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 Irritable Bowel Syndrome 
 (IBS)
 กลุ่มอาการลำไส้ไวต่อสิ่งเร้า

 GENERAL CHARACTERISTICS
 SYMPTOMS
 INTESTINAL MOTILITY
 DIAGNOSIS
 
TREATMENT
 SUMMING UP
 CONTROLLING IBS
 
Frequently Asked Questions
 
กลุ่มอาการโรคลำไส้อักเสบ
  INFLAMMATORY 
  BOWEL DISEASE (IBD)
  - Ulcerative colitis
  - Crohn's disease 

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  Irritable Bowel Syndrome (IBS) กลุ่มอาการลำไส้ไวต่อสิ่งเร้า      

 
กลุ่มอาการลำไส้ไวต่อสิ่งเร้า เป็นสาเหตุที่พบได้บ่อยที่สุดของอาการท้องเดินเรื้อรัง พบได้ในคนทุกวัย มักมี
อาการครั้งแรกตั้งแต่เป็นวัยรุ่น ส่วนมากจะเป็น ๆ หาย ๆ หรือเป็นอยู่ประจำนานเป็นแรมปีหรือตลอดชีวิต โดย
ที่สุขภาพทั่วไปแข็งแรงดี และทำงานได้เป็นปกติ เป็นโรคที่ไม่มีอาการแทรกซ้อนที่ร้ายแรงแต่อย่างไร

สาเหตุ
เกิดจากความผิดปกติเกี่ยวกับการทำงานของลำไส้ใหญ่ โดยหาความผิดปกติทางกายภาพ (ร่างกาย) ไม่พบ 
แต่พบว่าโรคนี้ มีความสัมพันธ์กับอารมณ์และจิตใจของผู้ป่วย (เช่น อารมณ์เคร่งเครียด คิดมาก กังวลใจ) ทำ
ให้ลำไส้ใหญ่มีอาการเคลื่อนไหวผิดปกติ จึงเป็นเหตุทำให้ปวดท้อง ท้องเดิน หรือ ไม่ก็ท้องผูก บางคนก็อาจเกิด
จากลำไส้มีความไวต่อการกระตุ้นของอาหารบางชนิด ทำให้ปวดท้อง ท้องเดินง่าย

อาการ
มีอาการถ่ายอุจจาระบ่อยเป็นประจำทุกวัน หรือเป็น ๆ หาย ๆ เรื้อรัง เป็นแรมเดือน แรมปี  ผู้ป่วยมักจะถ่าย
อุจจาระเป็นก้อนเหมือนปกติหลังตื่นนอนตอนเช้าครั้งหนึ่งก่อน แล้วหลังอาหารเช้า จะมีอาการปวดบิดในท้อง
ทันที ต้องเข้าส้วมถ่ายอีก ซึ่งมักจะถ่ายเหลว ๆ หรือเป็นน้ำ และอาจจะถ่ายเหลวอีกหลายครั้งโดยเฉพาะในเวลา
หลังอาหารแต่ละมื้อ บางครั้งอาจมีมูกปน แต่ไม่มีเลือดหรือหนอง  ผู้ป่วยมักมีอาการปวดบิด ๆ ในบริเวณ
ท้องน้อยด้านซ้ายซึ่งเกิดจากการบีบตัวของลำไส้ใหญ่ พอถ่ายอุจจาระแล้วจะหายปวด  ปกติเมื่อเข้านอนแล้ว 
ผู้ป่วยมักจะไม่ต้องลุกขึ้นถ่ายจนกระทั่งรุ่งเช้า

บางคนอาจมีอาการท้องเดินเวลาที่อารมณ์เครียด หรือกังวลใจ เช่น เวลาสอบ เวลาเดินทาง หรือตื่นเต้นตกใจ
บางคนอาจมีอาการท้องเดินหลังกินอาหารเผ็ดจัด มันจัด กะทิ นมสด น้ำส้มสายชู หรือเวลาดื่มชา กาแฟหรือ
เหล้า เบียร์ เป็นต้น
บางคนเมื่อท้องเดินระยะหนึ่งแล้ว จะมีอาการท้องผูก อุจจาระแข็ง และมีขนาดเล็กกว่าปกติ
ผู้ป่วยบางคนอาจมีอาการของโรคกังวล  เช่น อ่อนเพลีย ซึมเศร้า คิดมาก ใจสั่น นอนไม่หลับร่วมด้วย แต่จะไม่มี
อาการน้ำหนักลด และยังทำงานหรือเรียนหนังสือได้เป็นปกติ

