Lotronex (Alosetron) – Oral


Lotronex (alosetron) has a boxed warning, the strongest warning required by the Food and Drug Administration (FDA). The warning states that Lotronex has been associated with rare but serious gastrointestinal (GI) reactions. Some of these events have resulted in hospitalizations and, in rare cases, blood transfusion, surgery, and death.

Because of this, Lotronex should only be used in women with severe irritable bowel syndrome with diarrhea (IBS-D) who have tried other medications that have not been effective. People should stop taking Lotronex immediately and contact their healthcare provider if they develop constipation or symptoms of ischemic colitis (blocked blood flow to the colon).

Symptoms of ischemic colitis may include stomach pain, blood in the stools, a feeling of urgency to have a bowel movement, nausea, and/or diarrhea.

Those who develop ischemic colitis from Lotronex should not take Lotronex again at any time. If you develop constipation from Lotronex, consult your healthcare provider for medical advice before restarting Lotronex.

What Is Lotronex?

Lotronex (alosetron) is an oral prescription drug used to treat women with irritable bowel syndrome with diarrhea (IBS-D) who have not responded to other medications. It is available as a tablet that is taken by mouth.

Lotronex is in a drug class called selective serotonin 5-HT 3 antagonists. It works by slowing the movement of stool (bowel movements) through the intestines.

Drug Facts

Generic Name: Alosetron

Brand Name(s): Lotronex

Drug Availability: Prescription

Administration Route: Oral

Therapeutic Classification: Selective serotonin 5-HT 3 antagonist

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Alosetron

Dosage Form(s): Tablet

What Is Lotronex Used For?

The Food and Drug Administration (FDA) approved Lotronex for use in women with severe IBS-D:

  • Who have had IBS symptoms for at least six months
  • With no other abnormalities of the gastrointestinal tract (the digestive tract that runs from the mouth to the anus)
  • Who have not responded to other medications

Lotronex is not approved for use in men.

People with severe IBS-D experience diarrhea and one or more of the following symptoms:

  • Frequent and severe stomach pain
  • Frequent urgency to have a bowel movement or fecal incontinence (inability to control bowel movements)
  • Disability or inability to perform routine daily activities

How to Take Lotronex

If you are prescribed Lotronex, read the prescription label and the information leaflet that comes with your medication. Consult your healthcare provider if you have any questions.

Use Lotronex exactly as directed by your provider. Do not start taking it if you are constipated. If you already take Lotronex and become constipated, stop treatment and call your healthcare provider.

You can take Lotronex with or without food. Lotronex may help with IBS-D symptoms like stomach pain, diarrhea, and the feeling of urgency to have a bowel movement. However, Lotronex does not work for everyone. Call your healthcare provider if your symptoms do not improve in four weeks.

If you stop taking Lotronex, check with your healthcare provider before starting it again. In some cases, it may not be safe to take Lotronex again.


Store Lotronex at room temperature (between 68 and 77 degrees F), away from direct light, heat, and moisture. Keep the bottle tightly closed when not in use. Keep all medications out of reach of children and pets to prevent accidental consumption.

How Long Does Lotronex Take to Work?

You may notice an improvement in symptoms within one or two weeks. Lotronex does not work for everyone. If you do not feel better in four weeks, contact your healthcare provider.

What Are the Side Effects of Lotronex?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a healthcare provider. You may report side effects to the FDA at www.fda.gov/medwatch or 800-FDA-1088.

Like other medications, Lotronex can cause side effects. Tell your healthcare provider about any side effects you experience while taking this medication.

Common Side Effects

The most common side effects of Lotronex are:

  • Bloating
  • Constipation
  • Gas
  • Indigestion
  • Nausea and vomiting
  • Acid reflux
  • Stomach pain and discomfort
  • Upper respiratory infection

Severe Side Effects

Call your healthcare provider immediately if you have serious side effects. Dial 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Constipation: Constipation from Lotronex can occur suddenly and can be serious. Constipation can lead to hospitalization and other complications, including serious illness and death. People at higher risk include older or weakened women or women who take other medicines that affect bowel movements. If you are taking Lotronex and experience constipation, stop taking Lotronex and contact your healthcare provider immediately.
  • Ischemic colitis (lack of blood flow to the colon): This may happen suddenly and without warning. Women with rectal bleeding, bloody diarrhea, or new or worsening stomach pain should get emergency medical help.

