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Systematic (IUPAC) name
Clinical data
Pronunciation /lˈpɛrəmd/
Trade names Imodium, others[1]
AHFS/Drugs.com monograph
MedlinePlus a682280
  • AU: B3
  • US: C (Risk not ruled out)
Legal status
Routes of
Pharmacokinetic data
Bioavailability 0.3%
Protein binding 97%
Metabolism Liver (extensive)
Biological half-life 9-14 hours[2]
Excretion Faeces (30-40%), urine (1%)
CAS Number 53179-11-6 YesY
Template:CAS (with HCl)
ATC code A07DA03 (WHO)
A07DA05 (oxide)
PubChem CID: 3955
DrugBank DB00836 N
ChemSpider 3818 YesY
KEGG D08144 YesY
Synonyms R-18553
Chemical data
Formula C29H33ClN2O2
Molecular mass 477.037 g/mol (513.506 with HCl)
 NYesY (what is this?)  (verify)

Loperamide, sold under the brand name Imodium among others,[1] is a medication used to decrease the frequency of diarrhea.[2] It is often used for this purpose in gastroenteritis, inflammatory bowel disease, and short bowel syndrome. It is not recommended for those with blood in the stool. The medication is taken by mouth.[2]

Common side effects include abdominal pain, constipation, sleepiness, vomiting, and a dry mouth. It may increase the risk of toxic megacolon.[2] Loperamide's safety in pregnancy is unclear, but there is no evidence of harm.[3] It appears to be safe in breastfeeding.[4] It is an opioid that is not absorbed.[5] It works by slowing the contractions of the intestines.[2]

Loperamide was first made in 1969 and used medically in 1976.[6] It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.[7] It is sold as a generic medication and is not very expensive.[2][8] Wholesale the cost is about 0.004 to 0.04 USD a dose.[9] In the United States it is about 0.20 USD a dose.[2]

Medical uses

Loperamide is effective for the treatment of a number of types of diarrhea.[10] This includes control of acute nonspecific diarrhea, mild traveler's diarrhea, irritable bowel syndrome, chronic diarrhea due to bowel resection, and chronic diarrhea secondary to inflammatory bowel disease. It is also useful for reducing ileostomy output. Off-label uses for loperamide also include chemotherapy induced diarrhea, especially related to irinotecan use.

Loperamide should not be used as the primary treatment in cases of bloody diarrhea, acute exacerbation of ulcerative colitis, or bacterial enterocolitis.[11]

Loperamide is often compared to diphenoxylate. Recent studies suggest that loperamide is more effective and has lower neural side effects.[12][13][14]

Side effects

Treatment should be avoided in the presence of high fever or if the stool is bloody (dysentery). Treatment is not recommended for patients that could suffer detrimental effects from rebound constipation. If there is a suspicion of diarrhea associated with organisms that can penetrate the intestinal walls, such as E. coli O157:H7 or salmonella, loperamide is contraindicated as a primary treatment.[11] Loperamide treatment is not used in symptomatic C. difficile infections, as it increases the risk of toxin retention and precipitation of toxic megacolon.

Loperamide should be administered with caution to patients suffering from hepatic impairment due to reduced first pass metabolism.[15] Additionally, caution should be used when treating patients with advanced HIV as there have been cases of both viral and bacterial toxic megacolon. If abdominal distension is noted, therapy with loperamide should be discontinued.[16]

The use of loperamide in children under 2 years is not recommended. There have been rare reports of fatal paralytic ileus associated with abdominal distention. Most of these reports occurred in the setting of acute dysentery, overdose, and with very young children less than two years of age.[17] A systematic review and meta-analysis examined control trials of loperamide in children under 12 years old, and found that serious adverse events occurred only in children under 3 years old. The study reported that the use of loperamide should be contraindicated in children under 3 years old, systemically ill, malnourished, moderately dehydrated, or have bloody diarrhea.[18] In 1990, all pediatric formulations of the antidiarrheal loperamide were banned in Pakistan.[19]