สิ่งตรวจพบ
การตรวจร่างกายจะไม่พบสิ่งผิดปกติ

การรักษา
1. แนะนำให้ผู้ป่วยออกกำลังเป็นประจำ ฝึกสมาธิ หรือหาทางผ่อนคลายความเครียดด้วยวิธีต่าง ๆ, หลีกเลี่ยง
    อาหารเผ็ดจัด หรือรสจัด หรืออาหารที่กระตุ้นอาการ, งดดื่มเหล้า ชา หรือกาแฟ, ดื่มน้ำมาก ๆ, กินอาหาร
    ที่มีกาก (เช่นผัก ผลไม้) ให้มาก ๆ, กินสารเพิ่มกากใย  ทุกวัน สิ่งเหล่านี้มักจะช่วยให้อาการดีขึ้น
2. ถ้ามีอาการปวดท้องและถ่ายบ่อยจนเสียงาน ให้กินยาแก้ท้องเดิน เช่น โลเพอราไมด์  หรือ 
    แอนติสปาสโมดิก กินก่อนอาหาร 30-60 นาที หรือเวลามีอาการ   ถ้ามีอาการไม่มากหรือพอทนได้ ก็ไม่
    ต้องกินยาเหล่านี้
3. ถ้ามีอาการท้องผูก ให้ยาระบาย 
4. ถ้ามีอาการคิดมาก กังวลใจ นอนไม่หลับ ให้ยากล่อมประสาท เช่น ไดอะซีแพม (ย17.1) หรือยาแก้ซึมเศร้า 
    เช่น อะมิทริปไทลีน 
5. ถ้ามีอาการเบื่ออาหาร น้ำหนักลด ถ่ายเป็นเลือด หรือต้องลุกขึ้นถ่ายตอนดึกหลังนอนหลับ หรือเริ่มเป็นครั้ง
    แรก เมื่อมีอายุ 40 ปีขึ้นไป หรือสงสัยจะเกิดจากสาเหตุอื่น ควรแนะนำไปตรวจที่โรงพยาบาล อาจต้อง
  
ตรวจอุจจาระ ตรวจเลือด เอกซเรย์ หรือใช้เครื่องมือ "ซิกมอยโดสโคป (Sigmoidoscope)" ส่องตรวจ
    ทวารหนัก เพื่อหาสาเหตุทางร่างกาย ถ้าตรวจไม่พบความผิดปกติ ก็แสดงว่ามีสาเหตุจากกลุ่มอาการนี้ 

ข้อแนะนำ
1. โรคนี้ถือเป็นภาวะเบี่ยงเบนจากคนปกติทั่วไป จะเป็น ๆ หาย ๆ อยู่จนตลอดชีวิต แต่ไม่มีอันตรายใด ๆ 
    ทั้งสิ้น
2. ผู้ที่มีอาการนี้ต้องสังเกตว่า มีความไวต่ออาหารชนิดใด แล้วหลีกเลี่ยงเสีย อาการก็จะทุเลาได้

รายละเอียด
ถ้ามีอาการท้องเดินเรื้อรัง ควรตรวจสาเหตุ

 

GENERAL CHARACTERISTICS
Irritable bowel syndrome, a condition marked by diarrhea, constipation and abdominal pain, is caused by excessive spasms of the large intestine. (It is also known as spastic colon, nervous bowel, irritable colon and mucous colitis.) Irritable bowel syndrome is not considered a disease as such because there are no organic abnormalities or physical changes. In many people, however, stress or feelings of anxiety, guilt or resentment seem to trigger the symptoms, It is probably the most common abdominal complaint brought to the attention of doctors, affecting one-third to one-half of all patients who seek relief from gastrointestinal problems. In addition, many people have irritable bowel syndrome without ever consulting their doctors about it.

 

The condition appears in late adolescence or early adulthood. For unknown reasons, women are affected about twice as often as men.

 

SYMPTOMS
The abdominal discomfort of an irritable bowel ranges from sharp, cramping-like pains to a continuous, dull ache. It is often relieved by a bowel movement. The lower left part of the abdomen may be tender to the touch. This abdominal pain usually appears after eating, although no particular food or type of food can be identified as the cause.

