Spironolactone is a potassium-sparing diuretic marketed since the 1960s that is known to cause the same adverse effects as other diuretics as well as some effects of its own, such as hyperkalaemia, gynaecomastia and menstrual disturbances. A cohort study and 2 case-control studies concurred to show an approximately twofold, dose-dependent increase in the incidence of upper gastrointestinal bleeding in patients receiving spironolactone. The postulated mechanism is that spironolactone's aldosterone antagonist activity delays gastroduodenal healing. However, gastrointestinal bleeding is not a common adverse effect of aldosterone antagonists. In practice, although these studies have a low level of evidence, the role of spironolactone should be suspected in the event of a gastrointestinal bleed and caution should be exercised with spironolactone in patients who have predisposing factors to gastrointestinal bleeding.