Independent UK medicine guidance
Mounjaro side effects: interactive UK symptom map
Mounjaro can cause side effects, but not everyone gets them. Stomach and bowel symptoms are the most common and are often most noticeable when treatment begins or the dose increases. Use the body map to explore possible effects and see when a symptom needs medical help. It cannot diagnose the cause of a symptom.
Explore side effects by body area
Select a body area to see what may happen, what may help with mild symptoms, and when to get help. Frequencies come from the current UK patient information leaflet.
Select a side effect to explore
Select a side effect to begin
Tap a point on the body, or choose a body area from the list, to see what may happen, what may help with mild symptoms, and when to get help.
This tool is general information only. It is not medical advice and it cannot diagnose you. If a symptom worries you, speak to your prescriber, pharmacist or GP. Use NHS 111 for urgent concerns. In an emergency, always call 999.
Head & nervous system
Common to uncommon, depending on symptom- What may happen
- Dizziness and tiredness are common. Changed taste and altered skin sensation are uncommon. Headache, drowsiness, weakness, confusion, hunger, sweating and a fast heartbeat can be warning symptoms of low blood sugar rather than listed side effects in their own right.
- What may help with mild symptoms
- Eat and drink regularly if possible. If you monitor blood glucose, follow the hypo plan agreed with your diabetes team.
- When to get help
- Low blood sugar is mainly a concern when Mounjaro is used with insulin or certain other diabetes medicines. Severe or recurrent symptoms need clinical advice. If someone is unconscious or not responding normally, call 999.
Source: UK patient information leaflet (eMC) • NHS: low blood sugar
Hair & skin
Hair loss & skin reactions: common • severe allergy: rare- What may happen
- Hair loss, rash, itching and eczema can occur. In pooled weight-management studies, hair loss was reported in 4.9% of tirzepatide participants and 1.0% of placebo participants; events were mainly mild and most recovered while continuing treatment.
- What may help with mild symptoms
- Contact a pharmacist or prescriber if rash, itching or hair loss is troublesome or does not settle.
Call 999: rapid swelling of the lips, tongue or throat, trouble swallowing or breathing is an emergency.
Read the full guide to skin pain & sensitivityMouth, throat & breathing
Severe allergic reactions: rare (up to 1 in 1,000)- What may happen
- Breathing problems, rapid swelling of the lips, tongue or throat, difficulty swallowing and a fast heartbeat can be signs of a severe allergic reaction such as anaphylaxis or angioedema.
Call 999 now. Do not wait, and do not complete the rest of this page first. Severe allergic reactions are an emergency.
Source: NHS: anaphylaxis • UK patient information leaflet (eMC)
Pulse, dizziness & blood pressure
Dizziness & low blood pressure: common in weight management- What may happen
- A faster pulse (common in type 2 diabetes studies, uncommon in weight management), dizziness or feeling faint, particularly alongside dehydration, reduced food and fluid intake, low blood pressure or low blood sugar.
- What may help with mild symptoms
- Sit or lie down if dizzy and stand up slowly. Check food and fluid intake has not become too low. Do not drive, cycle or use machinery while dizzy or if vision is affected.
- When to get help
- Persistent faintness or a racing pulse needs prescriber advice. Collapse, severe breathing difficulty or chest pain needs 999.
Stomach & pancreas
Nausea, vomiting & abdominal pain: very common • pancreatitis: uncommon- What may happen
- Nausea, vomiting and abdominal pain are very common in weight management, can be most noticeable during dose escalation, and often reduce over time. Acute pancreatitis is uncommon (up to 1 in 100).
- What may help with mild symptoms
- Smaller, lower-fat meals; eat slowly and stop when comfortably full; avoid lying down immediately after eating; take regular small sips of fluid.
Warning sign of pancreatitis: severe, persistent abdominal pain, with or without nausea or vomiting, especially pain spreading to the back. Stop using Mounjaro and seek urgent medical help. Do not restart if pancreatitis is confirmed. The MHRA strengthened this warning in January 2026 following rare reports of necrotising and fatal pancreatitis.
Read the full guide to pancreatitis warning signsSource: MHRA Drug Safety Update, January 2026 • UK patient information leaflet (eMC)
Gallbladder
Gallstones: common in weight management • inflammation: uncommon- What may happen
- Severe upper abdominal pain, potentially under the right ribs. Gallbladder illness can also involve fever, vomiting or jaundice. In weight-management studies, acute gallbladder events were positively correlated with the amount of weight reduced.
- When to get help
- This page cannot tell you whether pain is gallstones. Severe abdominal pain needs urgent assessment.
Urgent: contact NHS 111 for severe gallbladder-type pain, and use 999 or A&E if someone is acutely very unwell.
