Metformin is normally well tolerated, although as with all drugs, unwanted adverse effects sometimes occur. The most common adverse effects are gastrointestinal disturbances, generally lasting only for the first few days of treatment. This can usually be avoided by starting with a low dose and by taking metformin with meal. Very rarely, lactic acidosis has been associated with Metformin treatment. Virtually all reported cases, however, have involved patients with contraindications to treatment or in acute overdose. It is therefore important that the contraindications are strictly adhered to. Other common adverse effect is taste disturbance and very rarely, decrease of Vit. B12 absorption with decrease of serum levels during long-term use of metformin, hepatitis and skin reactions (i.e., erythema, pruritus, urticaria).