Dr. Qin Rao answers common questions about treating irritable bowel syndrome with constipation.

Irritable bowel syndrome with constipation (IBS-C) is a functional disorder in which people develop symptoms of abdominal pain, bloating, and gas, with bowel movements dominated particularly by constipation.

IBS-C is one of the most common GI disorders diagnosed by a doctor and has a heavy socioeconomic burden.

It’s more prominent in women, people younger than age 50, and in people with a history of anxiety, depression, and other mental health conditions. The exact cause of IBS-C is unknown, but there are several working theories.

People with symptoms of IBS-C that don’t respond to lifestyle changes or over-the-counter (OTC) medications should see a doctor.

There are a few alarm symptoms for which a person should see a doctor sooner. These include:

  • rectal bleeding
  • unintentional weight loss
  • unexplained iron deficiency anemia
  • nocturnal symptoms
  • family history of colon cancer, inflammatory bowel disease, or celiac disease.

During a doctor’s visit, a detailed history will be taken. Doctors ask questions about the severity and duration of your symptoms and what lifestyle and OTC treatments you’ve already tried.

They might also ask questions to rule out alternative diagnoses and look for alarm symptoms before diagnosing you with IBS-C. People over the age of 45 might be asked to have a colonoscopy.

The doctor will perform a physical exam. Most people with IBS-C will have a normal abdominal exam, although some might have belly pain or palpable stool on the exam.

There are no specific lab tests for IBS-C, but a doctor might request:

  • a blood count to rule out anemia
  • a thyroid level test to rule out hypothyroidism
  • a calcium level test to rule out elevated calcium (a potential cause of constipation)

They might also perform an abdominal X-ray to assess the extent of the constipation.

If the workup is negative and you’re diagnosed with IBS-C, a doctor will then discuss prescription medications if you did not respond to lifestyle or OTC treatments.

People with IBS-C should try to:

  • Minimize stress through methods such as meditation.
  • Incorporate moderate to vigorous physical activity 3–5 days a week.
  • Get enough sleep.
  • Drink enough water.
  • Eat a high fiber diet of 25–35 grams of fiber daily, depending on sex and weight.
  • Avoid high gas-producing foods by attempting a trial of the low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet.

People with IBS-C should start with OTC fiber supplements to help move their bowels.

I recommend starting with psyllium husk or methylcellulose and taking enough to meet your daily dietary recommendations. So, for example, if a person needs 30 grams of fiber a day and only intakes 20 grams, they should increase their intake from food or take a fiber supplement to make up the difference.

Be aware that taking excessive amounts of fiber without drinking enough water can make you gassy and bloated.

If you have reached your fiber goal, you can take polyethylene glycol (Miralax) as the next step. Polyethylene glycol is safe to take once or twice daily and can be titrated according to your needs.

Be aware that polyethylene glycol only treats constipation and not abdominal pain, although relief of constipation might improve bloating, gas, and abdominal pain. It can paradoxically also cause increased gassiness and bloating. Drink plenty of water to avoid dehydration.

If these steps don’t work, see a doctor for evaluation for prescription medications.

Over-the-counter laxatives such as fiber and polyethylene glycol are safe to take long term as long as you follow instructions. They can cause bloating and dehydration, so make sure to drink enough water.

Medications such as senna glycoside can cause a condition called melanosis coli and should be avoided long term.

Magnesium supplements should be avoided in people with kidney damage and can rarely cause paralysis and shortness of breath. They also can cause nausea, vomiting, and abdominal cramping.

If you’ve tried lifestyle changes and OTC treatment options without success or if you have alarming symptoms, you should see your doctor.

Current prescription treatments available for IBS-C include:

  • linaclotide (Linzess)
  • plecanatide (Trulance)
  • lubiprostone (Amitiza)
  • tenapanor (Ibsrela)
  • Prucalopride (Motegrity — used off-label for IBS-C)

Prescription medications used to treat IBS-C generally help with bloating, abdominal pain, and constipation. In regard to bloating and abdominal pain alone, a number of treatment options are available, including:

  • antibiotics such as rifaximin (Xifaxan), which sometimes can help treat a condition called SIBO (small bowel bacterial overgrowth)
  • dicyclomine (Bentyl) or hyoscyamine (Levsin), which can treat gut spasms
  • menthol (Ibgard), which helps relax the gut

There’s mixed data on the efficacy of some of these treatments.

Antidepressants have also been shown to be beneficial in treating symptoms of IBS-C, although some can worsen constipation and should be avoided.

The most common side effect of promotility agents is they can cause worsening bloating, gas, abdominal pain, dizziness, and diarrhea. Any medication can cause an allergic reaction.

Plecanatide can cause an increased risk of upper respiratory infections (URIs).

Prucalopride is a serotonin agonist and is approved for chronic idiopathic constipation. It’s sometimes used off-label for IBS-C, especially if the condition is refractory (resistant) to other medications.

Because of the serotonin component, it has a rare but increased risk of suicidal ideation and worsening depression. It can also interact with other antidepressants that an individual is taking.

People should try other alternatives before starting this medication and talk with their doctors before starting this medication. They should be monitored closely when they start the medication.

People who do not respond to OTC or prescription medication may be referred to a motility specialist. A colonoscopy might also be considered.

A motility specialist might consider doing additional testing on a patient, such as a sitz marker test to assess gut motility or anorectal testing to rule out pelvic floor dysfunction.

People might also benefit from behavioral modification or hypnosis.

Dr. Qin Rao is an ABMS board certified internal medicine physician specializing in gastroenterology and hepatology. He is currently a practicing physician at Manhattan Gastroenterology in New York City, specializing in irritable bowel syndrome, inflammatory bowel disease, dyspepsia, and hemorrhoid treatment.