Bowel & digestion
Diarrhoea & constipation: very common- What may happen
- Diarrhoea and constipation are very common in weight management. Indigestion, bloating, burping, wind and reflux are common. Delayed stomach emptying is uncommon.
- What may help with mild symptoms
- Fluids little and often; smaller meals; lower-fat foods; stay upright after eating. A pharmacist can advise on oral rehydration, constipation or reflux treatment suitable for you personally.
- Before your next dose increase
- If digestive symptoms have not settled, contact your prescriber before the next planned increase. Do not change the dose yourself.
Use NHS 111 if you keep vomiting and cannot keep fluid down, remain dehydrated after oral rehydration, have bloody diarrhoea, or symptoms are severe. Persistent vomiting and diarrhoea can cause dehydration and may worsen kidney function.
Read the full guide to constipation reliefSource: UK patient information leaflet (eMC) • NHS: diarrhoea and vomiting
Injection site
Itching/redness: common • pain: uncommon- Where to inject
- The UK leaflet recommends the stomach area (at least 5cm away from the belly button), the front of the thigh, or the back or side of the upper arm, which is usually easiest when someone else gives the injection. The pink map shows all three recommended areas. Switch to a different site or spot with each weekly dose.
- What may happen
- Redness, itching, tenderness or pain at the injection site. Redness can be harder to see on brown or black skin, so also watch for warmth, swelling, tenderness and skin texture change.
- What may help with mild symptoms
- Use a different spot within the recommended injection areas each week, at least one finger width from the last injection. If you also inject insulin, use a different site for the insulin.
- When to get help
- Contact a pharmacist or prescriber if a reaction is worsening, spreading, very painful, hot, producing discharge or not settling.
Call 999 if an injection reaction occurs together with throat swelling or breathing difficulty.
Read the full guide to skin pain & sensitivityQuick safety check
An optional four-question check that routes you to the right UK next step. It asks nothing personal, stores nothing, and cannot identify the cause of your symptoms.
What the frequency words mean
Frequency can differ according to whether Mounjaro is used for weight management or type 2 diabetes and which other medicines are taken. These bands describe groups of people; they do not predict what will happen to one person.
Side effects at a glance
| Frequency | Side effects (weight management, current UK leaflet) |
|---|---|
| Very common | Nausea, diarrhoea, vomiting, abdominal pain, constipation |
| Common | Indigestion, abdominal bloating, burping, wind, reflux/heartburn, fatigue, hair loss, injection-site reactions, dizziness and low blood pressure, gallstones |
| Uncommon | Acute pancreatitis, injection-site pain, changed taste, altered skin sensation, delayed stomach emptying, gallbladder inflammation or infection |
| Rare | Severe allergic reactions such as anaphylaxis and angioedema |
Low blood sugar is listed separately because the risk depends strongly on other diabetes medicines, and is especially associated with insulin or sulphonylureas. Warning symptoms can include headache, drowsiness, weakness, dizziness, hunger, confusion, irritability, fast heartbeat and sweating. Follow the hypo plan supplied by your diabetes team; if someone is unconscious or not responding normally, call 999.
After starting or increasing a dose
There is no exact timetable for an individual. Do not increase again until your prescriber’s schedule allows, and speak to them if side effects have not settled.
What helps with mild symptoms?
Nausea & vomiting
Try smaller, lower-fat meals. Eat slowly and stop when comfortably full. Cold or bland foods may be easier. Avoid lying down just after eating. Take small, regular sips rather than a large drink at once. A pharmacist can advise on oral rehydration.
Red flag: severe, persistent abdominal pain (especially spreading to the back) needs urgent medical help, and use NHS 111 if fluids will not stay down.
Diarrhoea
Replace lost fluid with small, regular drinks. A pharmacist can advise whether an oral rehydration solution is appropriate for you.
Red flag: use NHS 111 if dehydration persists, there is blood in your stool, or you cannot keep fluids down.
Constipation
Drink regularly, move as you are able, and add suitable fibre gradually rather than suddenly. Ask a pharmacist which treatment is suitable for you; do not stack multiple laxatives on your own.
Red flag: severe pain, vomiting, marked swelling or being unable to pass stool or wind needs prompt assessment rather than more self-treatment.
Bloating, burping & reflux
Smaller meals, eating slowly, reducing fizzy drinks, staying upright after eating and reducing your personal triggers (such as very fatty or spicy meals) may help. A pharmacist can advise on a suitable treatment.
Red flag: persistent burping or reflux with severe pain, vomiting or marked bloating needs clinical advice.
Fatigue & dizziness
Check that food and fluid intake have not become too low. Stand up slowly. Do not drive, cycle or use machinery if dizzy or if vision is affected. Diabetes or blood-pressure medicines may need review by a clinician.
