As a primary care physician, there’s a good chance you’ll see a patient with constipation this week. Each year, there are 2.5 million doctor visits for constipation in the US. Constipation can be caused by not enough water and fiber intake, but it can also be caused by common medications or disease processes such as colon cancer, Parkinson’s disease, diabetes, and thyroid disorders.

If the problem is new, rule out colon cancer first, said Waqar Qureshi, MD, professor of gastroenterology at Baylor College of Medicine, Houston. “Anybody in their thirties or forties who suddenly develops constipation needs a colonoscopy.”

A change in pattern merits investigation, he said, and suggested that concerned doctors forgo colon cancer stool tests. Inconclusive results or false positives lead to colonoscopy anyway.

Define Constipation

“Constipation means wildly different things to different people,” said Trisha Pasricha, MD, MPH, assistant professor of medicine at Harvard Medical School, Boston, and author of You’ve Been Pooping All Wrong, out this month. “Some are convinced they’re constipated if they don’t go every day. Others have been straining through painful, infrequent stools for years and consider it normal,” she said.

“Clinically, we use the Rome IV criteria— fewer than three spontaneous bowel movements per week, often accompanied by straining, hard stools, or a sense of incomplete evacuation — but most patients have never heard of that,” Pasricha said.

Qureshi shows patients the Bristol stool chart and asks where they fall. Of the seven classifications; one to two are small, lumpy, and hard; three to four show healthy, soft stools; and five to seven are watery. “If you’re passing pebbles every day, you are regular, but you’re constipated,” he said.

Look for Constipation-Inducing Medications

About 11% of constipation cases are caused by common medications, according to a 2024 report.

Ask about vitamins and supplements too, said Julie Stefanski, RDN, spokesperson, Academy of Nutrition & Dietetics. Iron and calcium (found in some antacids) contribute to being blocked.

Adjusting medications is one of the most underutilized levers in managing constipation, said Pasricha, who named offenders such as calcium-channel and beta blockers, and anticholinergic agents. “And now,” she said, “everyone’s on a GLP-1.”

Qureshi agreed. The whole gastrointestinal tract slows down on weight-loss drugs and, he said, constipation from popular GLP-1 agonists is increasingly common.

Find the Root Cause

Besides cancer, constipation may be related to irritable bowel syndrome, diabetes, hypothyroidism, or Parkinson’s disease. Do tests to rule these out depending on results with fiber, laxatives, and medication changes.

“Parkinson’s begins outside the brain for many people, and they experience constipation decades before the classic symptoms,” Pasricha said, referring to the “gut-first” hypothesis, which suggests that the disease is triggered by early microbiome changes in the gastrointestinal tract.

Another overlooked cause of constipation in men and women? An outlet disorder. If a patient hasn’t had success with laxatives, the cause could be rectal or pelvic floor dyssynergia, said Qureshi, which occurs if the anal sphincters contract when they’re supposed to relax.

Considered a learned behavior, dyssynergia can be treated with pelvic floor therapy.

Likely Culprits: A Lack of Fiber, Water

According to the Academy of Nutrition and Dietetics, most people need about 14 g of fiber for every 1000 calories. This means the daily goal for most is around 28-32 g/d; most people get less than half of that. 

“As a nation, we’re constipated because none of us get enough fiber,” said Qureshi.

Getting an extra 15-18 g of fiber from food is a big challenge. “Increasing fiber is among the best studied lifestyle interventions, but at the same time, changing our diets is notoriously difficult and often our changes aren’t sustainable.” Pasricha acknowledged.

Many overestimate their intake. “Patients eat whole wheat bread that has 2 g of fiber per slice, and don’t realize, when you do the math, it doesn’t get them even close to the actual recommended goals,” she explained.

A fiber supplement made with psyllium can be a more realistic way to show how effective fiber can be and can make a big difference within 1 or 2 weeks of starting, according to Pasricha.

Plus, flatulence comes with abrupt fiber increases. “Patients who go from 5 g to 20 g overnight are going to feel terrible.” Start low and go slow, she said. Add a few grams per week, spread it throughout the day, and increase water intake proportionally.

Fiber needs time and water to work. “It is helpful to give patients a personalized fluid goal and have them track fluid intake,” Stefanski said. “What one person perceives as adequate fluids may not be sufficient.”

Nutritional counseling can help patients with symptoms such as abdominal pain, or conditions such as obesity, hypertension, or diabetes. Insurance coverage may be available to interested patients, who can find a local registered dietitian using the Academy’s website, eatright.org.

It takes time to help people understand how much fiber they eat, offer sustainable changes that are customized to include what they like, what they can afford, and their other health conditions, said Stefanski.

Over-the-Counter and Prescription Medications for Constipation

By the time a patient comes into the office, they have probably tried over-the-counter products on their own; it is wise to ask what they have tried, and for how long. The bigger issue, said Pasricha, is that patients often don’t distinguish between the mechanism of action of these agents, so they may not be using them strategically.

“The mistake people make is that they try one that doesn’t work, then they try something else, which doesn’t work, and when the third one doesn’t work, they say, nothing works!” Qureshi said. But that patient may need to be on all three products.

A patient may feel better using fiber supplements such as Metamucil or Citrucel, which help hold water in the stool and add bulk to it. People experiencing ongoing symptoms may benefit from adding an osmotic laxative (such as MiraLAX) or a stimulant laxative like bisacodyl (Dulcolax) or senna (Senokot).

For persistent problems, treatment with secretagogues such as linaclotide, plecanatide, and lubiprostone or other prescription medications may be helpful.

Tips for Patients

Qureshi tells physicians to ask their patients to be aware of their habits.

• They shouldn’t hold it. Busy people often postpone defecation, holding it when they feel the urge to go until they’ve finished work, but this teaches the body to ignore natural stimuli.
• They shouldn’t stay on the toilet for more than 3-5 minutes.
• They should sit on the toilet after breakfast. Eventually, the body will learn to go around the same time of the day.

Pasricha said, “Framing constipation as a whole-body issue (sleep, stress, movement, not just diet) resonates with patients in a way that a simple ‘eat more fiber’ directive doesn’t.”

Pasricha, Stefanski, and Qureshi reported having no conflicts of interest.