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Last reviewed on RxList: 4/11/2019
Lotronex Side Effects Center

Last reviewed on RxList 4/11/2019

Lotronex (alosetron hydrochloride) blocks the action of a chemical called serotonin in the intestines, slowing the movement of stools (bowel movements) through the intestines and is used to treat severe, chronic irritable bowel syndrome (IBS) in women who have had diarrhea as the main symptom for at least 6 months, and should be used only in women who have tried other IBS treatments without success. Lotronex has not been shown to be effective in men with IBS. Common side effects of Lotronex include:

  • headache
  • stomach upset or discomfort
  • hemorrhoids
  • bloating
  • gas
  • nausea
  • constipation
  • burping with heartburn
  • or skin rash

To lower the risk of constipation, Lotronex should be started at a dosage of 0.5 mg twice a day. If, after 4 weeks, the dosage is well tolerated but does not adequately control IBS symptoms, then it may be increased to up to 1 mg twice a day. Lotronex may interact with fluvoxamine, cimetidine, ketoconazole, itraconazole, voriconazole, isoniazid, hydralazine, procainamide, clarithromycin, telithromycin, HIV medicines, nelfinavir, or antibiotics. Tell your doctor all medications and supplements you use. Lotronex should be used only when prescribed during pregnancy. It is unknown if this drug passes into breast milk. Consult your doctor before breastfeeding.

Our Lotronex (alosetron hydrochloride) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Lotronex Consumer Information

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Serious or fatal side effects on the stomach and intestines have occurred in some people taking alosetron. In rare cases, alosetron has caused severe constipation, or ischemic colitis (caused by reduced blood flow to the intestines).

Stop taking alosetron and call your doctor right away if you develop:

  • new or worsening constipation;
  • stomach pain;
  • bright or dark red blood in your stools; or
  • bloody diarrhea.

You may need to permanently discontinue alosetron if you have these side effects.

Older adults and those who are ill or debilitated may be more likely to have serious complications from constipation.

Common side effects may include:

  • constipation;
  • nausea; or
  • pain or discomfort in your stomach or intestines.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Lotronex (Alosetron Hydrochloride)

Lotronex Professional Information


The following adverse reactions are described in more detail in other sections of the label:

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Patients With Irritable Bowel Syndrome

Table 1 summarizes adverse reactions from 22 repeat-dose studies in patients with IBS who were treated with 1 mg of LOTRONEX twice daily for 8 to 24 weeks. The adverse reactions in Table 1 were reported in 1% or more of patients who received LOTRONEX and occurred more frequently on LOTRONEX than on placebo. A statistically significant difference was observed for constipation in patients treated with LOTRONEX compared to placebo (p<0.0001).

Table 1. Adverse Reactions Reported in ≥1% of Patients with Irritable Bowel Syndrome and More Frequently on LOTRONEX 1 mg Twice Daily Than Placebo

Body System
Adverse Reaction
(n = 2,363)
LOTRONEX 1 mg twice daily
(n = 8,328)
Constipation 6% 29%
Abdominal discomfort and pain 4% 7%
Nausea 5% 6%
Gastrointestinal discomfort and pain 3% 5%
Abdominal distention 1% 2%
Regurgitation and reflux 2% 2%
Hemorrhoids 1% 2%


Constipation is a frequent and dose-related side effect of treatment with LOTRONEX [see WARNINGS AND PRECAUTIONS]. In clinical studies constipation was reported in approximately 29% of patients with IBS treated with LOTRONEX 1 mg twice daily (n = 9,316). This effect was statistically significant compared to placebo (p<0.0001). Eleven percent (11%) of patients treated with LOTRONEX 1 mg twice daily withdrew from the studies due to constipation. Although the number of patients with IBS treated with LOTRONEX 0.5 mg twice daily is relatively small (n = 243), only 11% of those patients reported constipation and 4% withdrew from clinical studies due to constipation. Among the patients treated with LOTRONEX 1 mg twice daily who reported constipation, 75% reported a single episode and most reports of constipation (70%) occurred during the first month of treatment, with the median time to first report of constipation onset of 8 days. Occurrences of constipation in clinical trials were generally mild to moderate in intensity, transient in nature, and resolved either spontaneously with continued treatment or with an interruption of treatment. However, serious complications of constipation have been reported in clinical studies and in postmarketing experience [see BOX WARNING and WARNINGS AND PRECAUTIONS]. In Studies 1 and 2, 9% of patients treated with LOTRONEX reported constipation and 4 consecutive days with no bowel movement [see Clinical Studies]. Following interruption of treatment, 78% of the affected patients resumed bowel movements within a 2-day period and were able to re-initiate treatment with LOTRONEX.


