Side effects
Mounjaro side effects: the symptom map
48 pages, one per symptom or situation. Each covers what is normal, what helps, and a plain three-level guide to when to get help.
Call 999 or go to A&E
Severe stomach pain which does not ease and may spread to your back, repeated vomiting, swelling of the face, lips or throat, trouble breathing, or a swollen painful belly with no wind or stools.
Call 111 or see a GP today
Vomiting or diarrhoea for more than 24 hours, little or no urine, fainting, a pounding heartbeat with dizziness, a spreading rash, pain under the right ribs after eating, or low blood sugar if you take insulin or a sulfonylurea.
Mention at your next check
Mild nausea, burps, constipation, tiredness, hair shedding, feeling cold, taste changes, or injection site redness which settles within a few days.
Urgent warning signs
Rare, but these are the pages to read if something feels seriously wrong.
- Mounjaro and pancreatitis: symptoms, risk and what to doAcute pancreatitis is an uncommon Mounjaro side effect, up to 1 in 100 people. If severe tummy pain spreads to your back, stop it and get urgent help.Covers urgent symptoms
- Mounjaro and cholecystitis: when gallbladder pain is an emergencyCholecystitis is an inflamed gallbladder, seen in 0.6% on Mounjaro in weight loss trials. Constant right-sided pain with fever or yellow skin needs A&E.Covers urgent symptoms
- Mounjaro and bowel obstruction (ileus): rare but seriousBowel obstruction and ileus are rare with GLP-1 medicines. No wind or stools, a swollen painful tummy and vomiting together need 999 or A&E the same day.Covers urgent symptoms
- Mounjaro allergic reaction: hives, swelling and anaphylaxisMild allergic reactions to Mounjaro are common, anaphylaxis is rare. Swelling of the lips, tongue or throat or trouble breathing means call 999 straight away.Covers urgent symptoms
- Mounjaro, your kidneys and dehydrationVomiting or diarrhoea on Mounjaro can dehydrate you and strain the kidneys. Drink steadily and get help the same day if you pass little or no urine.Covers urgent symptoms
Start here
3 pages- When to contact your Mounjaro prescriber, 111 or 999Call 999 for a swollen throat, trouble breathing or severe tummy pain into your back. Call 111 if fluids will not stay down. Raise mild side effects at review.Check if it persists
- How long do Mounjaro side effects last?Mounjaro stomach side effects peak after starting and after each dose increase, then ease within weeks. Hair shedding runs on a longer 3 to 6 month cycle.Usually manageable at home
- Mounjaro sick day rules: what to do when you are illIf illness gives you vomiting, diarrhoea or a fever, hold your Mounjaro dose, sip fluids and restart after 24 to 48 hours of eating and drinking normally again.Check if it persists
Injection and everyday
7 pages- How to use the Mounjaro KwikPen: step by stepFit a new needle, prime the pen, dial the dose, inject into your stomach or thigh and count slowly to 5. Each KwikPen holds 4 weekly doses for 30 days.Usually manageable at home
- Mounjaro injection site reactions: redness, lumps and itchingRedness and itching where you inject Mounjaro are common and fade in a few days. Rotate sites each week. Get help if the area turns hot, swollen or spreads.Usually manageable at home
- Mounjaro before surgery and anaesthesia: what to tell your teamTell your surgical team and anaesthetist you take Mounjaro. UK guidance says keep taking it before most planned operations and follow your fasting advice.Check if it persists
- Mounjaro and the contraceptive pill: the extra precaution you needMounjaro can make the pill less reliable. Use condoms or switch to a non-oral method for 4 weeks after starting and for 4 weeks after each dose increase.Check if it persists
- Mounjaro and pregnancy: planning, unexpected pregnancies and breastfeedingDo not use Mounjaro in pregnancy. Stop at least 1 month before trying to conceive. If you find out you are pregnant, stop and speak to a GP or midwife at once.Check if it persists
- Mounjaro in hot weather: storage, dehydration and dizzinessKeep unused Mounjaro pens in the fridge and in-use pens below 30C. In the heat, drink more than you think you need, as Mounjaro lowers thirst and intake.Check if it persists
- Norovirus and Mounjaro: managing a stomach bug on treatmentNorovirus on Mounjaro: hold your dose, sip fluids with rehydration salts and restart after 24 to 48 hours of normal eating. Call 111 if fluids do not stay down.Check if it persists
Stomach and digestion
