Alosetron (Oral)

By blocking the action of serotonin, (a chemical found in the intestines) alosetron reduces abdominal discomfort, the urgency of bowel movements, and diarrhea caused by IBS.


Alosetron is used to treat cramps, abdominal pain, urgency of bowel movements, and diarrhea as the main symptom in women with severe, chronic IBS. The medication has not been found to be effective in men with the same condition. Alosetron does not cure irritable bowel syndrome, and may not be of help to every patient who takes it. Patients who stop taking the medication may have their symptoms returning within a week.

Alosetron should only be used by women who have not had much success with other treatments for their IBS condition. IBS is said to be caused by serotonin, a chemical that causes the intestines to become overactive. Alosetron works by blocking the action of serotonin, thereby reducing the cramping, abdominal discomfort, sudden need for bowel movements and diarrhea that are all caused by IBS. Because of the serious side effects of this drug in some patients, a prescription for alosetron can only be written by physicians enrolled in the prescribing program.

Conditions treated

Type of medicine

  • 5-ht3 antagonist

Side Effects

Alosetron has been reported to cause serious side effects on the gastrointestinal tract (stomach and intestines) of some patients. These include severe constipation and schemic colitis, a condition characterized by decreased blood flow to the bowels. These side effects have led hospitalization and even death in some rare cases. It is for this reason that the medication is available only through a restricted marketing program.

With that said, the patient should keep in mind that their doctor prescribes this medication after they have judged that the benefits of taking it are greater than the risks of its side effects. Many people who use alosetron do not experience serious side effects. The patient should stop taking the medication and seek medical attention immediately if any of these side effects occur:

  • Bloody diarrhea or stools
  • Constipation
  • Abdominal/stomach pain (new or getting worse)

Some of the side effects of alosetron may not require medical attention. Patients should ask for advice from their doctor on the various ways to reduce or prevent these side effects. They should be sure check with their doctor if the side effects below persist, or if they need further clarification about them:

  • Feeling full/bloated
  • Bleeding after bowel movement
  • Distention of abdominal/stomach area
  • Pressure in the stomach
  • Swelling around rectal area

Taking alosetron may increase serotonin in the GI tract, and on rare occasions, cause a serious condition known as serotonin syndrome. The risk goes up if the patient is also taking other medications that increase serotonin. It is therefore important that the patient informs her doctor or pharmacist about all the drugs they are taking.
Patients should get emergency medical help if they notice any of the following symptoms: hallucinations, seizures, severe dizziness, rapid heartbeat, unexplained fever, severe nausea, vomiting and diarrhea, twitching muscles, restlessness, and irritability.

Strong allergic reactions to this drug are rare. However, the patient should seek emergency medical help if they notice any of these symptoms of an allergic reaction: swelling, itching, rash, dizziness and difficulty with breathing.

Other side effects not listed here may also occur in some patients. Patients are advised to check with their doctor as soon as possible if any other side effects are experienced.


Alosetron should only be used for treating severe IBS in women, when the main symptom has been diarrhea for at least 6 months. The medication should only be prescribed to women who have tried other treatments for their IBS without much success. Due to the potential severe side effects of this drug, it should not be given to children.
Patients are advised to take their medication exactly as their doctor prescribed. It's also important that they read the prescription label carefully and follow all the directions given. Patients must not alter doses by taking either larger or smaller quantities, or by using the medicine beyond the prescribed duration.

The amount of medication needed will depend on the potency of the medicine. In addition, the number of doses per day, the intervals allowed between those doses, and the duration of treatment all depend on what medical condition the patient is using the medicine for.

Alosetron is available in tablet form to take by mouth. The initial dosage is usually 0.5 mg orally, twice a day. This may be increased to up to 1 mg, twice a day, after four weeks of treatment. Patients should be sure to take the medication at about the same times every day. The dosing information provided here, however, should not be taken as a substitute for medical advice from a doctor. Patients should be sure to get the right prescription for their unique needs from their pharmacist or doctor.

Because of the serious side effects that have occurred in some adults, this medication should not be given to children.

Missed dose:

If the patient misses a dose, they should take it as soon they remember. However they should return to the regular schedule if it's almost time for the next scheduled dose. Patients are strongly advised against double dosing.


It is vital that emergency medical attention is sought immediately an overdose is suspected. The patient should call his or her nearest poison control center immediately. The national poison hotline for US residents is. 1-800-222-1222. Residents in Canada can call their local poison center directly.

Major Drug Interactions

Drug interactions may affect the efficacy of a medication, or increase the risk of serious side effects occurring. For this reason, some medications should not be used together, but there may be instances where the healthcare professional prescribes them together even if an interaction is likely. In such cases, the pharmacist/doctor may alter the dosage, or advise certain precautions.

