Loperamide hydrochloride is an off the counter medication for treatment of various diarrhea syndromes. By decreasing peristalsis of the intestine, it prolongs the gastrointestinal transit time and increases absorption of fluids and electrolytes from the stool to the gastrointestinal tract.
Loperamide is a synthetic derivative of phenylpiperidine, and is very similar to diphenoxylate, another derivative used to treat diarrhea. It is a strong agonist of micro -opiate receptors found in both the central nervous system and the gastrointestinal tract. Nevertheless, loperamide is considered to be a specific and safe treatment, when administered systemically or orally due to its inability to cross the blood-brain barrier and effect opiatic receptors in the brain.
Besides its effect as an opiate-receptor agonist, loperamide also behaves as a calcium-calmodulin antagonist and was shown to inhibit NMDA receptors, HCN channels, and voltage-gated Ca2+ channels.