Sick Day Rules on a GLP-1

Everyone on this medication should have a sick day plan, and almost nobody is given one. It takes ten minutes to agree and it is the single highest-value conversation in this whole series.

The reason is not that these drugs are dangerous. It is that a perfectly ordinary stomach bug lands on a body already running a lower fluid intake, alongside a medication list assembled when you were well.

Why illness is different on a GLP-1

Three things stack:

You were already running lean on fluid. Thirst cues quieten along with appetite, and roughly a fifth of daily water normally arrives inside food you are no longer eating.

The drug slows gastric emptying, so the vomiting and nausea of a viral illness sit on top of a stomach that was already emptying slowly.

Your other medications assume you are well. A diuretic is correct at 90 kg and eating normally. It is not correct on day two of gastroenteritis.

The outcome that follows is acute kidney injury, which appears in the prescribing information, and it is very largely preventable — the full picture is in GLP-1s and kidney disease.

The hold list

This is the conventional list of medications held during an illness causing vomiting, diarrhea or markedly reduced intake. Yours should be personalised and written down by whoever prescribes them — this is the shape of the conversation, not a substitute for it.

The mnemonic taught in the UK is the “sick day rules” list, and it long predates these drugs. What is new is how many people on a GLP-1 are also on two or three of these, and how much less fluid reserve they are carrying.

Do not stop insulin. People with type 1 diabetes in particular need insulin during illness even when not eating — stopping it is how diabetic ketoacidosis happens. Sulfonylurea and insulin doses may need reducing if you genuinely cannot eat, and that is a same-day phone call rather than a unilateral decision.

The SGLT2 inhibitor problem specifically

This deserves its own section because it is the one people miss.

SGLT2 inhibitors — empagliflozin, dapagliflozin, canagliflozin — can cause euglycemic diabetic ketoacidosis: a genuine ketoacidosis in which the blood glucose reading looks normal or only mildly raised. Illness, low carbohydrate intake and dehydration are the classic triggers, and a GLP-1 supplies the low intake.

Because the glucose reading is reassuring, people and occasionally clinicians are falsely reassured. The symptoms to act on are nausea and vomiting, abdominal pain, and deep or rapid breathing, with a normal glucose. If you take one of these drugs, know this exists, hold it when you are unwell, and say “I take an SGLT2 inhibitor” to anyone assessing you.

What to do, in order

1. Fluid, in small amounts, constantly. 50–100 ml every 10–15 minutes beats a glass every 2 hours. A slow stomach copes badly with volume.

2. Use an oral rehydration formulation with glucose in it. Not a zero-sugar electrolyte. The glucose is not a compromise — sodium-glucose co-transport is the mechanism that pulls water across the gut wall, and it is why the WHO formula is built at roughly 75 mmol/L sodium with 75 mmol/L glucose. Keep sachets in the cupboard before you need them; the reasoning is in the electrolytes rankings.

3. Hold what needs holding, per your agreed list.

4. Keep eating what you can, in small plain amounts, aiming to resume normal intake within 24–48 hours. Resting the bowel has not held up as advice.

5. Pause the extras. Fibre supplements, prebiotics, iron and magnesium can all wait 3–5 days — see the fibre rankings for why bulking agents are the wrong move mid-illness.

6. Decide about the injection. Many prescribers advise holding a weekly dose during significant vomiting. Know that this does not clear the drug — the half-life is about a week, so levels persist regardless, as explained in how long these drugs stay in your system. And know the restart rules, because resuming after a gap sometimes means dropping a dose step, as covered in what to do if you miss a dose.

When to call, and when to go in

Call the same day if:

• You cannot keep any fluid down for 24 hours
• You are passing much less urine than usual, or none
• You feel dizzy or faint on standing
• You take a diuretic, ACE inhibitor, ARB or SGLT2 inhibitor and cannot keep fluids down
• Your glucose is running very high or very low and you take insulin or a sulfonylurea

Go to an emergency department for:

• Confusion or drowsiness
• Blood in vomit or stool
• Severe abdominal pain, particularly upper abdominal pain radiating to the back
• Deep or rapid breathing, especially on an SGLT2 inhibitor
• Chest pain

Tell whoever assesses you, unprompted, that you take a GLP-1 — the same instruction that applies before surgery and procedures, and for the same reason.

The ten-minute conversation to have now

Before you are ill, ask your prescriber four questions and write the answers somewhere you will find them:

1. Which of my medications do I hold if I am vomiting or have diarrhea?
2. Do I hold my GLP-1 dose, and what do I do about restarting?
3. At what point do you want me to call?
4. If I take insulin or a sulfonylurea, what do I do about the dose when I cannot eat?

Put the answers on your phone or on the fridge. The entire value of a sick day plan is that it exists before the day you need it, and nobody makes good decisions about this at 3 a.m. with a bowl beside them.