Lotronex treats irritable bowel syndrome (IBS) in women whose main problem is diarrhea. May cause constipation. Tell your doctor if you are taking other medications to treat diarrhea.

Lotronex Overview


Lotronex is a prescription medication used to treat women with the symptoms of severe irritable bowel syndrome (IBS) including diarrhea, pain, cramps, and the urgent need to have bowel movements. Lotronex belongs to a group of drugs called serotonin agonists which work by slowing the movement of stool through the intestines.

This medication comes in tablet form and is usually taken twice daily, with or without food.

Common side effects of Lotronex  include constipation and nausea.

Patient Ratings for Lotronex

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  • Other
  • Abdominal Pain
  • Diarrhea
  • Irritable Bowel Syndrome

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  • A month or so
  • A few months
  • A year or so
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Lotronex Cautionary Labels


Uses of Lotronex

Lotronex is a prescription medicine only for some women with severe chronic IBS whose main problem is diarrhea and IBS symptoms have not been helped enough by other treatments.

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.


Lotronex Drug Class

Lotronex is part of the drug class:

Side Effects of Lotronex

Some patients have developed serious bowel side effects while taking Lotronex. Serious bowel (intestine) side effects can happen suddenly, including the following.

Serious complications of constipation: About 1 out of every 1,000 women who take Lotronex may get serious complications of constipation. These complications may lead to a hospital stay and, in rare cases, blood transfusions, surgery, and death. People who are older, who are weak from illness, or who take other constipating medicines may be more likely to have serious complications of constipation with Lotronex.
To lower your chances of getting serious complications of constipation, do the following:

  • If you are constipated, do not start taking Lotronex.
  • If you get constipated while taking Lotronex, stop taking it right away and call your doctor.
  • If your constipation does not get better after stopping Lotronex, call your doctor again.
  • If you stopped taking Lotronex, do not start taking Lotronex again unless your doctor tells you to do so.

Ischemic colitis (reduced blood flow to the bowel): About 3 out of every 1,000 women who take Lotronex over a 6-month period may get a serious problem where blood flow to parts of the large bowel is reduced. This is called ischemic colitis. The chance of getting ischemic colitis when you take Lotronex for more than 6 months is not known. Ischemic colitis may lead to a hospital stay and, in rare cases, blood transfusions, surgery, and death.
To lower your chances of getting serious complications of ischemic colitis, stop taking Lotronex and call your doctor right away if you get:

  • new or worse pain in your stomach area (abdomen) or
  • blood in your bowel movements.

Constipation is the most common side effect among women with IBS who take Lotronex. 

Lotronex Interactions

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Lotronex and other medicines may affect each other. Always check with your doctor before starting or stopping any medicines. Especially tell your doctor if you take:

  • antihistamines
  • certain antidepressants ('mood elevators') called tricyclic antidepressants
  • certain medications to treat asthma, diarrhea, lung disease, mental illness, motion sickness, overactive bladder, pain, Parkinson's disease, stomach or intestinal cramps, ulcers and upset stomach

Also, be sure to mention to your doctor if you take:

  • amiodarone (Cordarone, Pacerone)
  • certain antifungals such as fluconazole (Diflucan), itraconazole (Sporanox), ketoconazole (Nizoral), and voriconazole (Vfend)
  • aprepitant (Emend)
  • cimetidine (Tagamet)
  • clarithromycin (Biaxin, in Prevpac)
  • cyclosporine (Neoral, Sandimmune)
  • diltiazem (Cardizem, Dilacor, Tiazac, others)
  • erythromycin (E.E.S., E-Mycin, Erythrocin)
  • fluoroquinolone antibiotics including ciprofloxacin (Cipro), gatifloxacin (Tequin), levofloxacin (Levaquin), norfloxacin (Noroxin), ofloxacin (Floxin), others
  • fluoxetine (Prozac, Sarafem)
  • hormonal contraceptives (birth control pills, implants, injections, rings, and patches)
  • hydralazine (Apresoline)
  • isoniazid (INH, Nydrazid)
  • lovastatin (Advicor, Altocor, Mevacor)
  • certain medications for human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS) such as atazanavir (Reyataz), delavirdine (Rescriptor); efavirenz (Sustiva);indinavir (Crixivan), lopinavir (in Kaletra), nelfinavir (Viracept), ritonavir (Norvir, in Kaletra), and saquinavir (Fortovase, Invirase)
  • nefazodone
  • procainamide (Procanbid, Pronestyl)
  • sertraline (Zoloft)
  • telithromycin (Ketek)
  • ticlopidine (Ticlid)
  • troleandomycin (TAO)
  • verapamil (Calan, Covera, Isoptin, Verelan)
  • zafirlukast (Accolate)

Lotronex Precautions

Lotronex may cause serious gastrointestinal (GI; affecting the stomach or intestines) side effects including ischemic colitis (decreased blood flow to the bowels) and severe constipation that may need to be treated in a hospital and may rarely cause death.

Tell your doctor if you are taking any of the following medications: antihistamines; certain antidepressants ('mood elevators') called tricyclic antidepressants; or certain medications to treat asthma, diarrhea, lung disease, mental illness, motion sickness, overactive bladder, pain, Parkinson's disease, stomach or intestinal cramps, ulcers and upset stomach.

Tell your doctor if you are constipated now, if you often have constipation, or if you have had problems resulting from constipation.

