Symptoms of IBS vary but are usually present for a long time. The most common include:

• Belly pain, cramping or bloating that is related to passing stool.
• Changes in appearance of stool.
• Changes in how often you are passing stool.

Other symptoms that are often related include sensation of incomplete evacuation and increased gas or mucus in the stool.

When to see a doctor

See a healthcare professional if you have a persistent change in bowel habits or other symptoms of IBS. They may mean a more serious condition, such as colon cancer. More-serious symptoms include:

• Weight loss.
• Diarrhea at night.
• Rectal bleeding.
• Iron deficiency anemia.
• Unexplained vomiting.
• Pain that isn't relieved by passing gas or stool.

The exact cause of IBS isn't known. Factors that appear to play a role include:

• Muscle contractions in the intestine. The walls of the intestines are lined with layers of muscle that contract as they move food through the digestive tract. Contractions that are stronger and last longer than usual can cause gas, bloating and diarrhea. Weak contractions can slow food passage and lead to hard, dry stools.
• Nervous system. Issues with the nerves in the digestive system may cause discomfort when the belly area, called the abdomen, stretches from gas or stool. Poorly coordinated signals between the brain and the intestines can cause the body to overreact to changes that typically occur in the digestive process. This can result in pain, diarrhea or constipation.
• Severe infection. IBS can develop after a severe bout of diarrhea caused by bacteria or a virus. This is called gastroenteritis. IBS also might be associated with a surplus of bacteria in the intestines, known as bacterial overgrowth.
• Early-life stress. People exposed to stressful events, especially in childhood, tend to have more symptoms of IBS.
• Changes in gut microbes. Examples include changes in bacteria, fungi and viruses, which typically live in the intestines and play a key role in health. Research indicates that the microbes in people with IBS might differ from those in people who don't have IBS.

Triggers

Symptoms of IBS can be triggered by:

• Food. The role of food allergy or intolerance in IBS isn't fully understood. A true food allergy rarely causes IBS. But many people have worse IBS symptoms when they eat or drink certain foods or beverages. These include wheat, dairy products, citrus fruits, beans, cabbage, milk and carbonated drinks.
• Stress. Most people with IBS experience worse or more-frequent symptoms during periods of increased stress. But while stress may make symptoms worse, it doesn't cause them.

Many people have occasional symptoms of IBS. But you're more likely to have the syndrome if you:

• Are young. IBS occurs more often in people under age 50.
• Are female. In the United States, IBS is more common among women. Estrogen therapy before or after menopause also is a risk factor for IBS.
• Have a family history of IBS. Genes may play a role, as may shared factors in a family's environment or a combination of genes and environment.
• Have anxiety, depression or other mental health issues. A history of sexual, physical or emotional abuse also might be a risk factor.

Long-lasting constipation or diarrhea can cause hemorrhoids.

In addition, IBS is associated with:

• Poor quality of life. Many people with moderate to severe IBS report poor quality of life. Research indicates that people with IBS miss three times as many days from work as do those without bowel symptoms.
• Mood disorders. Experiencing the symptoms of IBS can lead to depression or anxiety. Depression and anxiety also can make IBS worse.

There's no test to definitively diagnose IBS. A healthcare professional is likely to start with a complete medical history, physical exam and tests to rule out other conditions, such as celiac disease and inflammatory bowel disease (IBD).

After other conditions have been ruled out, a care professional is likely to use one of these sets of diagnostic criteria for IBS:

• Rome criteria. These criteria include belly pain and discomfort averaging at least one day a week in the last three months. This also usually occurs with at least two of the following: pain and discomfort related to defecation, a change in the frequency of defecation, or a change in stool consistency.
• Type of IBS. For the purpose of treatment, IBS can be divided into four types, based on symptoms: constipation-predominant, diarrhea-predominant, mixed or unclassified.

A healthcare professional also will likely explore whether you have other symptoms that might suggest another, more serious condition. These include:

• Onset of symptoms after age 50.
• Weight loss.
• Rectal bleeding.
• Fever.
• Nausea or repeated vomiting.
• Belly pain, especially if it's not related to passing stool, or occurs at night.
• Diarrhea that is ongoing or awakens you from sleep.
• Anemia related to low iron.

If you have these symptoms, or if an initial treatment for IBS doesn't work, you'll likely need more tests.

Additional tests

A healthcare professional may recommend several tests to help with diagnosis.

Diagnostic procedures can include:

• Colonoscopy. In colonoscopy, a camera attached to a small, flexible tube is used to examine the entire length of the colon.
• CT scan. This test produces images of the abdomen and pelvis that might rule out other causes of symptoms, especially if belly pain is present.
• Upper endoscopy. A long, flexible tube is inserted down the throat and into the esophagus, which is the tube connecting the mouth and stomach. A camera on the end of the tube provides a view of the upper digestive tract. During an endoscopy, a tissue sample called a biopsy may be collected. A sample of fluid may be collected to look for overgrowth of bacteria. This test may be recommended if celiac disease is suspected.

