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Metformin and diabetes tablets around surgery | CION Cancer Clinics
Metformin is often skipped around the day of cancer surgery, but the plan depends on your kidneys and the operation. Other diabetes medicines are handled differently: some that cause low sugar are skipped on the fasting morning, and SGLT2 tablets such as Jardiance are often stopped earlier. Your anaesthetist and diabetes doctor write the plan. This page explains what they weigh and what to watch for. CION Cancer Clinics’ surgical oncologists in Hyderabad can talk this through with you.
MI
Medically reviewed by Dr. Mohammed ImaduddinConsultant Surgical Oncologist · MBBS, MS (General Surgery), MCh (Surgical Oncology) · last reviewed September 2026, next review due September 2027
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On this page
- Do you have to stop metformin before surgery?
- Which diabetes medicines are handled differently?
- What happens to your sugar and tablets around the operation?
- What do the words about your sugar mean?
- What do families often believe about diabetes tablets and surgery?
- What can this page not tell you?
- Common questions about diabetes tablets and surgery
The short answer
Do you have to stop metformin before surgery?
Often metformin is skipped around the day of surgery, but not always, and some other diabetes tablets need to be stopped earlier. Your anaesthetist, surgeon and diabetes doctor decide which tablets to hold and when. The aim is to keep your sugar steady while you are fasting and recovering, without letting it fall too low or climb too high.
Why diabetes tablets need a plan
You will not eat for a while before the anaesthetic, and you may eat little for some time after. A tablet that lowers sugar can push it too low while you are not eating. Stopping all tablets without a plan can let it rise too high, which slows healing and raises the risk of infection.
Why good control before surgery matters
The team may check your HbA1c, a blood test showing your average sugar over recent months. If it is very high, they may work with your diabetes doctor to improve control before the operation, if the cancer plan allows time. This is about making surgery safer, not about blaming you.
Never stop, skip or change a diabetes medicine because of this page. Ask for a written plan.What you take
Which diabetes medicines are handled differently?
Each group carries its own concern around surgery. Many people take a combination strip that contains two of these, so bring the strip itself.
Metformin
Sold as Glycomet and other names. It rarely causes low sugar alone, but it may be held around surgery, especially if your kidneys are weak or a scan with contrast dye is planned.
Sulphonylureas
Glimepiride (Amaryl) and gliclazide are common. They push the body to release insulin even when you have not eaten, so low sugar on the fasting morning is the main concern.
SGLT2 tablets
Dapagliflozin (Forxiga) and empagliflozin (Jardiance). These can cause a rare but dangerous build-up of acid in the blood around surgery, even when sugar readings look normal. They are often stopped earlier than other tablets.
Gliptins and others
Sitagliptin (Januvia), vildagliptin and teneligliptin rarely cause low sugar. Weekly injections or tablets such as semaglutide slow stomach emptying, which matters for the anaesthetic.
Tell the team about
- Any weekly injection
- Insulin, even if only at night
Not sure whether this applies to you?
Ask an oncologist
!
One thing that cannot wait
If you take Forxiga, Jardiance or a similar tablet and develop vomiting, belly pain, fast or deep breathing, unusual sleepiness or confusion before or after surgery, go to the nearest emergency department at once. This can happen even when your sugar reading is normal. Say that you take this diabetes tablet and have had or are due for surgery. Do not wait to see if it passes.
Step by step
What happens to your sugar and tablets around the operation?
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The pre-anaesthesia check
Bring every diabetes strip, pen and your recent sugar diary. The anaesthetist reviews your HbA1c and kidney tests, and writes a plan naming each medicine.
-
The days before
Some tablets, such as SGLT2 tablets, may be stopped first. Others carry on as usual. Check your sugar more often if you have been asked to, and note any low readings.
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The fasting morning
You are usually told which tablets to skip. Check your sugar before leaving home if you have a meter. Bring glucose tablets or a sugary drink in case of a low, and ask in advance whether you may take it.
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During and just after surgery
The team checks your sugar regularly. For longer operations, or when sugar is hard to control, insulin may be given through a drip for a while, even if you never use insulin at home.
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Eating again
Tablets restart once you are eating and drinking normally and the team is satisfied your kidneys are working well. Your discharge summary should say which to restart and when.
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On your report
What do the words about your sugar mean?
- HbA1c
- A blood test showing your average sugar over the past few months, rather than on a single day.
- Hypoglycaemia
- Low blood sugar. Shaking, sweating, confusion or unusual behaviour can be signs. It is the main risk on a fasting morning.
- Ketoacidosis
- A build-up of acid in the blood when the body burns fat for fuel. With SGLT2 tablets it can occur even when sugar readings look normal.
