Patients with IBS usually experience abdominal pain or discomfort associated with diarrhoea or constipation; some may alternate between diarrhoea and constipation.

In Singapore, about 13% of patients have diarrhoea-predominant IBS and 51% have constipation-predominant IBS. Abdominal pain can occur anywhere in the abdomen, even in the so-called "stomach" or gastric area and pelvic area. Patients may also experience feelings of abdominal discomfort, such as bloating, stretching, tightness. Some may have confusing symptoms, such as backache and chest discomfort, as irritation of the bowel can give rise to pain in these areas.

Diarrhoea associated with IBS is not necessarily severe, as some patients have only two or three bowel movements a day, and the stools are usually loose but not watery. More disturbing for the patient is the associated urgency. This is when the patient feels the urge to defecate and has to rush to find a bathroom to avoid an accident. Quite often, this occurs when the patient is eating out and it can be embarrassing. Some patients have a particularly unfortunate combination of a weak anus muscle and a sensitive bowel so that they are unable to control themselves and may have accidental leakage.

Other patients experience constipation, with some having a bowel movement once in 3 days or even once a week. These patients can experience a great deal of discomfort when they have not had a bowel movement. This can range from pain to bloating to poor appetite. Some spend a long time in the bathroom and strain, using a lot of effort to produce very small, pellet-like stools.

Incomplete Emptying

Many patients have disturbed defecation. Some may have a feeling of incomplete defecation–the sensation that the bowels have not been completely emptied after a bowel movement. This is often frustrating, as the patient must keep going back to the bathroom to make unproductive attempts. At other times, it is disruptive to work or travel as the patient must interrupt an activity to find a bathroom.

Gas and Bloating

Some patients may have only mild bowel disturbances and are more bothered by symptoms which they attribute to gas. They may complain of bloating, stomach fullness, a feeling of stretching in the abdomen, flatulence or a noisy, rumbling stomach. Some may not pass much gas, but wish that they could.

Others Symptoms

IBS patients may even experience symptoms seemingly unrelated to the bowels. These can include "gastric" symptoms, such as heartburn and frequent belching. Some also experience problems with urination; they have an irritable bladder in addition to their irritable bowel. Just like their bowels, they may have a frequent urge to pass urine, or feel that they have not completely emptied their bladder even after passing urine and keep returning to the bathroom. Some women with IBS may experience pain during sexual intercourse.

IBS symptoms may be confused with other conditions. Patients who experience pain in their upper right side, associated with bloating and frequent belching, may be told that their symptoms are due to gallstones. The confusion arises because many patients who have gallstones actually do not have any symptoms from the gallstones.

In fact, about 75% of people with gallstones do not feel any pain or discomfort. The gallstone is actually an incidental finding. The pain from IBS can also be mistaken for appendicitis, if it occurs in the lower right corner of the abdomen. Women with IBS often think their lower abdominal pain comes from a problem in the uterus or ovaries. This is because the symptoms of IBS can be affected by the menstrual cycle. Bloating and abdominal pain from IBS worsens during menses. Many women find that their constipation is particularly bad during the week before their menses, others may get loose stools during their menses.

病症

腹泻 IBS 病人的腹泻问题多不严重，有些病人一天里只如厕2至3次，粪便多松软但不水泄。扰乱病人的是上厕所的急迫性。病人必须尽快找到厕所，否则意外会发 生。经常，病人在外用餐发生这种情形，可真难为情。有些病人特别不幸，兼有肛肌无力和敏感性的肠胃，以致失控而导致外漏。

便秘

有些病人却经历便秘的不适。有的3天甚至一个星期才排粪一次。这些病人由于肠胃不通而得忍受各种痛楚，从疼痛，腹胀到失去胃口等。有的病人上厕所时，费时又费力，只排出一些硬粪粒。

排便不清

许多病人的排便情况被扰乱了。有些则有排便未清的感觉，必须连续上厕所却无所作为，受尽挫折之苦。有时病人不论在工作中或旅行中，必须中止活动而找洗手间，甚为不便。 胃气胀 有的病人因肠道问题而受的困扰不大，但为了多种和气有关的病症而烦恼。他们控诉胃气涨，胃感觉饱涨，腹部彭胀感，肠胃气胀而引起咕咕声，但愿能把气体排去。

其他病症

IBS 患者甚至会有其他与肠胃无关的病症，这可能包括胃病的症状，例如胃灼热，经常呃气，有些还有排尿的问题。除了肠道易激惹，还有过敏性的膀胱，和他们的过敏 性肠道相似他们经常有要排尿的欲望，或者觉得排尿后膀胱还不清，而要重返洗手间。有些女性患者还会于性交时感觉疼痛。

IBS病症可能会与 其他病情混淆。病人因肠胃气胀，经常呃气而引起肚子右上部疼痛，会被误诊为胆石。搞错的原因是由于许多胆结石病人并没有症状。约有70%的胆石病人不觉得 任何病痛或不适。其胆石多是在无意中被发现的。IBS的病痛如果是在肚子右下部，也可能被诊断为盲肠炎。女性患者经常以为她们下腹部的疼痛是子宫或卵巢的 问题，这是由于IBS的症状会受经期的影响。在月经期间，IBS病情的气胀和腹痛会恶化，许多女性的便秘问题，在月经前一星期特别严重，有些却在月经期间 粪便松软。