and fade as the body finds its rhythm.

You might also experience headaches as your blood sugar levels reach their new normal, particularly if you eat much less.

Dealing with headaches

For headaches, staying hydrated is important. Aim for at least 2 litres daily. You can also try over-the-counter treatments like paracetamol for relief.

Should I worry about hair loss on Mounjaro?

Headlines about hair loss on Mounjaro can be concerning, but it’s important to know that this is typically related to rapid weight loss, rather than just the medication itself. It’s often a temporary side effect. Additionally, with less than 1 in 10 (5.7%) experiencing it, it’s not very common.

When you lose weight quickly, your body can shift hair follicles into a 'resting phase', leading to increased shedding a few months into treatment. This same effect happens with any significant weight loss, whether through medication, diet, or surgery.

Will my hair grow back on Mounjaro?

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. 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.”

Why am I having sulphur burps on Mounjaro?

Sulphur burps happen on Mounjaro because of:

Your stomach emptying slower -Mounjaro delays how quickly food leaves your stomach, which can mean it sits there longer and has more time to ferment, creating that ‘sulphur’ smell

Changes in gut bacteria - slowed digestion can alter the balance of gases produced by your gut microbes.

Protein breakdown - when food (especially protein-rich foods like eggs, meat, or dairy) lingers in the stomach/intestines, bacteria can break down sulphur-containing amino acids, producing hydrogen sulphide gas (the “rotten egg” smell)

Less than 1 in 10 people experience sulphur burps on Mounjaro (5.6%), and they're usually temporary and manageable, often settling within 2-4 weeks as your body adjusts.

How to manage sulphur burps

To manage sulphur burps:

  • Avoiding sulphur-rich foods (like eggs, broccoli, and red meat) and fizzy drinks; eating smaller meals throughout the day and staying well-hydrated can help significantly.
  • Eat smaller lighter meals and stay hydrated
  • Avoid drinking fizzy drinks
  • Avoid lying down 2-3 hours after eating food (don’t eat before bed!)

Why do I get trapped wind with Mounjaro?

As Mounjaro slows digestion, gas can become trapped more easily in your intestines, causing 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 might be recognised by those sharp, sometimes severe abdominal pains, and can be alarming when you first experience them.

How do I manage trapped wind?

Movement is your best friend when dealing with trapped wind—even gentle stretching or a short walk can provide quick relief.

Beyond that, focus on how you eat rather than just what you eat: chew thoroughly, avoid straws and chewing gum (which increase air intake), and consider temporary limits on gas-producing foods.

Alternatively, you can alleviate symptoms of trapped wind by taking over-the-counter medications like simeticone.

Other highly searched Mounjaro side effects

With the top 10 most common side effects covered, we thought it important to look at side effects that are less common. Below are side effects that affect less than 1 in 20 (<5%) that are highly searched for.

Side Effect Frequency

Nausea
33.3%
Diarrhoea
23.0%
Constipation
17.1%
• • •
Gallbladder disease
1.7%
Hypoglycaemia
1.6%
Gallstones
1.4%
Pancreatitis
0.2%

Body aches on weight loss injections

Body aches typically happen for several reasons:

  • Your body is losing water quickly as it adjusts
  • Changes in essential minerals like salt and potassium
  • Your body's natural reaction to significant changes in how it processes food and energy

Some people also find that digestive discomfort can appear as aching in their back or stomach muscles.

How to ease body aches

To manage and deal with body aches caused by Mounjaro, we recommend:

  • 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 can help get rid of aches or even using an ice pack. Find what works best for your body

Bloating when on Mounjaro

Bloating is most likely to occur in the first few weeks, and may come back when you change dose. This usually happens during your first 2-4 weeks of treatment and after making a change.

Bloating happens because Mounjaro changes how quickly food moves through your system, creating that lasting feeling of fullness that drives successful weight loss.

Some people worry that higher doses mean worse bloating, but that's not always true - many people find their digestion stabilises once they're established on their optimal dose.

How to manage bloating

Managing bloating involves simple lifestyle adjustments that quickly become routine. Mindful eating makes a real difference - taking your time with meals, avoiding carbonated drinks, and being selective about foods that cause gas.

Should bloating persist beyond the adjustment period, you can always work with your prescriber on a more gradual dosing schedule.

Does Mounjaro cause a sore throat and mouth ulcers?

Sore throat and mouth ulcers are uncommon side effects that some people experience with Mounjaro, often linked to dry mouth or the body's adjustment to rapid weight loss.

These symptoms are typically mild and temporary, with mouth ulcers healing within a week and sore throats coming and going during early treatment.

