Medical Oncologist
Gut and hydration
Rehydration and ORS during chemotherapy
When someone on chemotherapy is losing fluid through loose motions or vomiting, oral rehydration solution replaces the salts as well as the water, which plain water cannot do. It is cheap and available everywhere. This page covers how to mix and give it properly, what else counts as fluid, how to make it at home, and the point at which home management has to stop.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
Is ORS the right thing to drink during chemotherapy?
When someone on chemotherapy is losing fluid through loose motions or vomiting, oral rehydration solution is usually better than plain water, because it replaces the salts going out as well as the water. A sachet from the chemist, mixed exactly as the packet says, is cheap and widely available.
Two cautions, and both matter. Check with your team first if there is heart or kidney disease, because the salt load is not right for everyone. And ORS is for keeping up with losses at home — it is not a substitute for going in when the losses have outrun what anyone can drink.
Why this page exists
Dehydration is one of the commonest reasons people on chemotherapy end up admitted, and a large share of those admissions are preventable. The fluid goes out quietly over two or three days while the family is focused on the food that is not being eaten.
Judge it by urine, not by how the person says they feel. Pale and passed regularly is what you want to see.
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When to stop managing it at home
Go to the nearest emergency department the same day, saying clearly that the person is on chemotherapy, if there is a fever, if loose motions are frequent and not slowing, if vomiting means nothing stays down, if little or no urine has been passed since the morning, or if the person is drowsy, confused or dizzy on standing. Do not start an anti-diarrhoeal from home when there is a fever — that combination is dangerous, and it is covered on the linked page.
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Making and giving rehydration fluid properly
Getting the mixing right matters more than people expect. A stronger solution does not rehydrate faster; it does the opposite.
Use the whole sachet in the stated amount of water
Read the packet and measure the water rather than guessing with a glass. Half a sachet in half the water is not the same thing, and a concentrated mix pulls fluid into the gut and makes loose motions worse.
Use safe water
Boiled and cooled, or bottled. During the low-count days the gut is far more vulnerable to anything in the water, and an infection on top of the existing problem is exactly what you are trying to avoid.
Give it cool, in small amounts, often
A few sips every ten or fifteen minutes stays down far better than a glass at once, particularly if there is sickness. Set an alarm rather than relying on anyone remembering.
Make a fresh batch each day
Keep it covered and refrigerated, and throw away what is left at the end of the day. Do not add sugar, salt, lemon or anything else to improve the taste — the balance is the point of it.
Keep a written tally
Glasses in, and roughly how many times the person passed motions or urine. A sheet of paper on the fridge. This is the single most useful thing to take to the clinic or the emergency department.
What else counts
Other fluids that help, and ones that work against you
ORS is the main tool when losses are heavy. The rest of the day still needs filling.
Good choices through the day
Plain boiled and cooled water, thin buttermilk, tender coconut water, rice kanji water, thin dal water, and diluted milk if it is tolerated. Cool rather than hot, and sipped rather than gulped.
Bonus
- Kanji water carries a little energy too
- Buttermilk is easier than plain curd on a bad gut
Better avoided while losses are heavy
Fizzy drinks, packaged fruit juices, very sweet sherbets and strong coffee or tea. Sugary drinks pull water into the gut and can make loose motions worse, and caffeine adds to the fluid going out.
Sports drinks are not the same as ORS. The salt and sugar balance is different.Food that carries fluid
Curd rice, plain khichdi, kanji, soft banana and stewed apple all put fluid in alongside something to absorb. Small amounts often is the pattern, and bland is deliberate while the gut settles.
When vomiting is the main problem
Very small sips, ice chips sucked slowly, and anything cold rather than warm. If your team has given anti-sickness medicine, use it as they directed rather than only when things are already bad.
Report it if
- Nothing has stayed down
- The medicine is not working
If you cannot get a sachet
Can you make rehydration fluid at home?
