Before the Bug Arrives: The Sick-Day Conversation to Have About Your Regular Medicines

It's usually 2am when it happens. You've been up half the night with a stomach bug, you can't keep water down, and your pill box is sitting on the kitchen counter with a question mark over it. Do you take the blood pressure tablets? Skip them? What about the metformin?

That is a genuinely difficult question to answer in the moment, in the dark, feeling awful. Which is why the best time to sort it out is now — on a normal afternoon, before anything has gone wrong.

What 'sick-day rules' actually means

It's a term you'll hear from pharmacists, diabetes teams and kidney specialists. In plain terms, it's a personal plan for what to do with your medicines when illness disrupts the normal rhythm — vomiting, diarrhoea, a high fever, or simply not being able to eat and drink properly.

There's no single national rulebook that fits everyone. A fit 40-year-old on one tablet has a very different picture from an 80-year-old on eight. That's why the answer is a conversation, not a leaflet.

Why dehydration changes the maths

When you're vomiting or running a temperature, you lose fluid and salts. Blood volume drops, and the kidneys respond by holding on to what they can. Now add medicines on top.

• Diuretics (think furosemide, bumetanide, indapamide, or the thiazide in your blood pressure pill) push more fluid out. During a vomiting bug, that's the opposite of helpful.
• ACE inhibitors and ARBs — names ending in -pril or -sartan — reduce pressure inside the kidney's filtering system. Usually protective. During dehydration, less so.
• NSAIDs like ibuprofen and naproxen, whether prescribed or bought over the counter, narrow the blood vessels feeding the kidneys.

Put those three together during a bout of diarrhoea and you have what clinicians sometimes call a "triple whammy" — a well-recognised setup for acute kidney injury. It's not rare, and it's often avoidable with a bit of planning.

This doesn't mean those medicines are bad. It means they need adjusting for a few days when you're genuinely unwell — and only on advice.

Diabetes: a different set of moving parts

For people with diabetes, illness tends to push blood glucose up, sometimes sharply. Meanwhile:

• Metformin carries a small risk of a serious complication called lactic acidosis when kidneys are struggling, so it's often paused during significant dehydration.
• SGLT2 inhibitors (names ending in -flozin) need particular care in illness — they can, rarely, trigger a dangerous condition even when glucose looks normal.
• Insulin should never be stopped because you're not eating. In fact, illness usually increases the need for it. This is one of the most important things to get clear in advance.
• Sulfonylureas such as gliclazide can drop blood sugar too low if you're not eating.

If you use insulin and you're ill, you need a proper sick-day plan from your diabetes team — not guesswork.

Steroids: the one you don't stop on your own

If you take prednisolone or another steroid for more than a few weeks, your body has adapted to it. Stopping suddenly — even because you feel too sick to swallow the tablets — can cause a serious adrenal problem.

For some people, steroid doses actually need increasing during illness. For others, not. Either way, that's a decision for the clinician who knows your history, and it's worth having the answer written down before you need it.

If you're sick straight after taking a tablet

A very common worry. The general principle is: don't double up. If a dose comes straight back up, you don't automatically take another. Repeated vomiting also means tablets may not be absorbed at all — which matters for things like epilepsy medicines, thyroid tablets and blood thinners. Ring your pharmacist or NHS 111 for guidance rather than improvising.

The five questions to ask at the counter

Next time you collect a prescription, take two minutes:

1. Which of my medicines might need pausing if I'm vomiting or can't keep fluids down?
2. Which ones must I never stop, even for a day?
3. What should I do if I'm sick within an hour of taking a dose?
4. How much fluid should I be aiming for, and should I use oral rehydration salts?
5. When should I stop managing this at home and call for help?

Ask the pharmacist to write the answers on the back of your repeat slip, or into the notes app on your phone. Stick it inside the medicine cupboard. You'll never regret having it.

A sensible home setup

Keep a box of oral rehydration sachets in the cupboard — they're cheap, widely available and far better than water alone when you're losing salts. Keep a thermometer. Keep a note of your regular medicines and doses somewhere a family member could find it.

And if you're caring for someone else, remember that a febrile, dehydrated older person can become confused quickly. That's a same-day call, not a wait-and-see.

Safety rails worth saying out loud

• Never stop or change a regular medicine on your own. Not for a day, not 'just while I'm ill'.
• Read the leaflet, but don't treat it as a personal plan — it's written for everyone, not for you.
• Get advice early. A quick phone call to your pharmacy is free, and pharmacists are used to these questions.
• Call 111 if you're unsure, and 999 for chest pain, severe breathlessness, confusion, a fit, or being unable to pass urine at all.

A winter bug is unpleasant enough without an avoidable medicine problem layered on top. Ten minutes with your pharmacist this week could save you a very long night in January.