Long-Term Side Effects

A clinical trial that looked at the safety of Lotronex concluded that constipation was the most common side effect with long-term treatment. However, constipation did tend to occur in the earlier months of treatment.

A nine-year evaluation concluded that incidences of constipation and ischemic colitis were rare. This lack of adverse side effects is likely due to the Risk Evaluation and Mitigation Strategy (RISK) program, which educates healthcare providers and users about the risks of Lotronex.

If you have any symptoms that may lead to serious complications, such as constipation or bloody stools, call your healthcare provider immediately.

Report Side Effects

Lotronex may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Lotronex Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (tablets):
    • For irritable bowel syndrome (IBS):
      • Adults—At first, 0.5 milligram (mg) twice a day for 4 weeks. Your doctor may increase your dose to 1 mg twice a day for another 4 weeks.
      • Children—Use and dose must be determined by your doctor.


Lotronex is only approved for use in women; it is not approved for use in men. Lotronex is also not approved for use in children due to the risk of serious side effects.

You may need to use caution when taking Lotronex if you are 65 years or older. Older adults are at higher risk for constipation and must be closely monitored during treatment.

People with mild or moderate liver problems must use this medication with caution. People with severe liver problems should not take Lotronex.

Women who are pregnant, planning to become pregnant, or are breastfeeding should consult their healthcare provider about Lotronex use.

Missed Dose

If you miss a dose of Lotronex, skip the missed dose. Take the next dose at the regular time. Do not take two doses to try to make up for a missed dose.

Overdose: What Happens If I Take Too Much Lotronex?

Doses up to eight times higher than the recommended daily dose of Lotronex have been used in studies without significant side effects. That being said, it is still recommended never to take more than the prescribed amount of your medication.

If you do overdose on Lotronex, you may be treated for any symptoms that occur.

What Happens If I Overdose on Lotronex?

If you think you or someone else may have overdosed on Lotronex, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Lotronex, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.

Stop taking alosetron and check with your doctor right away if you become constipated or have symptoms of poor blood flow to your bowels (ischemic colitis). Some symptoms of poor blood flow are: new or worsening abdominal pain, bloody diarrhea, or blood in the stool.

Do not start taking alosetron again unless your doctor tells you to do so.

Do not take this medicine if you are also using fluvoxamine (Luvox®).

What Are Reasons I Shouldn't Take Lotronex?

Lotronex is not appropriate for everyone. You should not take this medication if you are allergic to alosetron or any of the inactive ingredients in Lotronex.

Additionally, you should not take Lotronex if you:

  • Have constipation or a history of chronic or severe constipation
  • Have a history of gastrointestinal blockages, stricture (tightening of the esophagus), perforation (holes), or adhesion (scar tissue)
  • Have a history of ischemic colitis or other problems with circulation in the intestines
  • Have a history of toxic megacolon (a life-threatening complication from colon infection or disease)
  • Have Crohn's disease or ulcerative colitis (UC) or a history of Crohn's disease or UC
  • Have a history of blood clots or clotting problems
  • Have diverticulitis or a history of diverticulitis (inflammation or infection in pouches of the intestine)
  • Have severe liver problems (classified as Child-Pugh Class C)
  • Take the antidepressant medication Luvox (fluvoxamine)

Lotronex may be prescribed with caution in some people only if the healthcare provider determines it is safe. This includes:

  • People with mild or moderate liver problems (classified as Child-Pugh Class A or B)
  • People at risk for constipation
  • People who have recently changed smoking habits (because smoking affects how Lotronex is processed by the body)

What Other Medications Interact With Lotronex?