6 pages- Mounjaro nausea and vomiting: causes, timing and reliefNausea is a very common Mounjaro side effect, reported by up to 1 in 3 people in SURMOUNT-1. It peaks after dose increases and eases over weeks for most.Check if it persists
- Mounjaro stomach pain: normal discomfort or a warning signMild tummy pain is a very common Mounjaro side effect. Severe pain to the back or under the right ribs may signal pancreatitis or gallstones.Check if it persists
- Mounjaro constipation: why it happens and what helpsConstipation is a very common Mounjaro side effect, affecting up to 17% of people in SURMOUNT-1. Fluids, fibre, movement and a short laxative course help most.Usually manageable at home
- Mounjaro diarrhoea: how long it lasts and how to manage itDiarrhoea is a very common Mounjaro side effect, seen in 19% to 23% of people in SURMOUNT-1. Most bouts ease within days. Fluids protect your kidneys.Check if it persists
- Mounjaro sulphur burps, bloating and acid refluxBurping, bloating, wind and reflux are common on Mounjaro, affecting up to 1 in 10 people. Smaller meals, earlier dinners and antacids or alginates help.Usually manageable at home
- Mounjaro and gastroparesis: delayed stomach emptying explainedMounjaro slows stomach emptying by design. Problem delays are uncommon, up to 1 in 100 people. Persistent vomiting or fullness after a few bites needs a GP.Check if it persists
Urgent warning signs
6 pages- Mounjaro and pancreatitis: symptoms, risk and what to doAcute pancreatitis is an uncommon Mounjaro side effect, up to 1 in 100 people. If severe tummy pain spreads to your back, stop it and get urgent help.Covers urgent symptoms
- Mounjaro, gallstones and your gallbladderGallstones are a common Mounjaro side effect in weight loss, tied to how much you lose. Pain under the right ribs lasting over 30 minutes needs urgent advice.Check if it persists
- Mounjaro and cholecystitis: when gallbladder pain is an emergencyCholecystitis is an inflamed gallbladder, seen in 0.6% on Mounjaro in weight loss trials. Constant right-sided pain with fever or yellow skin needs A&E.Covers urgent symptoms
- Mounjaro and bowel obstruction (ileus): rare but seriousBowel obstruction and ileus are rare with GLP-1 medicines. No wind or stools, a swollen painful tummy and vomiting together need 999 or A&E the same day.Covers urgent symptoms
- Mounjaro allergic reaction: hives, swelling and anaphylaxisMild allergic reactions to Mounjaro are common, anaphylaxis is rare. Swelling of the lips, tongue or throat or trouble breathing means call 999 straight away.Covers urgent symptoms
- Mounjaro, your kidneys and dehydrationVomiting or diarrhoea on Mounjaro can dehydrate you and strain the kidneys. Drink steadily and get help the same day if you pass little or no urine.Covers urgent symptoms
Energy, heart and blood sugar
7 pages- Mounjaro fatigue: why you feel tired and what helpsTiredness is a common Mounjaro side effect, often from eating less in the early weeks. Protein, fluids, sleep and a blood test for iron or thyroid usually help.Usually manageable at home
- Mounjaro dizziness and low blood pressureDizziness and low blood pressure are common on Mounjaro for weight loss. Weight loss and low fluids lower blood pressure, and some tablets may need a review.Check if it persists
- Mounjaro and a fast pulse: heart rate changes on tirzepatideTirzepatide raises resting heart rate by about 2 to 5 beats a minute on average. Palpitations with chest pain, breathlessness or fainting mean call 999.Check if it persists
- Mounjaro headaches: causes and reliefHeadaches on Mounjaro usually come from low fluids, skipped meals or less caffeine. Paracetamol is a safe first choice. A sudden severe headache needs 999.Check if it persists
- Mounjaro and low blood sugar (hypoglycaemia)Mounjaro rarely causes low blood sugar on its own. The risk rises with insulin or a sulfonylurea. Treat a reading below 4mmol/L with 15 to 20g of fast sugar.Check if it persists
- Mounjaro and diabetic eye changes: retinopathy cautionA fast fall in blood sugar on Mounjaro can briefly worsen diabetic retinopathy. If you have diabetic eye disease, keep up screening and report vision changes.Check if it persists
- Feeling cold on Mounjaro: why it happensFeeling cold is not a listed Mounjaro side effect but often follows eating less and losing fat. Cold with tiredness for weeks needs a thyroid and iron test.Usually manageable at home
Skin, hair and body
