Mounjaro electrolytes and sick day fluids

In short

Nausea, vomiting and diarrhoea each affect more than 1 in 10 people on Mounjaro
The SmPC warns dehydration from gut side effects can worsen kidney function, including acute kidney failure
Oral rehydration salts: one sachet in 200ml of water. Adults usually take 1 or 2 sachets after each loose stool. Follow the packet
Throw away made-up rehydration solution after 1 hour at room temperature or 24 hours in the fridge
Call 111 if vomiting lasts more than 2 days, diarrhoea more than 7 days, or you cannot keep fluids down

When you are vomiting or have diarrhoea on Mounjaro, the priority is replacing fluid and salts before you become dehydrated. Sip water or diluted squash little and often, and once you are losing a lot of fluid, switch to oral rehydration salts. Each sachet goes in 200ml of water, and adults usually take 1 or 2 sachets after each loose stool or vomit, as the packet says. The SmPC warns dehydration on tirzepatide can damage the kidneys. Call 111 if you cannot keep fluids down or your urine stays dark.

Why sick days matter more on Mounjaro

Nausea, vomiting and diarrhoea each affect more than 1 in 10 people on Mounjaro. They are most frequent during dose increases and ease over time. A stomach bug or food poisoning on top of the medicine adds to the losses.

The SmPC warns gut side effects can cause dehydration, which in turn can worsen kidney function, including acute kidney failure. It tells patients to take precautions to avoid fluid depletion and electrolyte disturbances, and notes older people may be more susceptible. The patient leaflet repeats this: avoid dehydration by drinking plenty of fluids.

Several things make the risk higher on Mounjaro:

You eat less, so you lose the fluid and salt food normally supplies
Thirst often falls, so you drink less without noticing
Diarrhoea and vomiting strip out sodium and potassium as well as water
Some common medicines add to the strain on the kidneys when you are dehydrated (see below)

The kidneys and dehydration page covers kidney risk in more depth.

What electrolytes are

Electrolytes are salts dissolved in your blood, mainly sodium, potassium and chloride. They control fluid balance, nerve signals and muscle contraction, including the heart. Diarrhoea removes large amounts of sodium and potassium. Vomiting removes acid and chloride.

Plain water replaces fluid but not salts. Drinking large amounts of water alone during heavy diarrhoea can dilute the sodium in your blood further. Oral rehydration salts contain glucose, sodium and potassium in a balance designed to be absorbed quickly from the gut.

What to drink and when

Situation	What to drink	How
Feeling sick but not vomiting	Water, diluted squash, weak tea, ginger or peppermint tea	Small sips every few minutes
Vomited once or twice	Water or diluted squash	Let the stomach settle, then start with a few sips and build up
Repeated vomiting or diarrhoea	Oral rehydration solution	1 or 2 sachets (200 to 400ml) after each loose stool or vomit, plus water between
Recovering	Water, squash, clear soup, then normal drinks	Aim for pale yellow urine

The NHS advises starting with small sips if you feel sick and gradually drinking more. Large gulps stretch a stomach Mounjaro has already slowed and often come straight back up.

Using oral rehydration salts

Oral rehydration sachets are sold without a prescription. NHS hospital guidance on using them:

Mix one sachet with 200ml of tap water. The amount of water matters, because too much or too little upsets the balance of salts.
Do not mix with milk or juice, and do not add sugar or salt.
Drink 1 or 2 sachets after each loose stool, as the adult dose on the packet says. If you cannot finish it at once, sip it over about 30 minutes.
If you are sick within 30 minutes of drinking it, take another dose.
Throw away any made-up solution after 1 hour at room temperature, or after 24 hours in the fridge.
Do not use it for more than 2 to 3 days unless a doctor advises it.

Check with a pharmacist or your doctor before using rehydration salts if you have diabetes (the sachets contain sugar), kidney disease or liver disease. Chilling the solution often makes it easier to drink.

Drinks to avoid when you are ill

Alcohol, which adds to dehydration and nausea
Fizzy drinks and fruit juice, which the NHS says can make diarrhoea worse
Strong coffee and energy drinks
Sports drinks and flat cola as a substitute for rehydration salts. They contain too much sugar and too little salt.

Eating on a sick day

You do not need to eat while you are actively vomiting. The NHS advises eating when you feel able. Start with small portions of plain food:

Dry toast or plain crackers
A small portion of plain rice or pasta
A banana, which also supplies potassium
Clear soup or broth, which supplies salt and fluid
Plain yoghurt, once you feel better

Avoid fatty, fried and spicy food until you have kept normal meals down for a day.

