Surreptitious abuse of magnesium laxatives as a cause of chronic diarrhoea.

Surreptitious laxative abuse is increasingly considered as a possible cause of unexplained chronic diarrhoea. Laboratory services for detection of colonic stimulant laxatives are widely available; however, laboratory facilities for identifying patients with magnesium-induced diarrhoea are not commonly provided, making diagnosis difficult. We describe three patients who surreptitiously abused magnesium laxatives, and whose diagnoses were delayed, leading in each case to extensive investigations and lengthy in-patient stays. In all three cases, the diagnosis was eventually made by the simple measurement of magnesium in a random faecal sample. We would like to increase the awareness of surreptitious magnesium laxative abuse as a cause of chronic diarrhoea so that costly and unnecessary investigations may be minimized.