Loperamide

Adults: 4 mg initially, then 2 mg after each loose stool, max 16 mg/day. Avoid in children <12 outside medical supervision.

Constipation, abdominal cramps, dizziness. High-dose abuse can cause serious cardiac arrhythmia.

Bloody diarrhea, dysentery, suspected bacterial infection (typhoid, severe C. difficile), children <2.

Loperamide acts on µ-opioid receptors in the intestinal wall without crossing the blood-brain barrier in normal use, slowing transit and reducing stool volume. Useful for acute non-infectious diarrhea and chronic conditions like IBS-D.