 

There is also usually diarrhea, sometimes alternating with constipation. The diarrhea typically occurs immediately after a meal or when getting up in the morning, and there is often mucus in the stool. In addition, there may be other, less definite symptoms, such as fatigue, anxiety and difficulty in concentrating.

 

These symptoms may last for a few days or weeks and then cease for months at a time. Also, they may recur with varying degrees of intensity, over a long period.

 

INTESTINAL MOTILITY
After nutrients have been digested and absorbed in the small intestine, the waste material is propelled into the large intestine (also called the colon or bowel) for eventual elimination as a bowel movement. Under normal circumstances, regular muscular contractions (intestinal motility) move this waste matter along the five-foot length of the colon and into the rectum. When the irritable bowel syndrome is present, however, the pattern of motility becomes disordered by excessive muscular contractions, which cause the pain, diarrhea and constipation.

 

It is not known what causes the overactivity of the intestinal muscle. Emotional stress is believed to be a factor in a great many cases. Some researchers think that the syndrome is an allergic response to particular foods. There also is some evidence that alcohol, caffeine and heavy smoking may worsen the problem.

 

DIAGNOSIS
Irritable bowel syndrome is diagnosed after a review of the symptoms and a process of elimination of other disorders. The major symptoms are characteristic of a number of other intestinal disorders, such as colitis, diverticulitis (the inflammation of pockets that form in weakened sections of the intestinal wall) and cancer of the colon.

 

The excessive intestinal spasms that produce the symptoms may be detected in the course of a barium enema, a test in which a chalky liquid mixture is infused into the colon and X-ray photographs are taken. (Since barium has greater density to X-ray than the tissues of the intestines, it can make them show up on X-ray films.) Alternately, or additionally, the doctor may perform a sigmoidoscopic examination in which a hollow tube with viewing instruments is inserted into the anus and passed upward into the colon. These examinations are usually performed to rule out other colon disorders that may produce similar symptoms.

 

TREATMENT
Irritable bowel syndrome, although troublesome and at times anxiety-producing, is not medically serious. Symptoms can interfere with daily living significantly despite lack of structural abnormality of the GI tract. In general, a normal diet is best. If bloating and belching are a problem, foods such as beans and cabbage and other sources of fermentable carbohydrates should be avoided. If the major symptom is diarrhea, it is wise to stay away from laxative foods, such as fruits and fruit juices. Unprocessed bran, taken with plenty of liquid, may help relieve constipation. Often, a high fiber diet or a fiber dietary supplement may be recommended.Illustration of the human gastrointestinal system.

 

In addition, people with irritable bowel syndrome should engage in regular physical exercise. This helps relieve the symptoms of anxiety and also promotes good bowel function. Efforts should be made to deal with any stresses that may be contributing to the problem.

 

For patients who do not respond to dietary and other life-style changes, including a reduction of stress, medications may be prescribed. These may include an anticholinergic agent to reduce the intestinal overactivity, a mild tranquilizer or a sedative.

 

SUMMING UP
The irritable bowel syndrome is a common intestinal disorder characterized by diarrhea, cramps and other symptoms. These symptoms are distressing, but irritable bowel syndrome is not a disease. While the causes of the irritable bowel syndrome are unknown, emotional factor seems to play a major role. Life-style changes and attention to diet may provide sufficient relief; if not, medications may be prescribed.

 

CONTROLLING IBS
The irritable bowel syndrome is a condition characterized by abdominal cramps, diarrhea and constipation. Psychological factor seem to play a major role. Less definite symptoms of IBS may include fatigue, anxiety and difficulty in concentrating. Fortunately, the disorder can be controlled by avoiding triggering foods, increasing dietary bulk, administering antispasmodic drugs, reducing stress and engaging in regular physical exercise.