- Insulin infusion
- Insulin given steadily through a drip in hospital, with frequent sugar checks, while you cannot eat.
- eGFR
- A number estimating how well your kidneys filter blood. It affects whether metformin is safe to continue.
Commonly believed
What do families often believe about diabetes tablets and surgery?
"He is not eating, so we will stop all his diabetes medicines."
Stopping everything without a plan can let sugar rise sharply, especially with stress from surgery. Some medicines are held, others continue, and insulin may even be needed. Follow the written plan for each medicine.
"Her sugar reading is normal, so the tablets cannot be causing a problem."
With Forxiga, Jardiance and similar tablets, a serious acid build-up can happen with normal sugar readings. Vomiting, belly pain or fast breathing need urgent attention whatever the meter says.
"Needing insulin in hospital means the diabetes has become worse."
Insulin through a drip is often the simplest way to keep sugar steady while you cannot eat. Most people go back to their usual tablets once eating normally.
"Sweets and sugary drinks are forbidden on the fasting morning."
Rules on clear drinks vary. If your sugar drops low, treating it matters more than the fast. Ask the anaesthetist in advance exactly what you may take for a low, and tell the ward if you needed it.
Being straight with you
What can this page not tell you?
This page cannot tell you which of your own diabetes medicines to hold, or for how long. It does not know your HbA1c, your kidney function, the operation or what else you take. Your anaesthetist and diabetes doctor put those together into a plan.
Who general advice suits least
People on insulin, people with frequent low sugars, people with kidney disease, people on SGLT2 tablets or weekly injections, and people whose sugar is poorly controlled need a plan made specifically for them. Surgery on the stomach, bowel or pancreas can also change how long you go without normal food.
If you are managing a parent's diabetes
Photograph every strip and pen, front and back. Keep the written plan on your phone. Carry the sugar meter to hospital. After discharge, ask which tablets restart and when, and what sugar readings should prompt a call. Appetite is often poor for a while after surgery, and the dose that suited before may not suit now.
Questions we are asked
Common questions about diabetes tablets and surgery
How many days before surgery should metformin be stopped?
There is no single rule. Many people only skip it around the day of the operation, while others hold it longer because of kidney function or a planned contrast scan. Your anaesthetist and surgeon set the timing for you. Follow the date and instructions on your own written plan.
Can I take my diabetes tablet on the morning of surgery?
Often not, because you are fasting and some tablets can push sugar too low. But the answer depends on the tablet. Your plan should name each medicine and say whether to take it that morning. If it does not, ask at the pre-anaesthesia check rather than guessing.
What if my sugar goes low while fasting?
Treat it as your team told you in advance, usually with glucose tablets or a sugary drink, and recheck. Tell the hospital when you arrive what you took and when. A treated low is safer than an untreated one. Ask about this before the day so you are not unsure in the moment.
Why was Jardiance stopped earlier than my other tablets?
SGLT2 tablets such as Jardiance and Forxiga carry a rare risk of acid building up in the blood around surgery and fasting. Stopping them earlier lowers that risk. The exact timing is set by your team. Watch for vomiting, belly pain or fast breathing, and seek urgent help if they appear.
Will my operation be cancelled if my sugar is high?
Sometimes a planned operation is moved so sugar can be brought under better control first, because very high sugar slows healing and raises infection risk. This is weighed against the need to treat the cancer without delay. Your team explains the balance for your situation.
I use insulin at night. Does that change?
Often the dose the night before is adjusted, but this is decided by your anaesthetist or diabetes doctor. Do not change it on your own. Bring your pens and your recent readings to the pre-anaesthesia check so the team can write a clear insulin plan.
I take a weekly diabetes injection. Should I mention it?
Yes, always. Weekly injections such as semaglutide slow how quickly the stomach empties, which can matter for a safe anaesthetic. The anaesthetist may change the plan for fasting or the injection. Tell them the day you last took it.
When do diabetes tablets restart after surgery?
Usually once you are eating and drinking normally and your kidney tests are satisfactory. Metformin in particular waits for kidney function to be confirmed. Make sure the discharge summary lists each medicine, when to restart it, and which sugar readings should prompt a call.
Meet the Specialists
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Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
Surgical Oncologist
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Sources
- NHS — Metformin
- NHS — Dapagliflozin
- NICE — Perioperative care in adults (NG180)
- American Cancer Society — Cancer surgery
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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Diabetic and facing cancer surgery?
Tell us what operation has been advised and bring your sugar reports and medicine strips. We will help you reach a surgical team who can plan it safely.