6 pages- Mounjaro hair loss: why hair sheds and when it grows backHair loss is a common Mounjaro side effect. In the weight loss trials 4.9% of people on tirzepatide reported it. Most cases are temporary shedding and regrow.Usually manageable at home
- Mounjaro face and loose skin: what changes and what helpsMounjaro face is a media name for facial volume loss after fast weight loss, not a listed side effect. What affects loose skin, and what helps.Usually manageable at home
- Mounjaro itching, rash and hives: what is normal and what is an emergencyItching or a rash at the injection site is common on Mounjaro. A spreading rash or hives can be an allergic reaction. Swelling of the lips or throat needs 999.Check if it persists
- Mounjaro skin pain and sensitivity: burning, tingling and tender skinMounjaro lists a change in skin sensation (dysaesthesia) as uncommon, up to 1 in 100 people. Why skin may burn, tingle or feel tender, and when to get it checked.Usually manageable at home
- Mounjaro muscle loss: protecting lean mass with protein and trainingIn SURMOUNT-1, about a quarter of weight lost on tirzepatide was lean mass. Protein at every meal and strength training on 2 days a week help you keep muscle.Usually manageable at home
- Mounjaro and periods: menstrual changes on treatmentPeriod changes are not a listed Mounjaro side effect, but weight loss can change cycles and restore ovulation. Why contraception matters and when to see a GP.Check if it persists
Mind, sleep and appetite
6 pages- Fear of injecting Mounjaro: getting past needle anxietyNeedle fear affects 20% to 30% of adults aged 20 to 40. How to make Mounjaro injections easier, from technique to applied tension, and where to get NHS help.Usually manageable at home
- Mounjaro low mood and anhedonia: feeling flat on treatmentSome people feel flat or low on Mounjaro. EMA and MHRA reviews found no causal link between GLP-1 medicines and suicidal thoughts. Where to get help.Check if it persists
- Mounjaro sleep problems and insomnia: causes and fixesInsomnia is not a listed Mounjaro side effect, but reflux, night hunger, nausea and caffeine all disturb sleep. Here are the causes and what helps each one.Usually manageable at home
- Mounjaro and food noise: why thoughts about food go quietMany people on Mounjaro say constant thoughts about food go quiet. What food noise means, why it fades, why it returns near dose day and how to use the quiet.Usually manageable at home
- Mounjaro taste changes and food aversionA changed sense of taste is an uncommon Mounjaro side effect (up to 1 in 100). Why food tastes different, which foods put people off and how to keep protein up.Usually manageable at home
- Mounjaro dry mouth and bad breath: causes and what helpsDry mouth and bad breath are not listed Mounjaro side effects, but low fluid intake, under-eating and reflux cause both. How to fix them and protect your teeth.Usually manageable at home
Eating and fluids
7 pages- Eating too little on Mounjaro: the under-eating trapMounjaro cuts appetite so hard some people barely eat. The signs of under-eating, a daily minimum to aim for and where to get help if eating feels out of hand.Check if it persists
- What to eat on Mounjaro injection dayOn Mounjaro injection day, eat small, plain, low-fat meals, keep sipping fluids and skip alcohol and fried food. Food ideas for dose day and the 2 days after.Usually manageable at home
- Eating out on Mounjaro: restaurants, portions and alcoholHow to eat out on Mounjaro: order a starter as a main, pick lower-fat dishes, take leftovers home and keep alcohol within 14 units a week. Pub and curry ideas.Usually manageable at home
- Fibre on Mounjaro: enough to keep things movingUK adults should aim for 30g of fibre a day, and smaller meals on Mounjaro make that harder. How to add fibre slowly, the best foods and why fluid matters.Usually manageable at home
- Mounjaro, iron, B12 and vitamin D: nutrients to watchSmaller meals on Mounjaro make iron, vitamin B12 and vitamin D harder to get. UK daily amounts, deficiency signs, food sources and when to ask for a blood test.Usually manageable at home
- Mounjaro electrolytes and sick day fluidsVomiting or diarrhoea on Mounjaro? Replace fluid and salts with small sips and oral rehydration sachets. What to drink, how much and when to call 111.Check if it persists
- Staying hydrated on Mounjaro: how much to drink and whyThe NHS advises 6 to 8 glasses of fluid a day, and on Mounjaro thirst often fades. Signs of dehydration, links to headaches and constipation, and habits to try.Usually manageable at home