Metformin is one of the safest, most trusted diabetes medicines we have. We have decades of experience with it, and that is why it is still a first-line treatment for type 2 diabetes in many people.[1,3]
Most side effects people hear about are not dangerous, they are mainly stomach-related:
Loose stools, gas, nausea, abdominal discomfort. These often settle if you start low, take it with meals, or use an extended-release form.
Two important safety points to know.
Vitamin B12 can fall in long-term use.
This can worsen tiredness or nerve symptoms in some people. Your doctor may check B12, Especially if you have numbness, anemia, or long duration of metformin use. [2,4]
Lactic acidosis is very rare, but we avoid metformin in high-risk situations.
Metformin is contraindicated in severe kidney failure (eGFR below 30). It may be temporarily stopped around contrast scans or during severe illness, dehydration, low oxygen states, or major surgery.[2,4]
About the “cancer” fear. There is no good evidence that metformin causes cancer. In fact, many studies suggest metformin use is linked with a lower cancer risk, though this does not mean it is a cancer medicine.[3]
So the right approach is simple. Take metformin as prescribed, report side effects early, and let your doctor decide if any dose change or monitoring is needed.