Tell your healthcare provider about all the medications you take, including prescription and over-the-counter (OTC) drugs, and vitamins or supplements. While taking Lotronex, do not start any new medications without approval from your healthcare provider.

Lotronex interacts with the antidepressant Luvox (fluvoxamine). However, it does not interact with the SSRI (selective serotonin reuptake inhibitors) antidepressant Prozac (fluoxetine) or the benzodiazepine Xanax (alprazolam). This is because Luvox interacts with the way Lotronex is metabolized in the body, causing very high levels of Lotronex, which can increase the risk of dangerous side effects.

For this same reason, quinolone antibiotics such as Cipro (ciprofloxacin) or levofloxacin, as well as the stomach acid reducer Tagamet HB (cimetidine), should not be combined with Lotronex. Although these drugs have not been evaluated in clinical studies with Lotronex, they are expected to act the same way as Luvox and should be avoided.

Other drugs that may interact with Lotronex include:

Other drug interactions may occur with Lotronex. Consult your healthcare provider for a complete list of drug interactions.

What Medications Are Similar?

People with IBS may have IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), or IBS with a combination of constipation and diarrhea. Lotronex is for women who have IBS-D.

Other drugs used in adults with IBS-D include:

The above is a list of drugs also used for IBS-D. It is not a list of drugs recommended to take with Lotronex. Talk to your pharmacist or a healthcare provider if you have questions.

Frequently Asked Questions

  • What is Lotronex used for?

    Lotronex is used to treat adult women who have irritable bowel syndrome with diarrhea who have not responded to other treatments.

  • How does Lotronex work?

    Lotronex slows the movement of stool through the intestines.

  • What drugs interact with Lotronex?

    Lotronex can interact with other medications, including certain antibiotics, antifungals, and drugs used to treat HIV/AIDS. Before starting Lotronex, review your medication list with your healthcare provider.

  • How long does it take for Lotronex to work?

    You may start feeling better within one or two weeks, but if you do not start feeling better by the four-week mark, contact your healthcare provider.

  • What are the side effects of Lotronex?

    Common side effects are stomach-related and may include bloating, constipation, gas, indigestion, nausea, vomiting, acid reflux, and stomach discomfort. If you have constipation, stomach pain, bloody stools, a feeling of urgency to use the bathroom, nausea, or diarrhea, contact your healthcare provider immediately.

  • How do I stop taking Lotronex?

    Your healthcare provider will tell you how long to take Lotronex.

  • What is the Lotronex REMS program?

    Because of the risk of severe side effects, healthcare providers and patients must fulfill specific requirements.

    As part of the Risk Evaluation and Mitigation Strategy (REMS) program, before prescribing Lotronex, the healthcare provider must complete training. When prescribing Lotronex to a patient, the healthcare provider must educate the patient about the drug and its risks. Before taking Lotronex, you will be required to review the LOTRONEX REMS program Patient Acknowledgement Form with the healthcare provider. This will help you understand the risks of Lotronex and when you should contact the healthcare provider for medical help.

How Can I Stay Healthy While Taking Lotronex?

Living with IBS-D can affect your life in a way that most people do not understand. It is important to see a healthcare provider right away who can examine you, do appropriate testing, and get you on your way to feeling better. Not all IBS-D medications work the same for everyone. If you try one and it doesn't work, contact your healthcare provider and see if you might benefit from trying a different treatment.

When going to the bathroom so frequently, you may experience anal irritation. Here are some tips from the International Foundation for Gastrointestinal Disorders:

  • Wipe gently, and avoid toilet paper that has dyes or fragrances.
  • If you can, wash the area with water only, either with a bidet or shower, using the hose attachment to stream water onto the affected area. Shower after you sweat, such as after a workout.
  • Consult your healthcare provider before applying any ointments or creams to the area. Some may worsen symptoms or cause an allergic reaction.
  • Avoid tight clothing, and wear cotton underwear. Use hypoallergenic detergent to wash your clothes.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Karen Berger, PharmD
Karen Berger, PharmD, is a community pharmacist and medical writer/reviewer.