Loperamide is not recommended in the UK for use during pregnancy nor by nursing mothers.[20] In the US, loperamide is classified by the FDA as pregnancy category C. Studies in rat models have shown no teratogenicity, but there have not been sufficient studies in humans.[21] One controlled, prospective study of 89 women exposed to loperamide during the first trimester showed no increased risk of malformations. This, however, was only one study with a small sample size.[22] Loperamide can be present in breast milk, and is not recommended for breast feeding mothers.[16]

Adverse drug reactions (ADRs) most commonly associated with loperamide are constipation (which occurs in 1.7%-5.3% of users), dizziness (up to 1.4%), nausea (0.7%-3.2%), and abdominal cramps (0.5%-3.0%).[23] Rare, but more serious, side-effects include: toxic megacolon, paralytic ileus, angioedema, anaphylaxis/allergic reactions, toxic epidermal necrolysis, Stevens-Johnson syndrome, erythema multiforme, urinary retention, and heat stroke.[24] The most frequent symptoms of loperamide overdose are drowsiness, vomiting and abdominal pain or burning.[25]

Drug interactions

Loperamide is a substrate of P-glycoprotein, therefore the concentration of Loperamide will increase when given with a P-Glycoprotein inhibitor.[23] Common P-Glycoprotein inhibitors include quinidine, ritonavir, and ketoconazole, among others.[26] Loperamide is also capable of decreasing the concentration of other P-Glycoprotein substrates. As an example, when saquinavir concentrations can decrease by half when given with loperamide.[23]

Loperamide is an anti-diarrheal agent which decreases intestinal movement. As such, when combined with other antimotility drugs, there is an increased risk of constipation. These drugs include, but are not limited to, other opioids, antihistamines, antipsychotics, and anticholinergics.[27]

Mechanism of action

File:Loperamide ball-and-stick.png
Ball-and-stick model of loperamide molecule

Loperamide is an opioid-receptor agonist and acts on the μ-opioid receptors in the myenteric plexus of the large intestine; by itself it does not affect the central nervous system. It works similarly to morphine, by decreasing the activity of the myenteric plexus, which in turn decreases the tone of the longitudinal and circular smooth muscles of the intestinal wall.[28][29] This increases the amount of time substances stay in the intestine, allowing for more water to be absorbed out of the fecal matter. Loperamide also decreases colonic mass movements and suppresses the gastrocolic reflex.[30]

Blood–brain barrier

Loperamide is subject to efflux by P-glycoprotein. This mechanism effectively prevents loperamide from crossing the blood-brain barrier and so shields the CNS from exposure (and thus risk of CNS tolerance/dependence).[31]

Concurrent administration of P-glycoprotein inhibitors such as quinidine could potentially allow loperamide to cross the blood–brain barrier. Quinidine with loperamide was found to produce respiratory depression, indicative of central opioid action.[32]

Loperamide has been shown to cause a mild physical dependence during preclinical studies, specifically in mice, rats, and rhesus monkeys. Symptoms of mild opiate withdrawal were observed following abrupt discontinuation of long-term treatment of animals with loperamide.[33][34]

When originally approved for medical use in the United States, loperamide was considered a narcotic and was put into Schedule II of the Controlled Substances Act 1970. It was transferred to Schedule V on 17 July 1977 and then decontrolled as of 3 November 1982. (source: Federal Register)


Loperamide hydrochloride was first synthesized by Paul Janssen from Janssen Pharmaceutica in Beerse (Belgium), following previous discoveries of diphenoxylate hydrochloride (1956) and fentanyl citrate (1960).[35]

The first clinical on loperamide were published in 1973 in the Journal of Medicinal Chemistry[36] with the inventor being one of the authors.

The trial against placebo was conducted from December 1972 to February 1974, its results being published in 1977 in Gut journal, an edition of British Society of Gastroenterology.[37]

The drug was patented in the USA in 1973.[38][39]

In 1973 Janssen started to promote loperamide under the brand name Imodium.

