What are the most common side effects of Mounjaro?

The most common side effects of Mounjaro (tirzepatide) are gastrointestinal and include nausea, vomiting, diarrhoea, constipation, and abdominal pain. These typically occur when starting treatment or increasing the dose, and usually improve over time. Eating smaller meals and avoiding fatty foods can help reduce nausea.

Does Mounjaro cause hair loss?

Some people experience temporary hair loss (telogen effluvium) while taking Mounjaro. This is thought to be related to rapid weight loss rather than the medication itself. Hair typically regrows once weight loss stabilises. Ensuring adequate protein intake can help minimise hair loss.

Is Mounjaro safe long-term?

Mounjaro has been approved by the MHRA for use in the UK following extensive clinical trials. Long-term safety data from the SURMOUNT programme shows it is generally well-tolerated. As with any prescription medication, it should only be used under medical supervision.

Mounjaro Side Effects: Complete UK Guide (2026)

Phil Scaife

Updated: 26 March 2026

Like all medications, Mounjaro can cause side effects. Most are mild and temporary, but it's important to know what to expect. This guide covers all known side effects and how to manage them.

Mounjaro Side Effects: What You Need to Know

Mounjaro (tirzepatide) is a newer medication increasingly used in the UK to aid weight loss and help control type 2 diabetes. It works by affecting hormones that regulate appetite and blood sugar. While many people tolerate Mounjaro well, like all medicines, it can cause some side effects. This guide explains the common and less common side effects, how long they might last, and when to seek medical advice.

Common Side Effects

Studies and patient reports show that between 20-40% of people taking Mounjaro experience certain digestive system side effects as their body adjusts to the medication. These include:

Nausea: A feeling of sickness, sometimes leading to vomiting.
Vomiting
Diarrhoea: Loose or watery stools.
Constipation: Difficulty passing stools or infrequent bowel movements.
Stomach pain: Mild to moderate discomfort in the abdominal area.

These effects are quite common, especially in the early weeks of treatment. They are usually mild to moderate in intensity.

How Long Do Side Effects Last?

For most people, these side effects tend to improve over time. Generally, they last for about 2 to 4 weeks as your body gets used to Mounjaro. The NHS advises patients to keep their GP informed if side effects persist beyond this or become severe.

Remember, everyone's experience will be different, and some people may have minimal side effects while others take longer to adjust.

Tips to Reduce Nausea When Taking Mounjaro

Nausea is the most frequently reported side effect but there are practical ways you can reduce its impact:

Eat smaller, frequent meals: Rather than three large meals, try five or six smaller ones throughout the day to help ease upset stomach.
Avoid fatty or fried foods: These can worsen nausea, so opt for bland, easy-to-digest meals.
Stay hydrated: Drink plenty of fluids like water or herbal teas, but sip slowly to prevent feeling sick.
Rest if needed: Sometimes lying down with your head elevated can help ease nausea.
Speak to your GP: If nausea is severe, your doctor may suggest medications to help reduce it.

Less Common Side Effects

Aside from digestive symptoms, some patients may experience less common side effects such as:

Hair loss: Temporary thinning of hair may occur but often improves after stopping the drug.
Fatigue: Feeling unusually tired or low in energy.
Headaches: Mild to moderate headaches have been reported.

If you notice these symptoms, it's a good idea to discuss them with your GP to ensure they are related to Mounjaro and to rule out other causes.

Serious Side Effects to Watch For

While very rare, some serious side effects require immediate medical attention:

Pancreatitis: This is an inflammation of the pancreas. Symptoms may include severe abdominal pain that radiates to the back, nausea, and vomiting. Pancreatitis can be life-threatening if untreated.
Thyroid tumours: Animal studies have suggested a possible increased risk of thyroid C-cell tumours, but this has not been confirmed in humans. Symptoms such as persistent neck swelling, difficulty swallowing, or a hoarse voice should be checked.

If you experience any of the above, call NHS 111 or seek emergency care immediately.

Mounjaro and Alcohol

Currently, there is no direct contraindication between Mounjaro and alcohol use. However, alcohol can irritate your digestive system and contribute to nausea or vomiting, which may worsen Mounjaro side effects.

It is advisable to limit alcohol intake while your body adjusts to the medication. Discuss any concerns about alcohol and medication interaction with your GP or pharmacist.

When to Contact Your Doctor

It’s important to keep your GP informed during your treatment with Mounjaro. Contact your doctor if you experience:

Side effects that don’t improve after the first few weeks
Severe stomach pain, vomiting that won’t stop, or blood in stools
Symptoms suggesting pancreatitis or thyroid problems
Sudden and unexplained hair loss or intense fatigue impacting daily life

Your GP may adjust your dose, suggest ways to manage side effects, or decide if Mounjaro is the right treatment for you.

FAQs About Mounjaro Side Effects

1. Will everyone get side effects from Mounjaro?

No. Many people tolerate Mounjaro well with few or mild side effects. Around 20-

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Medically Reviewed by Kerris Lacy

This content has been reviewed for medical accuracy by Kerris Lacy, a qualified healthcare professional. Information provided is for educational purposes only.