Irritable bowel syndrome (IBS) is a chronic disorder that affects the large intestine. Symptoms can include abdominal pain, cramping, bloating, gas, and constipation or diarrhea. IBS is considered a functional disorder, which is a condition where the normal function of the body is impaired, but the cause has remained largely undetected and not well understood. IBS is characterized by chronic abdominal pain, but there are no structural or biochemical causes that can explain the symptoms. This condition is believed to be a result of dysregulation of stretch receptors in the GI tract. Women are more often affected by IBS than men.

IBS can be grouped into the following categories:

• IBS-D where diarrhea is predominant
• IBS-C where constipation is predominant
• IBS-A or IBS-M where stool patterns alternate between constipation and diarrhea. The A means alternating and the M means mixed, but they both refer to the same pattern.
• IBS-P where pain is predominant.

There is no definitive test to diagnose IBS. After ruling out other possibilities for the discomfort, a positive diagnosis for IBS is often made by excluding other possible causes of discomfort and using the ROME IV criteria. This diagnostic tool involves observance of recurrent abdominal pain on average at least 1 day/week in the last 3 months associated with two or more of the following criteria: relief of pain or discomfort with defecation, onset of pain or discomfort associated with a change in bowel movement frequency, and onset of pain or discomfort associated with a change in stool appearance.

Management of IBS is different for everyone, but it generally helps to limit stress, get enough sleep, exercise regularly, drink plenty of fluids, eat high-fiber foods, and avoid foods that trigger symptoms. Some common foods that induce symptoms include refined grains, processed foods like chips and cookies, coffee, carbonated drinks, high protein diets, dairy products (especially cheese), and alcohol. Medications tailored to the specific type of IBS that an individual has can also be used. Several anticholinergic drugs or drugs with anticholinergic effects are used to help IBS-D because they have a constipating effect. These include hyoscyamine sulfate (Levsin), diphenoxylate/atropine (Lomotil), and the tricyclic antidepressant amitriptyline (Elavil). Activation of 5HT-3 receptors (a type of serotonin receptor) in the gut increase peristalsis, so blocking them with the 5HT-3 antagonist alosetron (Lotronex) can be useful for IBS-D. Some drugs for the treatment of IBS-C are lubiprostone (Amitiza) and linaclotide (Linzess), which are chloride channel activators that increase chloride in the lumen of the gut that then draws sodium ions and water into the lumen.