Side effects

These include:

• diarrhoea, nausea - occasionally accompanied by a metallic taste - these side effects are not uncommon after commencement of metformin therapy - these side effects may resolve with time
• if treatment is started with a small initial dose (e.g. metformin 500mg od) and dosage is increased gradually then gastrointestinal effects are less likely
• there have been malabsorption syndromes reported associated with metformin treatment
• lactic acidosis may occur with metformin use although Salpeter et al concluded that the use of metformin in type 2 diabetes does not increase the risk for fatal or non-fatal lactic acidosis or increase in blood lactate concentrations compared with placebo or other hypoglycaemic treatments (1)

Reference:

1. Salpeter S et al (2002). Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes. Cochrane Database Syst Reve: CD002967 (latest version 27 Feb 2002).
2. Prescribers' Journal (2000), 40 (1), 38-48.