Also tell your doctor if you have a blockage in your bowels, ischemic colitis, blood clots, or any disease that causes inflammation of the bowels such as Crohn's disease (swelling of the lining of the digestive tract), ulcerative colitis (sores or swelling in the lining of the large intestine), or diverticulitis (small pouches in the lining of the large intestine that can become inflamed).

Stop taking Lotronex and call your doctor right away if you experience any of the following symptoms:

  • Constipation
  • New or worse pain in the abdomen (stomach area)
  • Blood in your bowel movements
  • Call your doctor again if your constipation does not get better after you stop taking Lotronex.
  • Once you have stopped taking Lotronex because of these symptoms, do not start taking it again unless your doctor tells you that you should.

Only certain doctors who are registered with the company that makes Lotronex and who are aware of the possible side effects can write prescriptions for this medication. Your doctor will give you the manufacturer's patient information sheet (Medication Guide) before you begin treatment with Lotronex and your pharmacist will give you a copy each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions. After you read the Medication Guide for the first time, your doctor will ask you to sign an agreement that says that you understand the benefits and risks of taking Lotronex and that you will follow the directions for taking Lotronex safely. If you do not understand or can not follow the directions in the Medication Guide you should not take Lotronex. You also can obtain the Medication Guide from the manufacturer's website.

Talk to your doctor about the risks of taking Lotronex.

Do not take Lotronex if any of the following apply to you:

  • Your main IBS problem is constipation or you are constipated most of the time. 
  • You have had a serious problem from constipation. If you are constipated now, do not start taking Lotronex. 
  • You have had serious bowel blockages. 
  • You have had blood flow problems to your bowels, such as ischemic colitis. 
  • You have had blood clots. 
  • You have had Crohn's disease, ulcerative colitis, diverticulitis, or severe liver disease. 
  • You are taking fluvoxamine (LUVOX).

Lotronex Food Interactions

Grapefruit and grapefruit juice may interact with Lotronex and lead to potentially dangerous effects. Discuss the use of grapefruit products with your doctor.

Inform MD

Talk with your doctor:

  • about the possible benefits and risks of Lotronex. 
  • about how much of a problem IBS is in your life and what treatments you have tried. 
  • about any other illnesses you have and medicines you take or plan to take. These include prescription and non-prescription medicines, supplements, and herbal remedies. Certain illnesses and medicines can increase your chance of getting serious side effects while taking Lotronex. Other medicines may interact with how the body handles Lotronex. 
  • about any allergies that you have.  
  • if you are pregnant, planning to get pregnant, or breastfeeding.

Lotronex and Pregnancy

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

This medication falls into category B. There are no well-done studies that have been done in humans with Lotronex. But in animal studies, pregnant animals were given this medication, and the babies did not show any medical issues related to this medication.

Lotronex and Lactation

Tell your doctor if you are breastfeeding or planning to breastfeed. It is not known if Lotronex is excreted in human breast milk or if it will harm your nursing baby.

Lotronex Usage

  • Take Lotronex exactly as your doctor prescribes it. You can take Lotronex with or without food. 
  • If you miss a dose of Lotronex, just skip that dose. Do not take 2 doses the next time. Wait until the next time you are supposed to take it and then take your normal dose. 
  • If you see other doctors about your IBS or side effects from Lotronex, tell the doctor who prescribed Lotronex.

Lotronex Dosage

Take Lotronex exactly as precribed by your doctor. Follow the directions on your prescription label carefully. Your doctor will determine the best dose for you.

The recommended dosage is:

  • Begin with 0.5 mg two times a day for 4 weeks to see how Lotronex affects you. You and your doctor may decide that you should keep taking this dose if you are doing well. 
  • Check with your doctor 4 weeks after starting Lotronex:
    • If you try 0.5 mg two times a day for 4 weeks, it may not control your symptoms. If you do not get constipation or other side effects from Lotronex, your doctor may increase your dose up to 1 mg two times a day. 
    • If 1 mg two times a day does not work after 4 weeks, Lotronex  is not likely to help you. You should stop taking it and call your doctor. 

Lotronex Overdose

If you take too much Lotronex, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away.

Other Requirements

  • Store Lotronex  between 59ºF to 86ºF (15ºC to 30ºC).
  • Protect Lotronex from light and getting wet (moisture).
  • Keep Lotronex and all medicines out of the reach of children.

Lotronex FDA Warning


Infrequent but serious gastrointestinal adverse reactions have been reported with the use of this medication. These events, including ischemic colitis and serious complications of constipation, have resulted in hospitalization and, rarely, blood transfusion, surgery, and death.

The Prescribing Program for Lotronex was implemented to help reduce risks or serious gastrointestinal adverse reactions. Only prescribers who have enrolled in the Prometheus Prescribing Program for Lotronex should prescribe this medication.

This medication is indicated only for women with severe diarrhea-predominant irritable bowel syndrome (IBS) who have not responded adequately to conventional therapy. Before receiving the initial prescription for this medication, the patient must read and sign the Patient Acknowledgement Form for Lotronex.

Discontinue this medication immediately in patients who develop constipation or symptoms of ischemic colitis. Do not resume this medication in patients who develop ischemic colitis. Patients should immediately report constipation or symptoms of ischemic colitis to their prescriber. Patients who have constipation should immediately contact their prescriber if the constipation does not resolve after this medication is discontinued. Patients with resolved constipation should resume this medication only on the advice of their treating prescriber.