How Does Imodium Work: Loperamide Mechanism of Action

Last Updated: July 30, 2021

Authored by Olivier George, Ph.D.

Reviewed by Michael Espelin APRN

Imodium (loperamide) is a medication meant to treat diarrhea; however, thanks to its mechanism of action, loperamide is used for other purposes as well. It’s noteworthy, that if diarrhea lasts more than two weeks, the patients shouldn’t try to alleviate the situation by increasing the dosage as it may lead to Imodium overdose and subsequent side effects.

While many have used it, few know how Imodium works. It is important that users understand the medication’s mechanism of action for implementation of effective and safe pharmacotherapy.

How Does Imodium Work?

What Imodium does is treat the symptoms of diarrhea, specifically sudden (acute) diarrhea, including traveler’s diarrhea. It is not designed to be taken for long periods, though in some cases patients will, of time and it does not treat the underlying causes of sudden bowel disturbances.

How Imodium works is it slows down the movement of the intestines. The result is the person taking the Imodium AD has fewer bowel movements, and less water enters the stool. It is vital that patients stick to the recommended doses unless directed to do otherwise by a doctor. These are 4mg for the first dose, then loperamide hydrochloride 2 mg for each subsequent dose until stopping the medication. Since high doses of loperamide can result in heart problems, as FDA assets. Of course, this does not offer a complete understanding of how loperamide works. For that, the loperamide mechanism of action must be understood.

Imodium Work.

What Is Imodium Mechanism Of Action?

For most patients, understanding how Imodium works to stop diarrhea ends with a general explanation. However, the more informed patients are, the better. Since loperamide binds to opioid receptors, it theoretically could act as an opioid in the body, thus forcing some people to look for Imodium AD alternatives. However, there is a problem with this theory: loperamide does not easily cross the blood-brain barrier (BBB).

Loperamide binds to the opiate receptor in the gut wall and the colon is the main site of Imodium. Consequently, it inhibits the release of acetylcholine (neurotransmitter) and prostaglandins (compounds involved in dealing with injury or damage). When this happens, peristalsis (contraction of muscles) will be reduced and intestinal transit time (the time it takes for food to travel from the mouth to digestive tract to anuse) will be increased. Moreover, Loperamide increases the tone of the anal sphincter (controls the release of stool). When this happens, incontinence and urgency will be reduced.

To truly understand loperamide, people must know the Imodium mechanism of action – or the specific biochemical interaction between the medication and the body. This can be broken down into five aspects of loperamide MOA: pharmacodynamics, absorption, metabolism, protein binding, route of elimination.

Loperamide Pharmacodynamics

Much of what Imodium does comes down to pharmacodynamics. Loperamide, the active ingredient in Imodium, binds to opiate receptors within the gut wall. Through this binding, the release of acetylcholine and prostaglandins is inhibited. This results in reduced propulsive peristalsis, which means it takes longer for the intestines to move waste, increasing the time between bowel movements and allowing the body to absorb more water, creating firmer stool.

Loperamide Absorption

Absorption determines how fast Imodium works. Imodium for diarrhea is primarily absorbed through the stomach, through the intestines can absorb some of the medication. Once it is absorbed, it does not have a significant impact on plasma. Concentrations are the highest between 2.5 hours and 5 hours after taking the medication. The Imodium half-life is approximately 10 hours.

Loperamide Metabolism

Loperamide is metabolized primarily by cytochrome P450 (CYP450) isozymes, CYP2C8 and CYP3A4. These then form N-desmethyl-loperamide, which is the compound that allows Imodium to work. This must be formed for the medication to act on the body. Such metabolism is considered quite safe. In fact, people can take Imodium while breastfeeding, if taken in small amounts.

Loperamide Protein Binding

Loperamide protein binding occurs primarily in the gut wall. The medication almost exclusively binds to the receptors in the longitudinal muscle layer. The plasma protein binding of the medication comes in at 95%, making this the primary site where Imodium does work on the body.

Loperamide Route Of Elimination

Loperamide is primarily excreted through the feces. While some of the medication and its metabolites can be excreted in other manners, the amount is so small as to be considered statistically insignificant.

How Long Does It Take For Imodium To Work?

How long it takes for Imodium to work will depend on what the user is taking it for. How long it takes for Imodium to stop diarrhea is usually somewhere in the range of 24 to 48 hours. However, the medication may start working well before then. For those using it for other purposes, it can range from a few hours to never working at all.

Using Imodium for recreational purposes may cause many adverse side effects and overdose.

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Page Sources

  1. Imodium Capsules Rx. (n.d.) FDA. https://www.accessdata.fda.gov/drugsatfda_docs/label/2016/017694s052lbl.pdf
  2. FDA Drug Safety Communication: FDA Warns About Serious Heart Problems With High Doses of The Anti-diarrheal Medicine Loperamide (Imodium), Including from Abuse and Misuse, (2016), https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-fda-warns-about-serious-heart-problems-high-doses-antidiarrheal
  3. Mellstrand, T. (1987). Loperamide—an opiate receptor agonist with gastrointestinal motility effects. Scandinavian Journal of Gastroenterology, 22(sup130), 65-66. https://www.tandfonline.com/doi/abs/10.3109/00365528709091001
  4. LOPERAMIDE HYDROCHLORIDE​. (2015, November). Retrieved from https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=d358a9c1-47fa-424c-8cc0-24010cfb7ee3&type=display

Published on: May 6th, 2019

Updated on: July 30th, 2021

About Author

Olivier George, Ph.D.

Olivier George is a medical writer and head manager of the rehab center in California. He spends a lot of time in collecting and analyzing the traditional approaches for substance abuse treatment and assessing their efficiency.

Medically Reviewed by

Michael Espelin APRN

8 years of nursing experience in wide variety of behavioral and addition settings that include adult inpatient and outpatient mental health services with substance use disorders, and geriatric long-term care and hospice care.  He has a particular interest in psychopharmacology, nutritional psychiatry, and alternative treatment options involving particular vitamins, dietary supplements, and administering auricular acupuncture.