Mounjaro is a prescription weight loss injection that contains tirzepatide. Like all medicines, it can cause side effects, especially when you first start treatment or when your dose is increased.

Headaches can occur with Mounjaro, but they are not usually the main side effect people report. More common side effects include nausea, vomiting, diarrhoea, constipation, and others. Some of these can indirectly make headaches more likely, especially if you are eating or drinking less than usual.

If you are getting headaches after starting Mounjaro, keep a note of when they happen, how severe they are, and whether they come with other symptoms. This can help your pharmacist or GP understand whether the headache may be linked to treatment, hydration, blood sugar, diet changes, or something unrelated.

Most headaches are not serious and can be managed at home. We recommend drinking plenty of water, resting, relaxing where possible, avoiding alcohol, and not skipping meals. Paracetamol or ibuprofen may help some people, but check with a pharmacist first if you are unsure whether they are suitable for you. You may also find it helpful to:

• Eat small, regular meals
• Drink water throughout the day
• Avoid alcohol if it worsens symptoms
• Limit very fatty or rich foods if they make nausea worse
• Rest in a quiet, dark room if the headache feels migraine-like
• Track whether headaches happen after injection day or dose increases

If you are vomiting, have diarrhoea, or cannot keep fluids down, speak to a pharmacist, GP, or NHS 111 for advice.

Do not stop or change your Mounjaro dose without speaking to your pharmacist, unless you have been told to do so in an emergency.

A mild headache may settle with fluids, food, rest, and simple pain relief. But if headaches are severe, keep coming back, or happen with other symptoms, you should contact your pharmacist or GP. Your prescriber may want to review your dose, side effects, hydration, food intake, blood pressure, or other medicines.

Get medical advice if your headache is not improving, keeps coming back, or feels unusual for you.

Ask for an urgent GP appointment or use NHS 111 if you have a headache with:

• Vision or eye problems
• Vomiting
• Jaw pain when eating
• A sore or tender scalp
• A headache triggered or made worse by coughing, sneezing, bending, or exercise
• Any symptoms you are worried about

Call 999 or go to A&E if you have a headache and:

• It starts suddenly and is extremely painful
• You have numbness or weakness in your face or body
• You have difficulty speaking, walking, balancing, or remembering things
• You have had a seizure
• You have had a recent head injury
• You are very drowsy, confused, or difficult to wake
• You have symptoms of meningitis, such as a stiff neck, high temperature, rash, or sensitivity to light

These warning signs are important whether or not you are taking Mounjaro.

You may be able to reduce the chance of headaches by keeping your routine steady during treatment. Try to:

• Drink enough fluids each day
• Eat regularly, even if portions are smaller
• Avoid skipping meals completely
• Reduce alcohol
• Get enough sleep
• Move up doses only when advised by your prescriber
• Tell your pharmacist if you feel dizzy, faint, weak, shaky, or unable to eat or drink normally

If you have diabetes, follow your clinician’s advice on blood sugar monitoring and what to do if your readings are low.

Headaches can happen while taking Mounjaro, but they may be caused by indirect effects such as eating less, dehydration, vomiting, diarrhoea, low blood sugar, or dose changes. Mild headaches often improve with fluids, food, rest, and suitable pain relief.

If your headache is severe, unusual, keeps returning, or comes with worrying symptoms, get medical advice. Your pharmacist or GP can help you decide whether it is likely to be related to Mounjaro and whether your treatment plan needs adjusting.