The ultimate guide to Mounjaro side effects

Wednesday, January 8, 2025

Mounjaro (tirzepatide) is a highly effective weight loss injection that has helped countless people lose weight. However, like any medication, Mounjaro comes with potential side effects. For some, these can feel unpleasant enough to stop treatment altogether.

The good news is that many side effects of Mounjaro are only temporary. They often get better within the first days and weeks as your body gets used to the medication, and there are helpful ways to manage these side effects.

So, if you’re experiencing unpleasant effects after starting Mounjaro or moving up a strength, don’t give up. We will tell you more about what causes them and how you can manage them.

In this guide, we explain the most common side effects of Mounjaro, share tips to manage each of them, and help you understand when to get medical advice for more serious concerns.

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What are the side effects of Mounjaro?

Mounjaro side effects vary because everyone’s body handles medicine differently. Many people don’t get any side effects at all. But it’s best to be prepared. Knowing what’s normal can make it easier to stick with the weight loss treatment and know when to get more help.

Side effects for Mounjaro are broadly categorised based on how often people experience them:

Very common side effects: These happen for more than 1 in 10 people and include digestive (tummy) symptoms like nausea, diarrhoea, vomiting, and constipation (1).
Common side effects: These affect between 1 in 10 and 1 in 100 people and include heartburn, burping, bloating, headaches, dizziness, and fatigue (tiredness).
Rare side effects: These occur in fewer than 1 in 100 people and include injection site reactions, gallbladder issues, inflamed pancreas, and high levels of pancreatic enzymes.

Most side effects are temporary, often appearing during the first few days or weeks of treatment or after increasing your dosage. Once your body adapts, these symptoms lessen and can disappear. In the meantime, small changes to your routine can make any side effects more manageable.

How to manage very common side effects of Mounjaro

Mounjaro nausea

Nausea affects around 2 in every 10 people who use Mounjaro, so feeling sick on Mounjaro is pretty common (2). Why does Mounjaro cause nausea? Because it causes food to stay in your stomach longer (3). This can leave you feeling full and uncomfortable, especially after eating too much or too quickly.

Tips for Mounjaro nausea relief:

Eat foods like crackers, toast, and plain rice that are gentle on your stomach.
Avoid spicy, greasy, or heavily processed foods, which can worsen nausea.
Stay hydrated by sipping water or herbal teas to help settle your stomach.
Drink ginger tea or ginger lozenges, which may naturally ease nausea.
If nausea persists, we may recommend an anti-nausea medication.

Mounjaro diarrhoea

Diarrhoea is the second most common adverse effect of Mounjaro injections, occurring in 1-2 of every 10 users (2). As Mounjaro changes how your stomach and intestines handle digestion, your stools can soften and become loose.

Tips to manage Mounjaro diarrhoea:

Drink plenty of water or electrolyte fluids to avoid dehydration.
Eat foods that are easy to digest, such as bananas, rice, and plain toast.
Avoid caffeine and alcohol, which have natural laxative effects.
Take an anti-diarrhoeal medication like loperamide.
Gradually introduce foods back into your diet to avoid once diarrhoea has improved.
If you have no improvement or have severe diarrhoea, speak to us or your prescriber.

Mounjaro vomiting

Another of the most common Mounjaro side effects is vomiting. Like nausea, vomiting on Mounjaro is linked to slowed stomach emptying. It can also be triggered by the feelings of nausea, so both can be treated in similar ways.

Tips to manage Mounjaro vomiting:

Eat smaller meals to stop your stomach feeling overwhelmed.
Avoid eating spicy, processed, or oily foods, which can worsen nausea and vomiting.
Try anti-nausea home remedies, like drinking ginger or peppermint tea.
Drink plenty of fluids to stay hydrated.
Take your Mounjaro dose with food to help settle your stomach.
Speak to us or your prescribing doctor if vomiting prevents you from keeping fluids or food down.

Mounjaro constipation

While diarrhoea is more common, some people taking Mounjaro might experience the opposite problem: constipation. This happens because the drug slows digestion, meaning food stays in your system longer, giving more time for stools to harden.

