**1. Introduction**

Diarrhea is one of the most common symptoms in the gastroenterologist clinical practice. It is defined as an increase in the average number of bowel movements, stool output and/or weight, or a reduced stool consistency, and according to duration, can be acute if it lasts less than 7 days, persistent acute (>7 days and < 14 days), sub-acute (>14 days and < 28 days), or chronic (>4 weeks) [1–6]. Most episodes of acute diarrhea occur as a result of infectious agents or dietary transgression. Acute persistent and subacute diarrhea may be caused by unidentified microorganisms or might be secondary to medications [1]. Chronic diarrhea is one of those conditions with the broadest differential diagnosis, that includes anatomical and/or physiologic abnormalities of the gastrointestinal (GI) tract, inflammatory or neoplastic conditions, malabsorptive disorders, drug side effects, dysbiosis, functional as well as postinfectious syndromes such as small intestine bowel overgrowth (SIBO), functional diarrhea or post-infectious irritable bowel syndrome (Pi-IBS) [2–6]. One of the most common, albeit rarely unconsidered causes, is drug-side effect [7, 8]. A large number of at least 700 drugs have been implicated as cause of chronic diarrhea through a number of different, and sometimes overlapped pathophysiologic mechanisms [9]. Although initial therapy is drug withdrawal, in several cases treatment directed at pathophysiologic mechanism is needed to revert damage and improve symptoms.
