Picture of Loperamide molecule


Chemical Name:
Primary Uses:
Anti-diarrhea, opiate withdrawal comfort medicine (off-label)
Brand Names:
Imodium AD, Kaopectate II, Maalox Anti-Diarrheal

General Information

Loperamide was discovered by Janssen Pharmaceutica in 1969. It is an extremely effective drug against diarrhea resulting from gastroenteritis and inflammatory bowel disease, as well as acute nonspecific diarrhea. Loperamide is available over-the-counter, with the most famous preparation being Imodium AD, now a common household name. There is some evidence that the drug may also be beneficial to withdrawaling opioid addicts for relief from some opiate withdrawal symptoms.1

Pharmacology & Pharmacokinetics

Loperamide is indicated for the control and symptomatic relief of diarrhea, and chronic diarrhea associated with inflammatory bowel disease. Loperamide works by reducing bowel motility, lessening the loss of electrolytes and fluids, and increasing fecal volume, viscosity and bulk density. The desired effect, which is in essence constipation, has not been observed to be affected by tolerance. Loperamide attaches to mu-opioid receptors in the myenteric plexus large intestines, which is where the motility of the smooth muscles on the intestinal wall is decreased, causing the desired effect. It also works as a non-selective calcium channel blocker. Loperamide does not affect the central nervous system like other opioids do, due to its inability to readily cross the blood-brain barrier. The half-life of loperamide ranges from 9.1 to 14.4 hours, with an average of 10.8 hours.2

Legal Status

When loperamide was first introduced in the United States, it was classified as a Schedule V substance due to the presence of a physical withdrawal syndrome. The physical withdrawal syndrome was observed in patients at the end of a long-term clinical study which used very high doses of loperamide; however, loperamide was quickly unscheduled and made available as an over-the-counter drug due to the very, very low abuse potential.

In the United States, this drug is available over-the-counter, and does not require a prescription from a licensed physician. There are no or limited restrictions on age and quantity. Law may differ from state-to-state.

Side Effects

Opiate-like effects have been observed in children under three. It is believed that young children are more sensitive to these effects than adults. Extra care must be exercised in young children and people with a compromised blood brain barrier.3

  • Abdominal pain or discomfort
  • Drowsiness
  • Dizziness
  • Tiredness
  • Dry mouth
  • Nausea and vomiting
  • Skin rash
  • Constipation


Loperamide may cause physical dependence, though it is highly unlikely unless high doses are being used over a long period of time. Clinical trials have indicated it can cause a physical withdrawal syndrome, which briefly resulted in the scheduling of loperamide. The results were insignificant in the end due to the extremely low abuse potential caused by loperamide's inability to cross the blood-brain barrier.


[1] Loperamide. Wikipedia, the free encyclopedia. 1 June 2007. Accessed: June 5, 2007. Last Accessed: February 19, 2009.
[2] Showing Loperamide (DB00836). DrugBank. Accession Number: APRD00275. 1 February 2007. Accessed: June 5, 2007. Last Accessed: February 19, 2009.
[3] Pharmaceutical Information - IMODIUM. RxMed. Accessed: June 5, 2007. Last Accessed: February 19, 2009.