Independent UK medicine guidance
Mounjaro sick-day rules: vomiting, diarrhoea and illness
A mild cold does not usually mean you need to change your Mounjaro. The concern is an illness that causes dehydration, persistent vomiting, diarrhoea or an inability to eat and drink normally. NHS sick-day guidance can vary according to why you take Mounjaro and what other medicines you use.
If you have vomiting or diarrhoea
Focus on hydration. Take small, frequent sips and consider asking a pharmacist about oral rehydration solution.
Do not take extra Mounjaro later to compensate for a delayed or missed injection.
The four-day missed-dose rule
The Mounjaro leaflet says:
| Situation | What the leaflet says |
|---|---|
| 4 days or less since due | Take it when remembered |
| More than 4 days | Skip it |
| Next dose | Take on the usual scheduled day |
| Minimum gap | Leave at least three days between two injections |
If illness means you miss more than one dose, ask your prescriber how to restart. Returning directly to a high dose after a longer break may increase side effects.
If you have diabetes
Illness can increase blood sugar even when you are eating less. Check your glucose more often if your diabetes team has advised you to monitor it.
Do not stop insulin. Insulin doses may need adjustment during illness, but this should follow your diabetes sick-day plan.
Other medicines, including metformin, SGLT2 inhibitors, sulphonylureas, diuretics and some blood-pressure tablets, may need special instructions during dehydrating illness.
Get medical help if:
- You cannot keep fluids down
- You are passing very little urine
- You have severe or persistent abdominal pain
- Your blood sugar remains very high or repeatedly low
- You have ketones or symptoms of ketoacidosis
- You are becoming confused, faint or unusually drowsy
- Symptoms are worsening or continue beyond 48 hours
Common questions
Should I skip my Mounjaro dose if I am ill?
Recent NHS guidance advises temporarily withholding tirzepatide during more than minor vomiting or diarrhoea, restarting after you have been eating and drinking normally for 24 to 48 hours. Confirm with your own clinician, because individual instructions can differ, and do not take extra later to compensate.
What is the four-day rule for a missed dose?
If it is four days or less since the dose was due, take it when remembered. If more than four days have passed, skip it and take the next dose on the usual scheduled day. Leave at least three days between two injections.
Do I stop my diabetes medicines when unwell?
Do not stop insulin. Illness can increase blood sugar even when eating less, and insulin doses may need adjustment following your diabetes sick-day plan. Other medicines such as metformin, SGLT2 inhibitors, sulphonylureas, diuretics and some blood-pressure tablets may need special instructions during dehydrating illness.
Related guides
Sources: Mounjaro Patient Information Leaflet (eMC) • Gloucestershire Hospitals medicines and dehydration guidance
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Sources referenced on this page
Linked from the text above:
- Mounjaro Patient Information Leaflet (eMC) www.medicines.org.uk
Standing primary references for every Monj page:
- Mounjaro (tirzepatide) Summary of Product Characteristics and Patient Information Leaflet, electronic medicines compendium
- MHRA Drug Safety Update: GLP-1 receptor agonists
- NICE TA1026: tirzepatide for managing overweight and obesity
- General Pharmaceutical Council register of pharmacies
- MHRA Yellow Card scheme