Frequently Asked Questions
1.1: What is Irritable Bowel Syndrome? 
Irritable Bowel Syndrome (IBS) is part of a spectrum of diseases known as Functional Gastrointestinal Disorders which include diseases such as noncardiac chest pain, nonulcer dyspepsia, and chronic constipation or diarrhea. These diseases are all characterized by chronic or recurrent gastrointestinal symptoms for which no structural or biochemical cause can be found. IBS affects between 25 and 55 million people in the United States and results in 2.5 to 3.5 million yearly visits to physicians. Approximately 20 to 40 percent of all visits to gastroenterologists are due to IBS symptoms. Because there is no diagnostic marker associated with IBS, the diagnosis is one of exclusion and is based on symptoms. Manning and his colleagues were the first to report six symptoms which differentiated IBS from other gastrointestinal diseases. The six 'Manning Criteria' are as follows: 1) relief of abdominal pain with defecation, 2) looser stools with the onset of pain, 3) more frequent bowel movements at onset of pain, 4) abdominal bloating or distention, 5) feelings of incomplete evacuation, and 6) passage of mucus per rectum. In general the more 'Manning Criteria' present the more likely it is that a patient has IBS. While the 'Manning Criteria' are helpful in diagnosing IBS a consensus meeting in Rome, Italy recently further refined these criteria (see 2.1). In addition, since many other gastrointestinal diseases can present with similar symptoms, a diagnosis of IBS should only be made in the right clinical setting

1.2: What is the prevalence of IBS? 
IBS symptoms affects men and women of all ages and of all races. The prevalence of IBS in the general population of Western countries varies from 6 to 22%. IBS affects 14-24% of women and 5-19% of men. The prevalence is similar in Caucasians and African Americans, but appears to be lower in Hispanics. Although several studies have reported a lower prevalence of IBS among older people, the present studies do not allow to definitely conclude whether or not an age disparity exists in IBS. In non-Western countries such as Japan, China, India, and Africa, IBS also appears to be very common. 

1.3: What triggers IBS? 
Many patients with IBS report that their symptoms began during periods of major life stressors such as a divorce, death of a loved one, or school exams. Many patients also report the onset of symptoms during or shortly after recovering from a gastrointestinal infection or abdominal surgeries. Symptoms of IBS have also been known to appear upon the ingestion of a certain food to which the individual is sensitive. The type of food which causes symptoms varies with the individual. (There is no one definite universal food trigger for IBS.) Similarly, a flare of symptoms in a patient with long-standing IBS may be triggered by all of the symptoms listed above, or for no apparent reason.


2.1: What are the symptoms of IBS? 
A number of expert investigators during a meeting in Rome, Italy, developed a consensus definition and criteria for IBS, known as the "Rome" criteria. At least 
3 months of continuous or recurrent symptoms of: 
1. Abdominal pain or discomfort that is: 
   
a. Relieved with defecation and/or 
    b. Associated with a change in frequency of stool; and/or 
    c. Associated with a change in consistency of stool; and 
2. Two or more of the following, at least on one-fourth of occasions or 
   
days: 
   a. Altered stool frequency 
   b. Altered stool form (e.g. watery/loose stools or hard stools) 
   c. Altered stool passage (e.g. sensations of incomplete evacuation 
       after bowel movements, straining, or urgency) 
   d. Passage of mucus and/or 
   e. Bloating or feeling of abdominal distention. 
In addition, a number of other non-colonic symptoms may be present in patients with IBS. These include: nausea, feeling full after eating only a small meal, sensation of urinary urgency, incomplete emptying after urinating, fatigue, and pain during intercourse. 

2.1.1: Does everybody get the same symptoms? 
No. Although the symptoms listed in 2.1 are the most common, each person's experience and presentation will be slightly different. The severity and frequency of abdominal pain or discomfort will also vary from an intermittent abdominal discomfort during stress life events to severe continuous abdominal pain. Likewise, bowel habits can vary. Diarrhea, constipation, or alternating between the two may be the predominant bowel pattern.

3.1: What causes IBS? 
Recent physiological and psychosocial data have emerged to improve our understanding of IBS. A biopsychosocial model of IBS involving physiological, emotional, cognitive, and behavioral factors is now felt to be involved in symptom generation. Physiological factors implicated in the etiology of IBS symptoms include visceral hypersensitivity to spontaneous contractions and to balloon distention of the bowel, autonomic dysfunction including exaggerated colonic motility response to stress and alterations in fluid and electrolyte handling by the bowel, and an alteration in the gastrocolonic response. However, alterations in these physiological parameters are generally found in only a subset of patients and frequently do not correlate with bowel symptoms. Behavioral factors such as stressful life events are reported by up to 60% of IBS patients to be associated with the first onset of the disease or with its exacerbation. Laboratory stressors have also been shown to affect gastrointestinal motility and visceral perception. Cognitive factors such as inappropriate coping styles and illness behavior are common in IBS patients and influence healthcare utilization and clinical outcomes. Emotional and psychiatric factors, such as anxiety and depression, are present in 40 to 60% of IBS patients seeking healthcare with increased prevalence in those patients presenting to tertiary referral centers. IBS patients who have sought medical care are more likely to have abnormal psychological profiles, abnormal illness behaviors, and psychiatric diagnoses than patients with other medical illnesses.

