Important Safety Information: Metformin

Gastrointestinal effects are common, particularly early: nausea, diarrhea, and abdominal discomfort. Long-term use is associated with reduced B12 absorption, which is why B12 is monitored. Lactic acidosis is rare but serious (it carries an FDA boxed warning, the agency's highest-level alert), and risk rises with kidney impairment, significant alcohol use, and certain acute illnesses. Watch for unusual tiredness, muscle pain, trouble breathing, or stomach pain, and seek care if these occur. Kidney function must be assessed before starting and monitored during.