Your other medicines

When you are dehydrated, some common medicines can strain the kidneys or build up in the body. These include metformin, SGLT2 inhibitors such as dapagliflozin and empagliflozin, diuretics (water tablets), ACE inhibitors such as ramipril, ARBs such as losartan, and anti-inflammatory painkillers such as ibuprofen. Ask your GP or pharmacist whether any of yours should be paused on a sick day. Do not stop a medicine without advice. The sick day rules page explains this in full.

If you take an oral contraceptive, vomiting or severe diarrhoea can stop it working. Check your pill leaflet and see Mounjaro and the contraceptive pill.

Your next injection

If you are unwell on injection day, speak to your prescriber. The leaflet allows a missed dose to be taken up to 4 days (96 hours) late. After that, skip it and take the next one on your usual day. Never take two doses within 3 days of each other.

When to get help

Call 999 or go to A&E if:

You are vomiting blood, or vomit looks like coffee grounds or is green
You have sudden severe stomach pain, or pain going through to your back
Your skin, lips or tongue look blue, grey, pale or blotchy, or your skin is cold
You are confused, very drowsy or hard to wake
You are breathing fast or struggling to breathe

Call 111 or see a GP today if:

You cannot keep any fluids down
Your urine is dark yellow, or you are peeing much less than usual
You feel dizzy on standing and it does not pass, or your heart is racing
Vomiting has lasted more than 2 days, or diarrhoea more than 7 days
You have blood in your diarrhoea or bleeding from your bottom
You still have signs of dehydration after using rehydration salts

Mention at your next check if:

Vomiting or diarrhoea happens after every dose increase
You want a written plan for which medicines to pause on sick days
You are older or have kidney problems and want your kidney function checked

The NHS advises staying off work until you have had no vomiting or diarrhoea for 2 days if a bug is the cause. For bugs on Mounjaro, see norovirus and Mounjaro. Report side effects through the MHRA Yellow Card scheme.

Questions people ask

What should I drink if I am being sick on Mounjaro?

Start with small sips of water, diluted squash or oral rehydration solution every few minutes, then build up as you keep them down. Once you are losing a lot of fluid through vomiting or diarrhoea, oral rehydration salts replace the sugar, salt and potassium plain water cannot. Avoid alcohol, fizzy drinks and fruit juice.

How much oral rehydration solution should I drink?

Follow the packet. Each sachet is made up with 200ml of water. Adults usually take 1 or 2 sachets after each loose stool or each time they are sick. If you cannot drink it all at once, sip it over about 30 minutes. If you have diabetes, kidney disease or liver disease, check with a pharmacist or your doctor first.

Should I take my Mounjaro injection if I am ill?

Speak to your prescriber. The leaflet allows a dose to be taken up to 4 days late, so a short delay while you recover is possible within the rules. Do not take two doses within 3 days of each other, and do not stop treatment for longer without advice.

Can dehydration on Mounjaro damage my kidneys?

Yes. The SmPC warns dehydration from nausea, vomiting and diarrhoea can worsen kidney function, including acute kidney failure, and says older people may be more at risk. Peeing much less than usual, dark urine and dizziness on standing are warning signs.

Are sports drinks or flat cola as good as rehydration salts?

No. They contain too much sugar and too little salt to replace what diarrhoea removes, and the NHS advises avoiding fizzy drinks and fruit juice when you have diarrhoea. Use oral rehydration sachets from a pharmacy or supermarket instead.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Mounjaro electrolytes and sick day fluids. Site: Mounjaro Info (https://mounjaroinfo.co.uk/side-effects/mounjaro-electrolytes-and-sick-day-fluids/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

Vomiting and diarrhoea are very common on Mounjaro (tirzepatide), and the SmPC warns the fluid loss can cause dehydration and harm kidney function, including acute kidney failure. When you are sick, sip fluids little and often, use oral rehydration salts made up with 200ml of water after each loose stool or vomit, and call 111 if you cannot keep fluids down or your urine stays dark.

Nausea, vomiting and diarrhoea each affect more than 1 in 10 people on Mounjaro
The SmPC warns dehydration from gut side effects can worsen kidney function, including acute kidney failure
Oral rehydration salts: one sachet in 200ml of water. Adults usually take 1 or 2 sachets after each loose stool. Follow the packet
Throw away made-up rehydration solution after 1 hour at room temperature or 24 hours in the fridge
Call 111 if vomiting lasts more than 2 days, diarrhoea more than 7 days, or you cannot keep fluids down

Cite as: Mounjaro Info, "Mounjaro electrolytes and sick day fluids", https://mounjaroinfo.co.uk/side-effects/mounjaro-electrolytes-and-sick-day-fluids/, reviewed 22 October 2026.