The most frequent adverse effects of metformin are gastrointestinal. They are dose related, tend to occur at the onset of therapy, and are often transient.
Common (1/100 ≤ ADR < 1/10): Gastrointestinal: Anorexia, nausea, vomiting, diarrhoea, epigastric fullness, constipation, heartburn.
Dermatologic: Rash, urticaria, photosensitivity.
Metabolic: Decrease vitamin B12 levels.
Less Common (1/1,000 ≤ ADR < 1/100): Hematologic:Blood dyscrasias, aplastic anemia, hemolytic anemia, bone marrow suppression, thrombocytopenia, agranulocytosis.