A similar incidence in elevation of ALT (>2-fold) was seen in patients receiving LOTRONEX or placebo (1.0% vs. 1.2%). A single case of hepatitis (elevated ALT, AST, alkaline phosphatase, and bilirubin) without jaundice in a patient receiving LOTRONEX was reported in a 12-week study. A causal association with LOTRONEX has not been established.

Long-Term Safety

Patient experience in controlled clinical trials is insufficient to estimate the incidence of ischemic colitis in patients taking LOTRONEX for longer than 6 months.

Women With Severe Diarrhea-Predominant Irritable Bowel Syndrome

Table 2 summarizes the gastrointestinal adverse reactions from 1 repeat-dose study in female patients with severe diarrhea-predominant IBS who were treated for 12 weeks. The adverse reactions in Table 2 were reported in 3% or more of patients who received LOTRONEX and occurred more frequently with LOTRONEX than with placebo. Other events reported in 3% or more of patients who received LOTRONEX and occurring more frequently with LOTRONEX than with placebo included upper respiratory tract infection, viral gastroenteritis, muscle spasms, headaches, and fatigue.

Table 2. Gastrointestinal Adverse Reactions Reported in ≥3% of Women with Severe Diarrhea-Predominant Irritable Bowel Syndrome and More Frequently on LOTRONEX Than Placebo

Adverse Reaction Placebo
(n = 176)
0.5 mg once daily
(n = 175)
1 mg once daily
(n = 172)
1 mg twice daily
(n = 176)
Constipation 5% 9% 16% 19%
Abdominal pain 3% 5% 6% 7%
Diarrhea 2% 3% 2% 2%
Hemorrhoidal hemorrhage 2% 3% 2% 2%
Flatulence 2% 2% 1% 3%
Hemorrhoids 2% 1% 1% 3%
Abdominal pain upper 1% 3% 1% 1%

Adverse reactions reported in another study of 701 women with severe diarrhea-predominant IBS were similar to those shown in Table 2. Gastrointestinal adverse reactions reported in 3% or more of patients who received LOTRONEX and occurring more frequently with LOTRONEX than with placebo included constipation (14% and 10% of patients taking LOTRONEX 1 mg twice daily or 0.5 mg as needed, respectively, compared with 2% taking placebo), abdominal pain, nausea, vomiting, and flatulence. Other events reported in 3% or more of patients who received LOTRONEX and occurring more frequently with LOTRONEX than with placebo included nasopharyngitis, sinusitis, upper respiratory tract infection, urinary tract infection, viral gastroenteritis, and cough.


Constipation was the most frequent adverse reaction among women with severe diarrhea-predominant IBS represented in Table 2. There was a dose response in the groups treated with LOTRONEX in the number of patients withdrawn due to constipation (2% on placebo, 5% on 0.5 mg once daily, 8% on 1 mg once daily, and 11% on 1 mg twice daily). Among these patients with severe diarrhea-predominant IBS treated with LOTRONEX who reported constipation most (75%) reported one episode which occurred within the first 15 days of treatment and persisted for 4 to 5 days.

Other Events Observed During Clinical Evaluation Of Lotronex

During its assessment in clinical trials, multiple and single doses of LOTRONEX were administered, resulting in 11,874 subject exposures in 86 completed clinical studies. The conditions, dosages, and duration of exposure to LOTRONEX varied between trials, and the studies included healthy male and female volunteers as well as male and female patients with IBS and other indications.