Relief is simple: rinse with warm salt water several times daily, stay hydrated with regular sips, and use sugar-free lozenges to soothe your throat.

For mouth ulcers, your pharmacist can recommend protective gels that reduce pain while eating. Avoiding acidic or spicy foods during flare-ups helps prevent further irritation.

Why am I feeling cold and tired on Mounjaro?

Feeling more cold than usual and reaching for extra jumpers is a common experience during the early weeks of Mounjaro treatment.

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.

Fatigue typically peaks during the first 2-3 weeks of treatment or after dose increases, then gradually improves as your body becomes more efficient at using stored energy.

Many people report improved energy levels once they've adjusted, especially as weight loss reduces the physical strain on their bodies. The cold sensitivity may persist longer, particularly as you lose insulating body fat, but this is a sign that the medication works effectively.

How to manage

Ensure your diet contains enough vital nutrients, such as protein, healthy fats, and carbohydrates. B vitamins and iron supplements can help if fatigue persists, though check with your pharmacist first.

Hot baths, cosy socks, and keeping active can all help with temperature regulation. Most people find that as their bodies adjust and they develop new routines, these symptoms become much less noticeable.

Mounjaro eye side effects

The most frequently reported issue is temporary blurred vision, which typically occurs during the first few weeks of treatment or after dose increases. This happens because Mounjaro can cause rapid improvements in blood sugar levels. When your blood sugar drops quickly, the fluid levels in your eyes can shift which affects how your eyes work.

For most people, this blurriness resolves within 2-4 weeks as blood sugar levels stabilise. Some users also report mild eye dryness or discomfort, particularly if they're already prone to dry eyes.

If you notice blurred vision, don't panic – it's usually temporary and manageable. Stay well-hydrated (aim for 8 glasses of water daily) as dehydration can worsen eye symptoms. Using preservative-free artificial tears can help with any dryness or discomfort.

Any sudden vision loss, severe eye pain, or vision changes lasting more than a month should be reported to your prescriber immediately. While rare, these need prompt assessment. For most people, any minor vision changes resolve completely once their body adjusts to the medication.

Can I get insomnia when taking Mounjaro?

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 disruption can occur 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.

Ways to reduce the chance of insomnia include taking your injection in the morning rather than evening, avoiding caffeine after 2 p.m., and establishing a calming bedtime routine. Light exercise during the day (but not close to bedtime) can also improve sleep quality.

If sleep problems persist beyond a few weeks, speak with your healthcare provider about adjusting your dose schedule or trying short-term sleep support.

Gallbladder issues and gallstones

Gallbladder problems, including gallstones, are rare side effects that can occur with any rapid weight loss , including when using Mounjaro. 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.

The symptoms of gallbladder problems 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).

The pain often comes in waves or 'attacks' lasting from minutes to hours, ranging from mild discomfort to severe pain. Some people also notice clay-coloured stools or dark urine.

These symptoms require medical evaluation to determine if gallstones or other gallbladder issues are present. It's worth noting that many people have gallstones without knowing it, and rapid weight loss can sometimes reveal pre-existing stones rather than cause new ones.

Pancreatitis

Pancreatitis is a very rare but serious side effect that affects fewer than 1 in 1,000 people taking Mounjaro. Your pancreas, which sits behind your stomach, can become inflamed, though it's important to understand that most people never experience this. If you have ever had pancreatitis before, you should not take this treatment.

Clinical trials and real-world data from millions of users show that serious side effects like pancreatitis are extremely uncommon. Your prescriber has determined that the benefits of treatment far outweigh these small risks.

The symptoms of pancreatitis are distinctive and include severe stomach pain that may spread to your back, nausea and vomiting that doesn't improve, fever, and a tender abdomen. The pain is typically constant and severe, quite different from the mild stomach discomfort some people experience when adjusting to Mounjaro.

Head of Pharmacy Jason Murphy adds: “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.”

Quick medical attention is important; healthcare providers can easily check for pancreatitis with blood tests.

Can Mounjaro cause cancer?

There is little to no evidence that Mounjaro causes cancer. In fact, the risk of certain cancers could be reduced. By taking control of your weight and metabolic health with Mounjaro, you're more likely to reduce your risk of many serious health conditions, including certain types of cancer linked to obesity. For more information, read our guide on the other benefits of Mounjaro.

However, the manufacturer has stated that you should not use Mounjaro if you or a family member has ever had a type of thyroid cancer called medullary thyroid carcinoma or if you suffer from multiple endocrine neoplasia (MEN2).

You should contact your healthcare provider if you ever experience any unusual symptoms, e.g., a lump in the neck.

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Jason Murphy - Head of Pharmacy
Jason Murphy , Head of Pharmacy on 21 August 2025
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