In December 1976 Imodium got FDA approval.[40]

During the 1980s, Imodium became the best-selling prescription antidiarrheal in the United States.[41]

In March 1988 McNeil Pharmaceutical began selling loperamide as the OTC product under the brand name Imodium A-D.[42]

In the 1980s there also existed loperamide in the form of drops (Imodium Drops) and syrup. Initially it was intended for children's usage, but Johnson & Johnson voluntarily withdrew it from the market in 1990 after 18 cases of paralytic ileus (resulting in 6 deaths) has been registered in Pakistan and reported by World Health Organization.[43] In the following years (1990-1991) products containing loperamide have been restricted for children use in a number of countries (ranging from 2 to 5 years of age).[44]

In the late 1980s prior to the expiration of US patent in January 30, 1990,[41] McNeil company started to develop Imodium Advanced containing loperamide and simethicone for treating both diarrhea and flatulence. In March 1997 the company patented such combination.[45] The drug has been approved in June 1997 by FDA as Imodium Multi-Symptom Relief in the form of a chewable tablet.[46]

In November 1993 loperamide has been launched as an orally disintegrating tablet based on Zydis technology.[47][48] Imodium Instant Melts from Johnson & Johnson is currently the only loperamide available in the form of orally disintegrating tablets.[49][50]

In 2013 loperamide in the form of 2 mg tablets has been added to WHO Model List of Essential Medicines.[51]

Society and culture


It is as a generic medication and is not very expensive.[2][8] Wholesale the cost is about 0.004 to 0.04 USD a dose.[9] In the United States it is about 0.20 USD a dose.[2]

Brand names

Loperamide was originally marketed as Imodium, and there are many generic brands.[1]


  1. 1.0 1.1 1.2 Drugs.com International brands for loperamide Page accessed Sept 4, 2015
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 "Loperamide Hydrochloride". The American Society of Health-System Pharmacists. Retrieved Aug 25, 2015. 
  3. "Prescribing medicines in pregnancy database". Australian Government. 3 March 2014. Retrieved 22 April 2014. 
  4. "Loperamide use while Breastfeeding". Retrieved 26 August 2015. 
  5. "loperamide hydrochloride". NCI Drug Dictionary. Retrieved 26 August 2015. 
  6. Patrick, Graham L. (2013). An introduction to medicinal chemistry (Fifth edition. ed.). Oxford: Oxford University Press. p. 644. ISBN 9780199697397. 
  7. "WHO Model List of Essential Medicines" (PDF). World Health Organization. October 2013. Retrieved 22 April 2014. 
  8. 8.0 8.1 Hamilton, Richard J. (2013). Tarascon pocket pharmacopoeia (14 ed.). [Sudbury, Mass.]: Jones & Bartlett Learning. p. 217. ISBN 9781449673611. 
  9. 9.0 9.1 "Loperamide HCL". International Drug Price Indicator Guide. Retrieved 26 August 2015. 
  10. Hanauer, S. B. (Winter 2008). "The Role of Loperamide in Gastrointestinal Disorders". Reviews in Gastroenterological Disorders. 8 (1): 15–20. PMID 18477966. 
  11. 11.0 11.1 http://www.drugs.com/pro/loperamide.html
  12. Miftahof, Roustem (2009). Mathematical Modeling and Simulation in Enteric Neurobiology. World Scientific. p. 18. ISBN 9789812834812. 
  13. Benson, Al; Chakravarthy, A.; Hamilton, Stanley R.; et al., eds. (2013). Cancers of the Colon and Rectum: A Multidisciplinary Approach to Diagnosis and Management. Demos Medical Publishing. p. 225. ISBN 9781936287581. 
  14. Zuckerman, Jane N. (2012). Principles and Practice of Travel Medicine. John Wiley & Sons. p. 203. ISBN 9781118392089. 
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  19. "E-DRUG: Chlormezanone". Essentialdrugs.org. 
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  21. http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm?fuseaction=Search.Label_ApprovalHistory#labelinfo
  22. Einarson, A.; et al. (2000). "Prospective, controlled, multicentre study of loperamide in pregnancy". Canadian journal of gastroenterology. 14 (3): 185–187. PMID 10758415. 
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  31. Upton, RN (Aug 2007). "Cerebral uptake of drugs in humans.". Clinical and experimental pharmacology & physiology. 34 (8): 695–701. PMID 17600543. doi:10.1111/j.1440-1681.2007.04649.x. 
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External links