Laboratory tests can include:

• Lactose intolerance tests. Lactase is an enzyme needed to digest the sugar found in dairy products. If a person doesn't produce lactase, they may have problems like those caused by IBS, including belly pain, gas and diarrhea. A healthcare professional may order a breath test or ask you to remove milk and milk products from your diet for several weeks.
• Breath test for bacterial overgrowth. A breath test also can determine if there is bacterial overgrowth in the small intestine. Bacterial overgrowth is more common among people who have had bowel surgery or who have diabetes or some other disease that slows down digestion.
• Stool tests. Stool might be examined for bacteria, parasites or the presence of bile acid. Bile acid is a digestive liquid produced in the liver. Stool studies also can check to see if the intestine has trouble taking in nutrients. This is a condition known as malabsorption.

Treatment of IBS focuses on relieving symptoms so that you can live as symptom-free as possible.

Mild symptoms often can be controlled by managing stress and by making changes in diet and lifestyle. Try to:

• Stay away from foods that trigger symptoms.
• Eat high-fiber foods.
• Drink plenty of fluids.
• Exercise regularly.
• Get enough sleep.

A healthcare professional might suggest eliminating these foods:

• High-gas foods. If bloating or gas are an issue, don't consume carbonated and alcoholic beverages or certain foods that may lead to increased gas.
• Gluten. Research shows that some people with IBS report improvement in diarrhea symptoms if they stop eating gluten even if they don't have celiac disease. Gluten is found in foods containing wheat, barley and rye.
• FODMAPs. Some people are sensitive to certain carbohydrates such as fructose, fructans, lactose and others, known as FODMAPs — fermentable oligosaccharides, disaccharides, monosaccharides and polyols. FODMAPs are found in certain grains, vegetables, fruits and dairy products.

A dietitian can help with these diet changes.

If problems are moderate or severe, a healthcare professional might suggest counseling — especially if depression or stress tends to make symptoms worse.

Based on symptoms, medicines may be recommended, including:

• Fiber supplements. Taking a supplement such as psyllium husk (Metamucil) with fluids may help control constipation.
• Laxatives. If fiber doesn't help constipation, nonprescription laxatives, such as magnesium hydroxide oral (Milk of Magnesia) or polyethylene glycol (Miralax), may be recommended.
• Antidiarrheal medicines. Nonprescription medicines, such as loperamide (Imodium A-D), can help control diarrhea. A care professional also might prescribe a bile acid binder, such as cholestyramine (Prevalite), colestipol (Colestid) or colesevelam (Welchol). Bile acid binders can cause bloating.
• Anticholinergic medicines. Medicines such as dicyclomine (Bentyl) can help relieve painful bowel spasms. They are sometimes prescribed for people who have bouts of diarrhea. These medicines are generally safe but can cause constipation, dry mouth and blurred vision.
• Tricyclic antidepressants. This type of medicine can help relieve depression, but it also blocks the activity of neurons that control the intestines. This may help reduce pain. If you have diarrhea and belly pain without depression, a healthcare professional may suggest a lower than typical dose of imipramine (Tofranil), desipramine (Norpramin) or nortriptyline (Pamelor). Side effects — which might be reduced if you take the medicine at bedtime — can include drowsiness, blurred vision, dizziness and dry mouth.
• SSRI antidepressants. Selective serotonin reuptake inhibitor (SSRI) antidepressants, such as fluoxetine (Prozac) or paroxetine (Paxil), may help if you are depressed and have pain and constipation.
• Pain medicines. Pregabalin (Lyrica) or gabapentin (Neurontin) might ease severe pain or bloating.

Medicines specifically for IBS

Medicines approved for certain people with IBS include:

• Alosetron (Lotronex). Alosetron is designed to relax the colon and slow the movement of waste through the lower bowel. It can be prescribed only by providers enrolled in a special program. Alosetron is intended only for severe cases of diarrhea-predominant IBS in women who haven't responded to other treatments. It is not approved for use by men. Alosetron has been linked to rare but important side effects, so it only should be considered when other treatments aren't successful.
• Eluxadoline (Viberzi). Eluxadoline can ease diarrhea by reducing muscle contractions and fluid secretion in the intestine. It also helps increase muscle tone in the rectum. Side effects can include nausea, belly pain and mild constipation. Eluxadoline also has been associated with pancreatitis, which can be serious and more common in certain people.
• Rifaximin (Xifaxan). This antibiotic can decrease bacterial overgrowth and diarrhea.
• Lubiprostone (Amitiza). Lubiprostone can increase fluid secretion in the small intestine to help with the passage of stool. It's approved for women who have IBS with constipation, and is generally prescribed only for women with severe symptoms that haven't responded to other treatments.
• Linaclotide (Linzess). Linaclotide also can increase fluid secretion in your small intestine to help you pass stool. Linaclotide can cause diarrhea, but taking the medicine 30 to 60 minutes before eating might help.

