Unlike trials conducted today on new antimicrobials, the introduction of fusidic acid was not accompanied by extensive studies on toxicity and side effects. The early studies on small numbers of patients reported fusidic acid to be a nontoxic drug with the main side effects being gastrointestinal tract discomfort, diarrhoea and headache. Case reports of hepatotoxicity were reported from 1972. A retrospective analysis showed this to be reversible and mainly associated with intravenous administration. Rarely reported side effects are granulocytopenia, thrombocytopenia and venous spasm. Skin reactions, including contact dermatitis, are uncommon. After many years of use the most common side effects reported for fusidic acid are minor and relate to the gastrointestinal tract.