How Do Antidiarrheals Work?


Antidiarrheals are a class of medications used to treat acute and chronic diarrhea. Antidiarrheals help to reduce the frequency and urgency of passing stools; however, they do not eliminate the cause of diarrhea, and hence, diarrhea will occur as soon as you stop the antidiarrheal medications until the underlying cause (such as infection or inflammation) is treated properly.

Diarrhea is a common problem and usually lasts for a couple of days, whether treatment is taken or not; however, antidiarrheals will help you feel better, especially if you have cramping pains. It can be caused by:

  • Bacteria and parasites
  • Viruses
  • Medications such as antibiotics
  • Lactose intolerance (inability to digest lactose, the main carbohydrate in dairy)
  • Food allergies
  • Digestive disorders (irritable bowel syndrome, celiac disease, Crohn’s disease)

Antidiarrheals are administered through oral and intravenous routes; a few are also available as over-the-counter medicines without a prescription from your doctor. Do not take antidiarrheal agents without the prescription of a healthcare professional when diarrhea is accompanied by fever, severe illness, or abdominal pain or if there is blood or pus (mucus) in the stools.

Antidiarrheals work in the following ways:

  • Antidiarrheals work by decreasing the flow of fluids and electrolytes into the bowel and slowing down the movement of the bowel to decrease the number of bowel movements.
  • This allows more fluid to be absorbed into your body which helps in having less diarrhea and more formed and bulky stools.
  • They help in balancing the way fluid moves through your intestines and thus reduce inflammation. 
  • They also slow the growth of bacteria that might cause diarrhea.


Diarrhea can lead to a serious loss of body water (dehydration) and minerals (electrolytes). Drink plenty of fluids to replace the nutrients you may have lost. In addition, stick to a bland diet during this time to reduce the irritation to your stomach/intestines. Antidiarrheals can be used in conditions such as:

  • Acute/chronic diarrhea
  • Gas, upset stomach, heartburn, indigestion, nausea, flatulence
  • Traveler"s diarrhea (an intestinal infection that occurs as a result of eating or drinking contaminated food or water)
  • Irritable bowel syndrome (a chronic disorder that causes abdominal pain, bloating, and alternating diarrhea and constipation)
  • Severe diarrhea associated with metastatic carcinoid tumors (a type of slow-growing cancer that can arise in several places throughout your body)
  • AIDS-related diarrhea
  • Chemotherapy-related diarrhea 
  • Short bowel syndrome (a malabsorption disorder caused by a lack of functional small intestine)
  • Post ileostomy (a surgical operation in which a damaged part is removed from the ileum and the cut end diverted to an artificial opening in the abdominal wall)
  • Stomach ulcers caused by Helicobacter pylori


Consult your doctor if you develop signs of dehydration (e.g., extreme thirst, decreased urination, muscle cramps, weakness, and fainting).

Common side effects include:

  • Constipation
  • Fatigue
  • Drowsiness
  • Dizziness (feeling faint, weak, or unsteady)
  • Dry mouth
  • Loss of appetite
  • Abdominal pain
  • Nausea and vomiting
  • Other rare side effects include:
  • Severe constipation/nausea/vomiting
  • Fast/irregular heartbeat
  • Fainting
  • Tinnitus (ringing, whistling, or other sounds in the ears)
  • Black stools/tongue

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.


Drug names include:                              


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