Potential future treatments

Researchers are investigating new treatments for IBS, such as fecal microbiota transplantation (FMT). Considered investigational at this time, FMT restores healthy intestinal bacteria by placing another person's processed stool into the colon of a person affected by IBS. Clinical trials to study fecal transplants are currently underway.

Simple changes in your diet and lifestyle often provide relief from IBS. Your body typically needs time to respond to these changes. Try to:

• Experiment with fiber. Fiber helps reduce constipation but also can worsen gas and cramping. Try slowly increasing the amount of fiber in your diet over a period of weeks with foods such as whole grains, fruits, vegetables and beans. A fiber supplement might cause less gas and bloating than fiber-rich foods.
• Stay away from problem foods. Get rid of foods that trigger your symptoms.
• Eat at regular times. Don't skip meals, and try to eat at about the same time each day to help regulate bowel function. If you have diarrhea, you may find that eating small, frequent meals makes you feel better. But if you're constipated, eating larger amounts of high-fiber foods may help move food through your intestines.
• Exercise regularly. Exercise helps relieve depression and stress, stimulates contractions of your intestines, and can help you feel better about yourself. Ask a healthcare professional about an exercise program.

The role of alternative therapies in relieving IBS symptoms is unclear. Ask a healthcare professional before starting any of these treatments. Alternative therapies include:

• Hypnosis. A trained professional teaches you how to enter a relaxed state and then guides you in relaxing your abdominal muscles. Hypnosis may reduce belly pain and bloating. Several studies support the long-term effectiveness of hypnosis for IBS.
• Peppermint. Studies show that, in people who have IBS with diarrhea, a specially coated pill that slowly releases peppermint oil in the small intestine (enteric-coated peppermint oil) eases bloating, urgency, abdominal pain and pain while passing stool.
• Probiotics. Probiotics are "good" bacteria that typically live in your intestines and are found in certain foods, such as yogurt, and in dietary supplements. Recent studies suggest that certain probiotics may relieve IBS symptoms, such as belly pain, bloating and diarrhea.
• Stress reduction. Yoga or meditation can help relieve stress. You can take classes or practice at home using books, videos or apps that can be downloaded to a smartphone.

You may be referred to a provider who specializes in the digestive system, called a gastroenterologist.

What you can do

• Be aware of any pre-appointment restrictions, such as restricting your diet before your appointment.
• Write down your symptoms, including any that may seem unrelated to the reason why you scheduled the appointment.
• Write down any triggers to your symptoms, such as specific foods.
• Make a list of all your medicines, vitamins and supplements.
• Write down your key medical information, including other conditions.
• Write down key personal information, including any recent changes or stressors in your life.
• Write down questions to ask your provider.
• Ask a relative or friend to go with you, to help you remember what the healthcare professional says.

Questions to ask your doctor

• What's the most likely cause of my symptoms?
• What tests do I need? Is there any special preparation for them?
• What treatment approach do you recommend? Are there any side effects associated with these treatments?
• Should I change my diet?
• Are there other lifestyle changes that you recommend?
• Do you recommend that I talk with a counselor?
• I have other health problems. How can I best manage these conditions together?
• If I have IBS, how long will it take for me to see improvement from the therapy you have prescribed?

In addition to the questions that you've prepared, don't hesitate to ask questions during your appointment anytime you don't understand something.

What to expect from your doctor

You'll likely be asked a few questions. Being ready to answer them may leave time to go over points you want to spend more time on. You may be asked:

• What are your symptoms, and when did they begin?
• How severe are your symptoms? Are they continuous or occasional?
• Does anything seem to trigger your symptoms, such as foods, stress or — in women — your menstrual period?
• Have you lost weight without trying?
• Have you had fever, vomiting or blood in your stools?
• Have you recently experienced significant stress, emotional difficulty or loss?
• What is your typical daily diet?
• Have you ever been diagnosed with a food allergy or with lactose intolerance?
• Do you have any family history of bowel disorders or colon cancer?
• How much would you say your symptoms are affecting your quality of life, including your personal relationships and your ability to function at school or work?

What you can do in the meantime

While you wait for your appointment:

• Ask family members if any relatives have been diagnosed with inflammatory bowel disease or colon cancer.
• Start noting how often your symptoms occur and any factors that seem to trigger them.