Metformin causes gastrointestinal adverse effects including nausea, vomiting, diarrhoea, abdominal pain and loss of appetite (>10%) are very common: these occur most frequently during initiation of therapy and resolve spontaneously in most cases. To prevent these gastrointestinal symptoms, it is recommended that metformin be taken in 2 or 3 daily doses during or after meals. A slow increase of the dose may also improve gastrointestinal tolerability.
Absorption of various substances including vitamin B12 may be impaired. Patients may experience a metallic taste and there may be weight loss.
Lactic acidosis can occur but is very rare.
Mild erythema has been reported in some hypersensitive individuals. However, the incidence of such effects is regarded as very rare (<0.01%).