How is LOTRONEX® taken?

LOTRONEX works differently from other medications, so follow these directions carefully

Unlike other medicines, LOTRONEX works by reducing the effects of having too much serotonin in your gut. For it to be effective, it is recommended that you take it every day—not just when symptoms are bothering you. Other things to remember about taking LOTRONEX:

  • If you stop taking LOTRONEX, your symptoms could return within 1 to 2 weeks. Be sure to take LOTRONEX as directed by your doctor
  • Taking less than your doctor tells you to will not lower the chances of serious side effects. It may even stop LOTRONEX from working as well as it can
  • Talk to your doctor about the right dosage for you and any other questions you may have

LOTRONEX comes in 2 strengths:

  • Begin with 0.5 mg twice 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 take 0.5 mg twice 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 twice a day
    If 1 mg twice a day does not work after 4 weeks, LOTRONEX is not likely to help you. You should stop taking it and call your doctor
  • 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 severe IBS or side effects from LOTRONEX, tell the doctor who prescribed LOTRONEX

If you are constipated, do not take LOTRONEX.

Before using LOTRONEX® for the first time, you should:
  • Understand that LOTRONEX has serious risks for some people.
  • Read and follow the directions in the Medication Guide.

LOTRONEX is a medicine only for some women with severe irritable bowel syndrome (IBS) whose main problem is diarrhea; whose IBS symptoms have lasted 6 months or longer and have not been helped enough by other treatments.

You can tell if your IBS is severe if at least 1 of these is true: you have lots of painful stomach cramps or bloating; you often cannot control the need to have a bowel movement, or you have “accidents” where your underwear gets dirty from diarrhea or bowel movements; you cannot lead a normal home or work life because you need to be near a bathroom.

Enough testing has not been done to confirm if LOTRONEX works in men or children under 18.


LOTRONEX can cause serious side effects:

Some patients have reported serious intestinal side effects while taking LOTRONEX. These include:

  • Serious complications of constipation
  • Reduced blood flow to the bowel (ischemic colitis)

These can happen suddenly and may lead to a hospital stay and, in rare cases, blood transfusions, surgery, and death.

Stop taking LOTRONEX and call your doctor right away if you have problems clearing your bowels (are constipated) or get new or worsening pain in your stomach area or blood in your stools. 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.

People who are older, who are weak from sickness, or who take other constipating medicines may be more likely to have serious complications of constipation with LOTRONEX.

Who should not take LOTRONEX?

Do not take LOTRONEX if any of these apply to you:

  • Your main IBS problem is constipation or you are constipated most of the time.
  • You have had a bad problem from constipation. If you are constipated now, do not start taking LOTRONEX.
  • You have had bad 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, sores in the colon (ulcerative colitis), swelling of a sac in the intestine (diverticulitis), or severe liver disease.
  • You do not understand the Medication Guide or are not willing to follow it.
  • You are taking a medicine called LUVOX® (fluvoxamine).
What are the possible side effects of LOTRONEX?

The most common side effects of LOTRONEX are constipation, stomach pain and nausea. Some patients have developed serious bowel side effects while taking LOTRONEX. These are not all the possible side effects of LOTRONEX. Your doctor or pharmacist can give you a more complete list. Call your doctor for medical advice about side effects.

You are encouraged to report side effects of prescription drugs to the FDA. Visit or call 1-800-FDA-1088.