Metformin
Metformin is a biguanide. It lowers the amount of glucose the liver releases and helps muscle and fat tissue respond to insulin again, without forcing the pancreas to produce more of it. It is the first-line drug for type 2 diabetes and is also used where insulin resistance and body weight are part of the same problem.
It is taken with food, which blunts the nausea, loose stools and stomach ache that are common in the first weeks and usually settle. The kidneys clear it, so creatinine and eGFR are followed, it is paused around imaging with contrast dye, and alcohol is avoided; these warnings share a single reason, the rare risk of lactic acidosis. Long use lowers vitamin B12 and folate, which is why B12 and homocysteine sit next to HbA1c and glucose on the monitoring list. Levofloxacin can unsettle blood sugar in either direction, and bisoprolol can hide the tremor and pounding heart that normally announce a low.
Deep or rapid breathing, unusual drowsiness, severe muscle aching, or vomiting with cold clammy skin are the signs of lactic acidosis and need urgent medical help. Numbness or pins and needles in the hands and feet on long treatment, or stomach upset that never settles, are reasons to see a doctor.
Reference information, not medical advice. Discuss any change with your doctor.