Along with reduced appetite, people using Mounjaro often feel less thirsty during the day. As they drink less, they also increase their chance of getting constipated with Mounjaro.

Tips to manage Mounjaro constipation:

Add high-fibre foods like whole grains, fruits, and vegetables into your diet.
Drink plenty of water, which helps keep things moving through your digestive system.
Stay active—even light activity stimulates digestion and improves constipation (4).
Take over-the-counter laxatives to help soften your stools.
Talk to a doctor if you’re having ongoing bowel issues.

How to manage common side effects of Mounjaro

Mounjaro headache

Headaches can occur while taking Mounjaro as the drug lowers blood glucose levels (5). These rapid changes can cause a temporary dip in blood sugar levels, which is known to trigger headaches. Dehydration may also contribute to headaches, with many people on Mounjaro eating and drinking less than usual.

Tips to manage Mounjaro headache:

Drink plenty of water regularly throughout the day to prevent dehydration.
Avoid skipping meals and include balanced snacks to maintain steady blood sugar levels.
Use over-the-counter pain relief medications like paracetamol or ibuprofen.

Mounjaro fatigue

Tiredness and fatigue are other common side effects of Mounjaro injections. The drug’s role in lowering blood sugar can initially leave you feeling a little drained. Additionally, slower gastric emptying may temporarily disrupt energy levels due to delayed nutrient absorption.

Mounjaro tiredness can also happen when a person isn’t eating as much as usual, and even more so if they are eating in a calorie deficit. So it’s not just the medicine, it’s actively losing weight that can affect our energy.

Tips to manage Mounjaro fatigue:

Aim for around 8 hours of quality rest each night to support recovery.
Eat balanced meals that include protein, healthy fats, and complex carbohydrates.
Take multivitamins to ensure you get all the nutrients you need.
Stay active. (If you’re exhausted, try light activity, like walking or yoga.)
Limit alcohol and caffeine, which can disrupt your sleep.

If you still feel tired a few weeks after starting Mounjaro injections or increasing your dose, speak to us or your doctor. Your fatigue might be caused by deficiencies and can be managed with supplements.

Mounjaro dizziness

Dizziness is another potential side effect of Mounjaro and is one of the signs of low blood sugar. Alternatively, your dizziness while taking Mounjaro might be caused by dehydration. Either way, once your body gets used to the drug, you should stop feeling dizzy, or lightheaded.

Tips to manage Mounjaro dizziness:

Eat small snacks when you feel dizzy to help stabilise blood sugar.
Drink plenty of water to stay hydrated throughout the day.
Stand up slowly from sitting or lying down to avoid sudden drops in blood pressure.
Maintain a regular eating schedule to keep blood sugar steady.
Blood sugar monitoring can help you understand your glucose levels better.

Mounjaro heartburn

Heartburn is caused by acid reflux, where stomach acid flows back into the oesophagus. Mounjaro’s effect on slowing gastric emptying means food remains in the stomach longer, which can lead to increased acid production. This can aggravate reflux, especially if you’re already prone to heartburn.

Tips to manage Mounjaro heartburn:

Eating smaller, more frequent meals to reduce pressure on your stomach.
Reducing your intake of spicy, acidic, or fatty foods that can worsen reflux.
Stay upright for 2 hours after eating to prevent acid from rising up your oesophagus.
Over-the-counter remedies like Gaviscon or Rennie can neutralise stomach acid.
Consider a short course of acid reflux medications (like Omeprazole and Lansoprazole) to reduce acid production for more severe cases.

If you want more information, we have an entire article about Moujaro injections and heartburn, where you can learn how to relieve this uncomfortable side effect.

Mounjaro sulphur burps

Some people on Mounjaro injections experience sulphur burps or egg burps. Mounjaro burping is caused by delayed gastric emptying. The longer food stays in the stomach, the greater the opportunity for fermentation by gut bacteria, producing gas with a distinct sulphur-like smell.

