Can you eat or drink before a CT scan?

There is no single rule for every CT scan. The NHS explains that the hospital where you are having the scan will tell you if there is anything you need to do beforehand. That might be following a special diet, taking certain medicines, not eating or drinking for several hours, or leaving off metal items such as jewellery and clothes with zips.

If your letter or text message gives instructions, follow them exactly, even if a friend or a different scan needed something else. If it says nothing about food or drink, Cambridge University Hospitals states that you are not required to do anything before your scan and may eat and drink as normal.

If you cannot find instructions, or you have diabetes, take medicines at set times or find fasting difficult, contact the department named on your letter before the day rather than guessing.

Cancer Research UK explains that for most scans you have a drink or an injection of contrast medium, or both, which is a dye that shows body tissues more clearly. When contrast is injected, some people feel hot and flushed, notice a metal taste or feel as if they are passing urine. The NHS says these feelings usually pass quickly.

Leeds Teaching Hospitals notes that eating shortly before a contrast injection can sometimes make you feel queasy. A period without food is one way of reducing that.

Cancer Research UK says you may be asked to stop eating and drinking for 2 to 4 hours before a scan if you are having contrast, and to let the team know if not eating is a problem for you. Hospitals set their own times, so a different figure on your letter is not a mistake.

Some preparation involves drinking rather than avoiding drinks. Cambridge University Hospitals describes scans that need oral preparation, either a contrast drink or water, and says you may be asked to arrive up to an hour before the scan to drink an oral contrast that highlights the bowel, sipping each cup slowly over 30 minutes.

Where its letter asks for water preparation, the same trust says you may drink water, cordial, tea and coffee with milk and sugar before the scan, but not eat for 4 hours and not chew gum or drink fizzy drinks for 4 hours. Another hospital might phrase things differently, so use the wording on your own paperwork.

Cancer Research UK says that for a CT scan of the abdomen you might need to drink a liquid contrast medium some time before the scan, drink more liquid contrast or water in the department, or stop eating or drinking a few hours beforehand.

The examples below come from the sources cited. They show the range of what you might be asked to do, not what you will be asked.

Leeds Teaching Hospitals says there is no need to stop taking any medication before the scan. The NHS nevertheless asks you to tell the hospital if you take any medicines, are pregnant or might be pregnant, are breastfeeding, have asthma, kidney or thyroid problems or diabetes, or have had an allergic reaction to contrast dye.

If you have diabetes and are asked to fast, ask the department how to manage your medicines and meals before the day. Do not change insulin or tablets on your own. Cancer Research UK also mentions that a blood test may be used to check that your kidneys are working well before contrast, as there is a small risk that contrast medium can affect the kidneys.

The NHS says that if you were given contrast medium you may be asked to wait in the hospital for up to 30 minutes to make sure you do not have a reaction. Cambridge University Hospitals says you may eat and drink as normal afterwards and should keep drinking plenty of fluids for the rest of the day, especially if you were given a contrast injection.

Tell the radiographer if you feel unwell after the scan. The NHS describes an allergic reaction to contrast as rare but able to cause weakness, sweating and difficulty breathing.