3.2: What is the role of psychosocial factors in IBS? 
Psychiatric diagnoses are present in 42-62% of IBS patients who have sought medical consultation. In comparison, psychiatric diagnoses are present in around 20% of patients with other gastrointestinal diagnoses. The majority of these psychiatric diagnoses are cases of anxiety and depression. Other common diagnoses include somatization disorder and hypochondriasis. Stress can affect the functioning of the gastrointestinal tract of all people, and particularly those with IBS. Several studies have shown that IBS patients are more likely to report that stress changes their stool pattern and leads to abdominal pain than people without bowel problems. In one study 65% of IBS patients reported a severe stressful life event prior to developing IBS. The kinds of psychological stressors often reported by patients with IBS vary considerably, but include: loss of a parent or spouse through death, divorce, or separation, and sometimes is accompanied by feelings of unresolved grief, and also significant life changes which demand many social and personal adjustments such as moving to a new job or a new city. A history of physical or sexual abuse in childhood has also been found to be associated with chronic abdominal pain and IBS in some patients. 

3.2.1: Is IBS life-threatening? 
No, however, IBS is serious. Patients with IBS have a higher rate of hospitalizations, work absenteeism, feelings of poor quality of life, and abdominal surgeries than healthy controls and patients with other gastrointestinal illnesses. In the general population, people with IBS symptoms missed more than 3 times as many work days than did people without bowel symptoms. 

3.2.2: Will IBS lead to cancer? 
No. 

3.2.3: Does IBS lead to IBD (Crohn's, ulcerative colitis)? 
No. IBS symptoms are often present in patients with IBD however there is no evidence to suggest that IBS leads to IBD. 

3.3: Will my IBS eventually go away, or is it here for the rest of my life? 
IBS symptoms may fluctuate over time. In one study, more than 50% of IBS patient remained symptomatic 5 years after their initial diagnosis.

4.1: How do I know for sure if I have IBS? 
Since there is no diagnostic marker associated with IBS, the diagnosis is based on symptoms and by excluding other diseases which may have a similar presentation. The extent of the medical evaluation which is necessary prior to making a diagnosis of IBS will vary depending on the duration of symptoms, the patient's age and clinical presentation. For example, recent onset of symptoms in an older patient will require more extensive testing than a younger person with unchanged symptoms for many years. Most patients, however, will be given a thorough physical exam which is performed mainly to rule out other medical illnesses. If further testing is necessary it will usually be directed toward the predominant symptom. For example, patients with significant diarrhea will often undergo stool tests for ova and parasite, and malabsorption if clinically indicated. On the other hand, patients with constipation will often undergo tests such as radiopaque marker studies (Sitzmarker) for colonic functioning and anorectal manometry for pelvic floor functioning. Most patients over the age of 50 years should have a flexible sigmoidoscopy. In addition, if occult blood is found by either rectal exam or on hem-occult testing a colonoscopy may be necessary. Some commonly performed tests are listed below: - Lower G.I. x-ray (a.k.a. the barium enema) - Small bowel series x-ray - Stool parasite culture - Flexible sigmoidoscopy and/or colonoscopy It is important to note that the ONLY way to be absolutely certain you have IBS is through a doctor's diagnosis. 

4.1.2: Is IBS really a "cop-out" diagnosis? 
Should I just accept it? Many times a person may think that he or she is being "slighted" by being given a diagnosis of IBS. Unfortunately, to some doctors, IBS is not considered a "true" disease, but rather an unimportant minor condition (when in reality it is hardly all that "minor" to those who have to deal with it), and therefore may not be given the medical attention it deserves. Don't despair; there ARE competent doctors out there who are very good at dealing with IBS cases. A good doctor won't just tell you that you have IBS and give up on you. He or she should be willing to go over your questions and concerns, and outline and monitor a program of treatment for your individual case of IBS. If you suspect that you have not had a thorough enough examination for other diseases before the doctor tells you that you have IBS, you should seek a second opinion.