Tips for managing Mounjaro sulphur burps:

Cut back on foods high in sulphur, such as onions and garlic (our patients also tell us red meat is a real trigger).
Eat smaller, more frequent meals to reduce the gas produced during digestion.
Chew food thoroughly and eat slowly to stop you from swallowing so much air.
Take antiflatulent medications like simethicone to ease discomfort (6).

Mounjaro bloating

Rather than escaping up through your throat as a belch (burp), excess gas can accumulate in the stomach or intestines and cause bloating. Bloating can also be related to constipation or caused by the slower movement of food and liquid through your digestive tract.

Tips for managing Mounjaro bloating:

Chew food thoroughly to aid digestion and ease pressure on your stomach.
Eat slowly to reduce swallowed air, which can contribute to bloating.
Avoid fizzy drinks, as these introduce extra air into your stomach.
Exercise regularly to help gas pass through your digestive system and ease bloating (7).

Are there any serious Mounjaro side effects?

Clinical trials have shown that Mounjaro weight loss injections are generally safe and effective when used as prescribed, with most side effects being mild and temporary. For most people, the benefits of improved blood sugar control and weight management far outweigh the risks.

However, although extremely rare, serious side effects can occur and include:

Severe allergic reactions

Allergies to Mounjaro weight loss injections are rare, with only a few reported cases of reactions at the injection site (8)(9). You can easily treat these mild reactions using antihistamines to ease itching, and they tend to settle as your body adjusts to the drug.

While mild allergies are nothing to worry about, there have been a handful of cases of severe, life-threatening anaphylaxis in response to the drug (10). Anaphylaxis is a medical emergency that needs immediate treatment. Look out for symptoms like swelling, rash, or difficulty breathing. Call 999 if these occur.

Acute pancreatitis

Pancreatitis is another very rare side effect of Mounjaro, affecting less than 1 in every 100 people using Mounjaro (1). In fact, it’s so uncommon that some studies have concluded there is no increased risk of pancreatitis while on tirzepatide (11). The risk may be slightly higher if you have had pancreatitis before.

Acute pancreatitis is a serious condition with symptoms such as severe abdominal pain, nausea, and vomiting. It typically requires hospital treatment, and while most patients usually feel better within a few days, there is a chance of life-threatening complications (12). Your doctor may recommend that you stop taking Mounjaro during recovery.

Gallbladder problems

Mounjaro can increase the risk of gallbladder issues, such as gallstones (cholelithiasis) or inflammation (cholecystitis) (1). These side effects are rare and more likely if you are taking higher doses of tirzepatide, using the drug long-term, or are taking Mounjaro for weight loss (13).

The exact mechanism isn’t fully understood, but it may be related to GLP-1 inhibitors like Mounjaro reducing the hormone cholecystokinin, which is essential for healthy gallbladder function (14). Rapid weight loss may also increase the risk of gallbladder problems. Seek immediate medical attention if you suspect gallbladder complications, as untreated cases can lead to more serious issues.

General advice on Mounjaro side effects

Most side effects of Mounjaro are mild and tend to subside within a few weeks of starting treatment or increasing your dose as your body adjusts to the medication. Try to be patient.

While you wait, there are plenty of ways to make you more comfortable, including things like:

Stay hydrated by drinking plenty of water.
Eat smaller, more frequent meals to prevent nausea and vomiting.
Avoid spicy, greasy, or processed foods.
Limit your alcohol and caffeine intake.
Stay active (plus, exercise will help get you closer to your weight loss goals)
Prioritise a balanced, nutrient-rich diet.
Use OTC remedies like stool softeners, antacids, or anti-nausea drugs as needed.

If side effects persist despite these changes, get worse over time, or seem unusual, reach out us or your Mounjaro provider. We will assess your symptoms, possibly adjust your dosage, or help you determine if another weight loss medication might be a better fit.

Weight loss medications that work for YOU

At Oxford Online Pharmacy, we offer an online doctor service for anyone interested in buying Mounjaro or another weight loss medication. Our experienced team considers your medical history, goals, and unique needs to recommend the best treatment plan that delivers excellent results while minimising side effects.

With the proper support, you can stay on track toward achieving your health and weight loss goals. Contact our team today or start your online consultation for Mounjaro UK here.

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