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Sick Day Rules

Patient advice relating to medicinal sick day rules

Taking certain medicines when you are dehydrated or very unwell can result in you developing a more serious illness. This is because they can increase the risk of dehydration and lead to potentially serious side effects. This is known as Medicine Sick Day Rules. 

Patients should consult a GP or Pharmacist for medication advice if they experience any of the following:

  • Vomiting or diarrhoea on more than one occasion
  • Fevers, sweats or shaking/shivering

You may be advised to temporarily pause certain medications during this time, restarting 24-48 hours after you start eating and drinking normally.

Which illnesses cause dehydration?

Dehydration is the loss of fluid from your body. Vomiting, diarrhoea, and fever (high temperature, sweats, shaking) can make you dehydrated. If you are sick once or have diarrhoea once, then you are unlikely to become dehydrated. Having two or more episodes of vomiting or diarrhoea can lead to dehydration: in these cases, you should consider following this advice.

Which medications are affected by sick day rules?

  • ACE inhibitors: names ending in ‘pril’ – examples: lisinopril, perindopril, ramipril. A medicine for high blood pressure and heart conditions. If you are dehydrated, these medicines can stop your kidneys working properly.
  • ARBs: names ending in ‘sartan’ – examples: losartan, candesartan, valsartan. A medicine for high blood pressure and heart conditions. If you are dehydrated, these medicines can stop your kidneys working properly.
  • Diuretics: sometimes called ‘water pills’ – examples: furosemide, bendroflumethiazide, indapamide, spironolactone. Used for excess fluid and high blood pressure. These medicines can make dehydration more likely.
  • NSAIDs: anti-inflammatory pain killers – examples: ibuprofen, naproxen, diclofenac. If you are dehydrated, these medicines can stop your kidneys working properly.
  • Metformin: a medicine for diabetes. Dehydration can make it more likely that you will develop a serious side effect called lactic acidosis.
  • SGLT2 inhibitors: names ending in ‘flozin’ – examples: canagliflozin, dapagliflozin, empagliflozin, ertugliflozin. A medication used in the treatment of Diabetes, Kidney disease or Heart Failure. These medicines can make dehydration more likely and if you have diabetes can cause acid to build up if you are unwell.

More information relating to SGLT2 inhibitors

Where can I find more information?

Page published: 2 February 2026
Last updated: 12 March 2026