Metformin is a common medicine for type 2 diabetes. It helps lower blood sugar mainly by reducing glucose production by the liver and improving how the body uses insulin.
Quick summary
Metformin is often used early in type 2 diabetes care, but it is not right for everyone. Kidney function, liver disease, heavy alcohol use, heart failure, contrast imaging, pregnancy, side effects, and other medicines can affect safety.
Key takeaways
- Common side effects include nausea, diarrhea, stomach upset, and loss of appetite.
- Taking metformin with food may reduce stomach side effects for some people.
- Kidney function should be checked before and during treatment.
- A rare but serious risk is metformin-associated lactic acidosis.
Safety points to know
The prescribing information includes kidney-function cautions and instructions around some iodinated contrast imaging procedures. People should not stop metformin on their own before a scan; they should follow the imaging center or clinician’s instructions.
Long-term metformin use may be associated with lower vitamin B12 levels in some people. Ask whether B12 testing is appropriate if you have anemia, neuropathy symptoms, or long-term use.
When to call
- Severe vomiting or diarrhea.
- Dehydration or serious illness.
- New trouble breathing, unusual sleepiness, severe weakness, or feeling very unwell.
- Symptoms of low blood sugar if metformin is combined with insulin or medicines that can cause lows.
- Questions before contrast imaging, surgery, or major illness.
Practical takeaway
Metformin is familiar, but familiar does not mean ignore safety. Ask what monitoring you need and what symptoms should prompt a call.
Safety note
This article is not a substitute for medical care. Seek urgent care for severe illness, dehydration, breathing trouble, confusion, or symptoms that feel dangerous.
What to ask your care team
- Is my kidney function safe for metformin?
- What should I do before contrast imaging or surgery?
- Could my stomach symptoms, B12 level, or other medicines affect my metformin plan?
Related reading
Source summary
- Metformin Hydrochloride Tablets Prescribing Information, DailyMed, National Library of Medicine. FDA label repository. Accessed June 5, 2026. Source
- Insulin, Medicines, and Other Diabetes Treatments, National Institute of Diabetes and Digestive and Kidney Diseases. Patient guidance. Accessed June 5, 2026. Source
- About Type 2 Diabetes, Centers for Disease Control and Prevention. Patient guidance. Accessed June 5, 2026. Source
- Managing Diabetes, National Institute of Diabetes and Digestive and Kidney Diseases. Patient guidance. Accessed June 5, 2026. Source