Contrast scan safety
Metformin and Contrast Scans: — What Is the Rule?
If you take a medicine for diabetes and you are having a scan with contrast, there is a safety question your team needs to answer before you go in. For many patients no pause is needed. For some, a short pause is advised. Your team makes that call — not you.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026
- Not always needed — Many patients who take diabetes medicine do not need to pause it at all before a contrast scan.
- Kidneys are the deciding factor — Your team checks how your kidneys are working before deciding whether any precaution is needed.
- A short pause, not a long one — When a pause is advised, it covers a limited window around the scan — your team gives the exact timing.
- Always confirm before you go — Do not make this decision yourself. Tell the team what you take and let them advise you.
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Whether you need to pause your diabetes medicine before a contrast scan depends on your kidney function. For many patients, no pause is needed. When a pause is advised, it covers a limited period around the scan. Your oncologist or radiologist decides — confirm this at your pre-scan appointment, not on the day.
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Why does a diabetes medicine matter for a contrast scan?
Contrast dye passes through your kidneys. In a small number of people, contrast can temporarily reduce how well the kidneys work.
Certain blood sugar medicines are also processed by the kidneys. If the kidneys slow down suddenly, the medicine can build up to levels higher than intended.
At high levels, that build-up can — very rarely — cause a serious reaction. This is why your team asks about diabetes medicines before any contrast scan, even when your kidneys appear to be working normally.
Before your contrast scan: what to do
- Tell your team you take a medicine for diabetesDo this when you book the scan, not on the day. It gives them time to check your kidney results and advise you clearly.
- Ask whether a pause is needed for your specific medicineYour team will review your kidney blood test and give you a clear instruction — pause, or no change needed.
- Get the timing in writingIf a pause is advised, ask for the exact start and restart times in writing. Do not rely on memory.
- Bring a list of all your medicinesInclude tablets, insulin, and herbal medicines. This helps the team give you accurate, complete advice.
- Do not decide on your ownDo not stop or continue the medicine based on what you read online. Your kidney results decide, and only your team has those.
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Who decides whether you pause, and how?
Your oncologist or radiologist decides, based on your kidney function results, the type of contrast being used, and other health factors relevant to you.
Most centres check kidney function with a blood test before planned contrast scans. If your results are recent and already on file, a new test may not be needed.
The answer is individual. Someone taking the same medicine as you may get a different instruction because their kidneys work differently. This is why the decision belongs to your team — not to a general rule you read online.
Did you know?
Current guidance from the American College of Radiology notes that most patients with normal or near-normal kidney function do not need to pause their diabetes medicine before contrast imaging.
Guidance in this area has changed over time. If you were told something different at a previous scan, that is worth raising with your team — the advice may have been updated.
Source: American College of Radiology Manual on Contrast Media
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Common questions
Frequently asked questions
Do I always need to stop my diabetes medicine before a contrast scan?
No. Whether a pause is needed depends on your kidney function. Current guidance from the American College of Radiology has moved away from a blanket stop-for-everyone rule. Many patients with normal or near-normal kidney function do not need to pause at all. Your oncologist or radiologist will review your kidney results and give you a specific instruction. Do not assume you need to stop, and do not assume you do not — ask directly.
How long do I need to stop it for?
If a pause is advised, your team will give you the exact timing — when to stop and when to restart. The duration depends on your kidney results and the scan being done. Ask for the instruction in writing or photograph it on your phone. Do not restart the medicine until your team has confirmed it is safe to do so.
What if I forgot to mention my diabetes medicine before the scan?
Tell the radiographer or nurse before the contrast is given — not afterwards. The team can check your kidney results on the spot and decide whether to proceed. If you remember only after leaving, call the imaging centre the same day. Do not wait for your next scheduled appointment.
Does this rule apply to MRI scans as well as CT scans?
MRI scans use a different type of contrast, and the concern is different from the one that applies to CT contrast. Do not apply CT scan guidance automatically to an MRI appointment. Ask your team separately each time, for each type of scan, whether any change to your diabetes medicine is needed.
Will I need a blood test before my scan?
Possibly, but not always. If your team has a recent kidney function result on file, they may not need a new test. If your kidneys have not been checked recently, or your health has changed, a blood test is likely before the scan goes ahead. Your team will tell you whether one is needed and whether it must be done on a separate day.
Can I take my other medicines on the day of the scan?
Usually yes — the pause question is specific to certain diabetes medicines and the type of contrast used. Your other regular medicines are generally taken as usual on the scan day. Confirm with your team for your specific list when you book, not on the morning of the appointment.
What if my scan is urgent and there is no time to pause first?
For urgent or emergency scans, your team will weigh the benefit of getting the scan against the very low risk and manage accordingly. Urgency does not make the question disappear — it changes how it is handled. Tell the team you take a diabetes medicine even in an urgent situation so they can monitor and advise you correctly afterwards.
When can I restart my medicine after the scan?
Wait for your team to confirm when to restart. Do not resume on your own schedule. If you were not given a clear restart instruction before you left, call the imaging centre or your oncology team before taking the next dose. A brief call is safer than guessing.