How does imodium (loperamide) actually work, anyway? how bad can it be to overdose?

Imodium (loperamide): Imodium anti-diarrheals are actually a drug called loperamide. This drug acts on the walls of the gut inhibiting their movement and increasing the tone in the sphincter muscle of your anus. This causes your feces to stop moving in your gut allowing your body to absorb more of the water. The drug is fairly safe, however large overdosing can cause constipation, paralytic ileus or toxic megacolon.

Severe consequences: Loperamide is an anti-diarrheal. The way it works is slowing the muscle contractions in your gut, allowing water to escape and your stool to harden. Don’t take any more than 4 mg for the first loose stool and 2 mg for each loose stool afterward, 16 mg/day max (even that dose is high). The consequences of overdose are severe: they can be life-threatening or lead to surgical removal of your bowel.