The commonest adverse effects occurring with mefenamic acid are gastro-intestinal disturbances including diarrhoea. Peptic ulceration and gastro-intestinal bleeding have also been reported. Headache, drowsiness and dizziness have been reported. There may be hypersensitivity reactions including skin rashes and urticaria, and occasionally allergic glomerulonephritis; asthma may be precipitated. Reported haematological effects include haemolytic anaemia, agranulocytosis, pancytopenia and thrombocytopenia. Renal failure, glomerulonephritis and papillary necrosis have been reported.
Therapy should be discontinued if diarrhoea or skin rash occur.
Bronchospasm may be precipitated in patients suffering from, or with a previous history of, bronchial asthma or allergic disease.