5.1: What are the treatments for IBS? 
The treatment of IBS is based on the severity and the nature of each person's symptoms and the effect psychosocial factors are having on their illness behavior. Therefore, each person's therapy is tailored to their symptoms and may include one or more of the following: lifestyle changes, pharmacological treatment, and psychological treatment. Therefore, there really is no "one" good general treatment for IBS. Different things work for different people, and unfortunately the only way to know exactly what works for you is by trial-and-error. 

5.1.1: What is the role of fiber therapy in IBS? 
Fiber is the non-digested part of plant food and adds bulk to the stools by absorbing water. There are two types of fiber: soluble and insoluble. Soluble fiber dissolves in water and is found in oat bran, barley, peas, beans, and citrus fruits. Insoluble fiber are found in wheat bran and some vegetables. Fiber increases the transit time of the colon and decrease the pressures within the colon. However, the role of fiber in the treatment of IBS has not been well established. One study showed that the response to bran in terms of daily stool weight, bowel frequency and symptoms was determined more by pre-existing psychometric variables such as anxiety and depression that the amount or nature of the bulking agent administered. From our experience, however, patients with mild constipation predominant IBS may derive some benefit. Fiber can be added to the diet through the eating of more fiber-rich foods, or by taking fiber supplements (common brands are Metamucil, Citrucel, and FiberCon). 

5.1.2: What sort of dietary modifications are required? 
In some cases, certain foods can aggravate IBS symptoms and should be avoided. In particular, lactose in lactose deficient individuals, gas producing vegetables such as beans and broccoli, fatty foods, and alcohol. It is should be noted however that while these foods can exacerbate IBS symptoms, they are not the sole cause of typical IBS symptoms. To determine which foods trigger which symptoms, one often needs to start with very basic bland diet and gradually add one new food each day and record any symptoms associated with that particular food. 

5.1.3: What conventional prescription medications are used to treat IBS?
Conventional medications used in the treatment of IBS include (but are not limited to): 
- Anti-spasmodic drugs like Bentyl and Levsin are considered to part of the class of anti-cholinergic drugs. Anti-cholinergic drugs act by decreasing the abnormal sensitivity of choninergic (muscarinic M2) receptors in gut smooth muscle. Significant improvement in abdominal pain and rectal urgency have been reported in some studies compared to placebo in short-term trials. However, there is no evidence that anticholinergic are more efficacious than placebo in the longer term. 
- Antacids/anti-gas medications (e.g. Simethicone or BEANO). There is no current data which supports their use in the treatment of IBS symptoms, though many people report that they aid in the reduction of embarrassing flatulence and the accompanying lower abdominal pain.
- Anti-diarrhea medications/Opioid-receptor agonist (e.g. loperamide or "immodium") Loperamide is an mu opioid receptor agonist which does not cross the blood-brain barrier. It delays small and large bowel transit, increases the frequency of small bowel phase 3 of the migrating motor complexes, decreases intestinal secretory activity, and increases rectal sphincteric muscle tone. Some studies have shown improvement in diarrhea, rectal urgency, and abdominal pain in IBS. 
- Prokinetic Agents (e.g. Cisapride or "Propulsid"). A prokinetic drug which is a 5HT4 agonist and a 5HT3 antagonist. Cisapride has been reported to help in gastroesophageal reflux disease and dyspepsia related to delayed gastric emptying. Its efficacy in constipation predominant IBS, however, has not been well established. 
- Antidepressants. Tricyclic antidepressants (e.g. amitriptyline, imipramine, and despramine) or serotonin reuptake inhibitors (e.g. fluoxetine, sertraline, and paroxetine) are commonly used to treat IBS. Although commonly used in IBS patients their efficacy is still being debated. Even though antidepressants are often used in patients with associated depression, antidepressants appear to improve symptoms independent of their antidepressive effects. One study using despramine found this drug to be superior to both atropine (an anticholinergic- which is a common side-effect of the tricyclic antidepressants) and placebo in relieving both gastrointestinal symptoms and depression. Therapeutic effect can take as long as 4-6 weeks and therefore therapeutic trial should continue at least this long. 
- Smooth muscle relaxants (e.g. mebeverine (not yet available in the U.S.) and peppermint oil) have direct relaxant properties on gut smooth muscle. Placebo controlled trials, however, have not produced any consensus on their efficacy in IBS.