You can, and generations of families have. The traditional home version is a measured amount of sugar and a much smaller measured amount of salt dissolved in a litre of boiled, cooled water. Your team or your local pharmacist can give you the exact measures, and it is worth asking them to write it down for you.
Why the sachet is still better
A packet is already balanced and does not depend on anyone's spoon. The commonest mistake at home is too much salt, which makes dehydration worse rather than better, and that mistake is harder to make with a sachet. Keep a few in the house from the start of treatment rather than sending someone out at midnight.
Rice kanji water deserves a mention
The water drained from well-cooked rice, lightly salted and cooled, is a reasonable everyday fluid when the gut is unsettled, and most households can make it without going anywhere. It is not a replacement for ORS when losses are heavy, but it is far better than nothing and it is usually accepted when other things are refused.
Ask your team for the home recipe and the measures before you need them. Writing it on the fridge now saves a bad night later.Leave a number, we will call you
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Being straight with you
What this page cannot tell you
It cannot tell you how much fluid you should be drinking. That depends on body size, the weather, what the treatment is doing to the kidneys, and whether there is heart or kidney disease in the background. In some of those conditions drinking more is actively unsafe, so this is a question for your own team rather than a number from a page.
It also cannot tell you whether ORS is suitable for you, or how often to take it. And it cannot tell you why the losses are happening. Loose motions during chemotherapy can be the drugs, an infection, or something unrelated, and those are managed very differently. An infection in particular must not be treated with an anti-diarrhoeal at home.
What to do next
Keep ORS sachets and safe drinking water in the house from the start of treatment. Start the written tally today if there is any loose motion or sickness. Ask your team at the next visit what your own fluid target is and whether ORS suits you, so the answer is settled before you need it.
Questions we are asked
Common questions about rehydration
Is ORS safe for everyone on chemotherapy?
For most people yes, but not all. The salt and sugar content matters if there is heart failure, kidney disease or diabetes, and those need your team's advice first. Ask once, early in treatment, so you know the answer before a bad night rather than deciding at the chemist counter.
Can I just drink more water instead?
Water alone is fine for ordinary dryness. When fluid is being lost through loose motions or vomiting, salts go out with it, and replacing water without them does not correct things properly. That is the situation ORS is designed for. For everyday sipping, plain water is perfectly good.
Are sports drinks or packaged juices a reasonable substitute?
Not really. Sports drinks carry a different salt and sugar balance, and packaged juices are usually very sweet, which can pull water into the gut and worsen loose motions. If you cannot get a sachet, ask your team for the home recipe rather than reaching for a bottled drink.
How do I know if the rehydration is working?
Urine is the clearest guide — passed regularly and pale rather than dark and scanty. Alongside that, the person should feel less dizzy on standing and less muddled. If urine is still scanty after a day of trying, the losses are outrunning what you can give and it is time to go in.
She vomits the ORS straight back up. What now?
Go smaller and slower — a spoonful every few minutes, cold, or ice chips sucked slowly. If nothing at all is staying down over several hours, stop trying to manage it at home and go in. Fluid into a vein is straightforward and it corrects the problem quickly.
Should I take an anti-diarrhoeal so the fluid stays in?
Not without your team saying so, and never if there is a fever. Taking one when an infection is causing the loose motions traps the infection in the gut and can make matters considerably worse. This is one of the few genuinely dangerous self-medication decisions during chemotherapy.
Does coconut water count as ORS?
Tender coconut water is a good fluid and most people tolerate it well, but its salt balance is not the same as a rehydration sachet, so it does not replace ORS when losses are heavy. Use it as one of the fluids through the day rather than as the main treatment for significant losses.
How long should we keep this up at home?
Only while the person is clearly keeping up — passing urine normally, not feverish, and the losses are settling rather than increasing. If a day of careful rehydration has not turned things around, or anything on the warning list appears, that is the point to contact the team rather than continue.
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Sources
- World Health Organization — Oral rehydration salts
- Cancer Research UK — Diarrhoea and cancer drugs
- Macmillan Cancer Support — Bowel changes during cancer treatment
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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