When taking alosetron, it's important for the patient to tell their doctor if they are also taking any of the drugs listed below. The interactions given here have been chosen on the basis of their significance. The list may not be all inclusive.

It is not recommended to use alosetron with any of these drugs except under special circumstances as determined by the healthcare professional. The doctor may decide not to treat you this medication or they may alter the dosing for the other drugs you are taking:

  • Apomorphine
  • Fluvoxamine

Using alosetron with any of the medicines highlighted below is usually not advised, but may be necessary in some cases. If the pharmacist or doctor prescribes both medicines together, they may decide to change the dose or the frequency of using one or both of the medications:

  • Cimetidine
  • Norfloxacin
  • Ciprofloxacin
  • Gatifloxacin
  • Ofloxacin

The use of alosetron with any of the following could increase the risk of experiencing certain side effects, but the combination may be the best treatment for the patient. If the pharmacist or doctor prescribes both medicines together, they may decide to change the dose or the frequency of using one or both of the medications:

  • Ketoconazole

Other interactions:

To lower the risk of unpleasant interactions from occurring, when taking certain medications it may be necessary to avoid certain foods or beverages. Taking tobacco or alcohol with certain medicines may also trigger interactions. The patient should have a discussion with their doctor about the use of their medicine with food, tobacco and alcohol.

The presence of certain other medical conditions could affect the use of this medicine. Patients should inform their healthcare professional if they suffer from other medical problems, especially:

  • History of severe constipation
  • Blood clotting problems
  • IBS (e.g., ulcerative colitis, Crohn's disease), Intestinal adhesion or stricture (bowel blockage)
  • History of poor intestinal blood circulation or intestinal obstruction
  • Holes in bowel (intestinal perforation)
  • Ischemic colitis (decrease blood flow to bowel)
  • Severe liver problems
  • Mild or moderate liver problems must be used with caution; may increase risk of severe side effects
  • History of toxic mega-colon (enlarged bowel), patients with these condition should not use the medication


Before taking alosetron, the patient should tell her doctor know if they are allergic to the medication or any other drugs. They should also not fail to mention what other prescription and non-prescription drugs they are using or plan to use. Additionally, they must let the doctor know about other herbal products, nutritional supplements or vitamins they are using.

It is very important that the patient pays their doctor regular visits to have their progress check. This allows the doctor to assess whether the medication is effective, and to determine whether or not you should continue using it.

The patient should stop taking alosetron immediately and check with their doctor if they develop constipation or notice symptoms of ischemic colitis (poor blood flow to bowels). Some symptoms of ischemic colitis are: blood in the stool/bloody diarrhea, new worsening stomach/abdominal discomfort. Unless instructed by the doctor, the patient should not start taking alosetron again.

Elderly patients may be more sensitive to this medication's side effects, particularly constipation.

If the patient is pregnant or planning to get pregnant soon, they should be sure to inform their doctor. The doctor will then weigh the risks against the benefits of taking the medicine while pregnant and offer some advice. It is not yet known if this medication is passed through breast milk. Nursing mothers should weigh the potential benefits against the risks of using the medication while breastfeeding.


This medication should be kept tightly closed in its original container, out of the reach of children and pets. Alosetron tablets should be stored at room temperature and away from light, excess heat and moisture (not in the bathroom). It is important to store all medication out of the sight and reach of children, as children can open the containers easily when they find them.

When the doctor determines that treatment with this medication is no longer necessary, any unused tablets must be disposed of properly to ensure that children, pets or other people cannot use them. The patient should talk to her pharmacist about the proper disposal of any left-over medication.


Alosetron tablets are prescribed only to women to treat severe IBS, where the main symptom is diarrhea. The medication is usually not prescribed until other treatments for IBS fail to work for the patient. It is however not a cure for irritable bowel syndrome, and the patient may have a re-occurrence of the symptoms within a week after they stop using the drug.

It is very important for the patient to tell their doctor about other prescription and non-prescription medications, supplements and herbal treatments they may be using at the time. This is so the doctor can determine the safety of taking this medication. Additionally the patient should talk to their doctor about other medical conditions they may be suffering from at the time of treatment. The presence of certain health conditions, particularly those to do with the gastrointestinal tract and the liver, may inhibit the functioning of this drug or increase the risk of side effect.

Due to the risk of very serious or fatal side effects, such as severe constipation and schemic colitis, (decreased flow of blood to the bowels) the distribution of this medication is tightly regulated. Only doctors enrolled in the prescribing program for this drug are allowed to prescribe it. The severity of the side effects also means that the medication should not be given to children. Patients must also take extra care when storing or disposing of this drug to prevent other people, children or pets from using it.

Last Reviewed:
December 10, 2017
Last Updated:
April 26, 2018