Medications
Metformin Before Surgery
Metformin is a common diabetes tablet. The usual approach is simple — but it depends on your kidney function and whether contrast dye is involved.
Quick answer
Why it matters
Metformin itself doesn't cause low blood sugar, so it's less risky around fasting than insulin or some other diabetes drugs.
The main caution is a rare problem called lactic acidosis, which is more likely if your kidneys are stressed — for example by dehydration, low blood pressure, or contrast dye during surgery. Holding metformin on the day of surgery avoids this.
Do not stop without instruction
What to ask your doctor
- When exactly do I hold metformin and when do I restart?
- Is a contrast-dye scan planned with my surgery?
- How will my blood sugar be managed while I'm fasting?
- Do my kidneys change the plan?
Red flags — call your team
Red flags — call your team
- Known kidney disease
- A contrast (dye) scan planned around surgery
- Very high blood sugar or feeling unwell
References
- American Society of Anesthesiologists (ASA) — perioperative medication management. asahq.org
- Perioperative diabetes management guidance (specialty society consensus).
Frequently asked questions
Do I stop metformin before surgery?
Usually you take it as normal until surgery and hold it on the day of surgery, restarting when you're eating and your kidney function is stable.
Why hold metformin for surgery?
To avoid a rare complication (lactic acidosis) if your kidneys are stressed by fasting, low blood pressure, or contrast dye.