In the listing that follows, reported adverse reactions were classified using a standardized coding dictionary. Only those events that an investigator believed were possibly related to LOTRONEX, occurred in at least 2 patients, and occurred at a greater frequency during treatment with LOTRONEX than during placebo administration are presented. Serious adverse reactions occurring in at least 1 patient for whom an investigator believed there was reasonable possibility that the event was related to treatment with LOTRONEX and occurring at a greater frequency in patients treated with LOTRONEX than placebo-treated patients are also presented.

In the following listing, events are categorized by body system. Within each body system, events are presented in descending order of frequency. The following definitions are used: infrequent adverse reactions are those occurring on one or more occasion in 1/100 to 1/1,000 patients; rare adverse reactions are those occurring on one or more occasion in fewer than 1/1,000 patients.

Although the events reported occurred during treatment with LOTRONEX, they were not necessarily caused by it.

Blood and Lymphatic: Rare: Quantitative red cell or hemoglobin defects, and hemorrhage.

Cardiovascular: Infrequent: Tachyarrhythmias. Rare: Arrhythmias, increased blood pressure, and extrasystoles.

Drug Interaction, Overdose, and Trauma: Rare: Contusions and hematomas.

Ear, Nose, and Throat: Rare: Ear, nose, and throat infections; viral ear, nose, and throat infections; and laryngitis.

Endocrine and Metabolic: Rare: Disorders of calcium and phosphate metabolism, hyperglycemia, hypothalamus/pituitary hypofunction, hypoglycemia, and fluid disturbances.

Eye: Rare: Light sensitivity of eyes.

Gastrointestinal: Infrequent: Hyposalivation, dyspeptic symptoms, gastrointestinal spasms, ischemic colitis [see WARNINGS AND PRECAUTIONS], and gastrointestinal lesions. Rare: Abnormal tenderness, colitis, gastrointestinal signs and symptoms, proctitis, diverticulitis, positive fecal occult blood, hyperacidity, decreased gastrointestinal motility and ileus, gastrointestinal obstructions, oral symptoms, gastrointestinal intussusception, gastritis, gastroduodenitis, gastroenteritis, and ulcerative colitis.

Hepatobiliary Tract and Pancreas: Rare: Abnormal bilirubin levels and cholecystitis.

Lower Respiratory: Infrequent: Breathing disorders.

Musculoskeletal: Rare: Muscle pain; muscle stiffness, tightness and rigidity; and bone and skeletal pain.

Neurological: Infrequent: Hypnagogic effects. Rare: Memory effects, tremors, dreams, cognitive function disorders, disturbances of sense of taste, disorders of equilibrium, confusion, sedation, and hypoesthesia.

Non-Site Specific: Infrequent: Malaise and fatigue, cramps, pain, temperature regulation disturbances. Rare: Burning sensations, hot and cold sensations, cold sensations, and fungal infections.

Psychiatry: Infrequent: Anxiety. Rare: Depressive moods.

Reproduction: Rare: Sexual function disorders, female reproductive tract bleeding and hemorrhage, reproductive infections, and fungal reproductive infections.

Skin: Infrequent: Sweating and urticaria. Rare: Hair loss and alopecia; acne and folliculitis; disorders of sweat and sebum; allergic skin reaction; eczema; skin infections; dermatitis and dermatosis; and nail disorders.

Urology: Infrequent: Urinary frequency. Rare: Bladder inflammation; polyuria and diuresis; and urinary tract hemorrhage.

Postmarketing Experience

In addition to events reported in clinical trials, the following events have been identified during use of LOTRONEX in clinical practice. Because they were reported voluntarily from a population of unknown size, estimates of frequency cannot be made. These events have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to LOTRONEX.

Gastrointestinal: Impaction, perforation, ulceration, small bowel mesenteric ischemia.

Neurological: Headache. Skin: Rash.

Read the entire FDA prescribing information for Lotronex (Alosetron Hydrochloride)

Related Resources for Lotronex

Read the Lotronex User Reviews »

© Lotronex Patient Information is supplied by Cerner Multum, Inc. and Lotronex Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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