Hair loss
Hair loss is listed as common in weight management and in pooled studies was mainly mild, with most people recovering while continuing treatment. Weight loss itself, dietary intake and other health factors can also affect hair. Persistent or marked shedding warrants clinical review.
Injection-site reactions
Rotate the exact injection spot within the approved area each week. Monitor warmth, swelling, tenderness and texture change as well as colour, which can be harder to see on brown or black skin. Escalate to a pharmacist or prescriber if a reaction is spreading, hot, very painful, discharging or persistent.
Evidence checks: headaches, insomnia & mood
Headaches
Headache is not listed as a direct side effect in the current UK leaflet; it appears there as a possible warning symptom of low blood sugar. NHS hospital guidance notes dehydration, low glucose or dietary change may contribute. Persistent or severe headaches deserve clinical review on their own merits.
Insomnia
Sleep disturbance is not a listed adverse reaction in the current UK leaflet. Reflux, hunger changes and low blood sugar symptoms are plausible contributors for some people, but a causal link is not established. Discuss persistent sleep problems with a clinician.
Depression & suicidal thoughts
After a comprehensive safety review, the MHRA concluded that available evidence did not support a causal link between GLP-1 medicines and depression, suicidal ideation or suicide. That is not the same as saying risk is zero for any individual. Any suicidal thoughts or immediate mental-health danger need urgent help regardless of the suspected cause: call 999 in an emergency, or use the appropriate NHS urgent mental-health route.
Where to get help in the UK
Suspected anaphylaxis, severe breathing or swelling symptoms, collapse or unresponsiveness.
NHS anaphylaxis guidanceSerious suspected side effects, severe or persistent abdominal pain, unable to keep fluids down, ongoing dehydration, or accidental overdose.
NHS 111 online • Call 111Side effects that bother you, persist, recur, or make you unsure about taking the next scheduled dose.
Report a suspected side effect, including one not in the leaflet. Yellow Card cannot give medical advice and does not replace seeking care.
Report via Yellow CardRelated Monj guides
- Pancreatitis: warning signs & facts
- Gallstones & gallbladder guide (coming soon)
- Severe allergic reaction guide (coming soon)
Frequently asked questions
What are the most common Mounjaro side effects?
For weight management, nausea, diarrhoea, vomiting, abdominal pain and constipation are listed as very common, meaning more than 1 in 10 people may be affected. Indigestion, bloating, burping, wind, reflux, tiredness, hair loss and injection-site reactions are among the common effects. Not everyone gets side effects, and one person’s experience cannot be predicted from a frequency band.
When do Mounjaro side effects usually start?
Digestive side effects can appear after starting treatment or after a dose increase. Clinical-trial data show that nausea, vomiting and diarrhoea occurred more often during dose escalation and decreased over time. There is no exact timetable for an individual.
How long do Mounjaro side effects last?
The UK leaflet says the main digestive effects are usually not severe, are most common when starting tirzepatide and decrease over time in most patients. Some people have longer-lasting or recurrent symptoms. A symptom that is severe, worsening, worrying or not going away should be discussed with a pharmacist, prescriber or doctor.
Are side effects worse on higher doses?
They can become more noticeable after a dose increase. In type 2 diabetes studies, gastrointestinal adverse reactions increased with dose, while weight-management studies showed high gastrointestinal rates across 5 mg, 10 mg and 15 mg. Dose alone does not predict an individual’s experience. Do not change the dose without your prescriber.
Should I take my next dose if I still have side effects?
It depends on the symptom, its severity and your medical history, so there is no blanket answer. Contact your prescriber or pharmacist before the next dose if symptoms are severe, persistent or making you uncertain. Severe persistent abdominal pain that could be pancreatitis requires stopping Mounjaro and urgent medical assessment.
What does pancreatitis pain feel like?
The official warning is severe, persistent pain in the abdomen that may spread to the back and may occur with nausea or vomiting. This cannot be diagnosed online. Stop using Mounjaro and seek urgent medical help if these symptoms occur.
Can I drink alcohol while taking Mounjaro?
NHS guidance says it is best to avoid alcohol because it can increase side effects such as nausea and vomiting. Alcohol can also complicate low blood sugar risk in people using diabetes medicines. Advice should take account of your own health and medicines.
Can I report a side effect myself?
Yes. Patients, carers and health professionals can report suspected side effects to the MHRA Yellow Card scheme, even if the effect is not in the leaflet. A Yellow Card report does not prove the medicine caused the event, and the service cannot give medical advice. Seek medical help separately when needed.
Explore other side effects
Tap a point on the body to jump to that symptom, or choose from the full list below. The pink marker shows where you are now.
