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Fast-changing safety information
Mounjaro safety advice can change as more people use it. This leaflet is based on UK product information and NHS/NICE guidance at the date shown below.
Last reviewed: 15 July 2026
Mounjaro can make appetite quieter. That can be helpful, but the aim is not to feel awful or to eat as little as possible. Side effects are common, especially when starting or increasing the dose. If symptoms are severe, persistent or worrying, ask for advice.
Quick Answer
The most common side effects are nausea, diarrhoea, vomiting, stomach pain and constipation. Reflux, burping, bloating, dry mouth, tiredness, injection-site reactions and hair shedding can also happen.
Side effects can become more noticeable after any dose increase. Symptoms often improve with time, slower eating, smaller portions, enough fluid and allowing symptoms to settle before a further increase.
Severe pain, repeated vomiting, dehydration or allergic symptoms need urgent advice.
Why Dose Changes Can Feel Hard
Mounjaro is increased gradually, but side effects can still become more noticeable after a dose increase. Individual responses vary.
This does not mean you have done anything wrong. Keep meals smaller, drink regularly and avoid very rich meals. If symptoms remain difficult, contact the prescribing team and do not increase the dose until they have settled or become manageable.
Common Side Effects
Feeling sick is common, especially early on or after a dose increase.
Eating less, drinking less or lower fibre can make this worse.
This can happen while your gut adjusts.
This often settles, but repeated vomiting needs advice.
Heartburn, bloating, gas and “sulphur burps” can happen.
This may be worse if you are eating and drinking less.
Sometimes linked to low intake, dehydration or rapid change.
This can happen after rapid weight loss or low nutrition.
Mild redness or itching can happen where the injection goes in.
What Usually Helps?
Most mild side effects can be managed with small changes. The aim is to support your body while it adjusts, not to push through severe symptoms.
Give fullness signals time to arrive. Stop when comfortably full.
Large or rich meals can make nausea, reflux and burping worse.
Sip fluids regularly. Dehydration can make you feel much worse.
Appetite may be quieter, but nutrition still matters.
A short walk can help constipation, bloating and reflux.
If side effects are difficult, ask before increasing.
Need More Detail?
This is the short version. If you are struggling with symptoms, read the more detailed guide: Managing Mounjaro side effects.
It has separate sections on nausea, constipation, diarrhoea, reflux, sulphur burps, dry mouth, tiredness and hair shedding.
When To Ask For Advice
Contact your prescriber, pharmacist or GP practice if:
- side effects are stopping you eating or drinking normally
- nausea, diarrhoea or constipation is not settling
- constipation comes with marked swelling, vomiting, severe abdominal pain, or inability to pass stool or wind—seek urgent advice
- you are unsure whether to increase the dose
- you have repeated vomiting
- you feel dizzy, faint, very weak or dehydrated
- you are taking insulin or a sulphonylurea and having low blood sugars
- you are due surgery or sedation
- you are pregnant, planning pregnancy, breastfeeding, or using oral contraception or oral progesterone as part of HRT
Seek Urgent Help
Stop and seek urgent medical advice if you have:
- severe, persistent stomach pain, especially if it goes through to your back, with or without vomiting
- repeated vomiting and you cannot keep fluids down
- signs of dehydration such as passing very little urine, confusion, fainting or extreme weakness
- swelling of the lips, tongue or throat, breathing difficulty, collapse, or a fast heartbeat with allergic symptoms
- severe right-sided upper tummy pain, fever, yellowing of the skin/eyes or dark urine
For severe, persistent abdominal pain that may spread to your back, stop taking Mounjaro and seek immediate medical help. This could be pancreatitis. If pancreatitis is confirmed, Mounjaro should not be restarted.
Use NHS 111 for urgent advice. Call 999 if there is immediate danger, severe allergic reaction, collapse or severe breathing difficulty.
A Note About Hair Shedding
Hair shedding can feel upsetting. It is not always caused directly by the medicine. It can happen after rapid weight loss, low calorie intake, low protein, low iron, illness or stress.
This is one reason we keep coming back to nutrition. Mounjaro may quieten appetite, but your body still needs enough protein, fibre, fluid, vitamins and minerals.
Dr Mel’s Notebook
Did you know?
Tummy side effects are most common when starting or increasing the dose. They can become more noticeable after any dose increase, although individual responses vary.
Try this today
At your next meal, eat slowly and stop at comfortably full rather than trying to finish the plate.
The evidence
The UK patient leaflet lists nausea, diarrhoea, vomiting, stomach pain and constipation as very common side effects.
Key Messages
- Side effects are common, especially early on or after dose increases.
- Side effects may become more noticeable after any dose increase.
- Severe nausea or being unable to eat is not a sign that treatment is working well.
- Eating slowly, smaller meals, fluids, protein and fibre can help.
- Ask for advice before increasing the dose if symptoms are difficult.
- Severe persistent abdominal pain, repeated vomiting, dehydration or allergic symptoms need urgent help.
New To Mounjaro?
Start with Starting Mounjaro: the basics for dosing, injection, storage and key safety information.
Useful Sources
Mounjaro KwikPen Patient Information Leaflet, emc
NICE: Prescribing, reviewing and stopping tirzepatide
First published July 2026. Last reviewed: 15 July 2026. Planned review: October 2026, or earlier if MHRA/NICE/product information changes.
Prepared for the Pathfields Healthy Living Portal.