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Diarrhea in Adults


Jonathan Gotfried

, MD, Lewis Katz School of Medicine at Temple University

Last full review/revision Mar 2020| Content last modified Mar 2020

Diarrhea is an increase in the volume, wateriness, or frequency of bowel movements. (See also Diarrhea in Children.)

The frequency of bowel movements alone is not the defining feature of diarrhea. Some people normally move their bowels 3 to 5 times a day. People who eat large amounts of vegetable fiber may produce more than a pound (1/2 kilogram) of stool a day, but the stool in such cases is well formed and not watery. Diarrhea is often accompanied by gas, cramping, an urgency to defecate, and, if the diarrhea is caused by an infectious organism or a toxic substance, nausea and vomiting.


Diarrhea can lead to dehydration and a loss of electrolytes, such as sodium, potassium, magnesium, chloride, and bicarbonate, from the blood. If large amounts of fluid and electrolytes are lost, the person feels weak, and blood pressure can drop enough to cause fainting (syncope), heart rhythm abnormalities (arrhythmias), and other serious disorders. At particular risk are the very young, the very old, the debilitated, and people with very severe diarrhea.

Causes of Diarrhea

There are many different causes of diarrhea, depending on how long the diarrhea has lasted (see Table: Some Causes and Features of Diarrhea).

The most common causes of acute diarrhea (lasting less than a week) are

The most common causes of chronic diarrhea (lasting more than 4 weeks) are

Diarrhea that has been present for more than 4 weeks may be a lingering case of acute diarrhea or the early stage of a disorder that causes chronic diarrhea.


Normally, stool is 60 to 90% water. Diarrhea occurs when not enough water is removed from the stool, making the stool loose and poorly formed. Stool may contain too much water if it

  • Passes too quickly through the digestive tract
  • Contains certain substances that prevent the large intestine from absorbing water
  • Contains excess water secreted by the intestines

Rapid passage (transit) of stool is a common cause of diarrhea. For stool to have normal consistency, it must remain in the large intestine for a certain amount of time. Stool that leaves the large intestine too quickly is watery. Many medical conditions and treatments can decrease the amount of time that stool stays in the large intestine. These conditions include an overactive thyroid (hyperthyroidism); Zollinger-Ellison syndrome (a condition of over-production of acid by a tumor); surgical removal of part of the stomach, small intestine, or large intestine; surgical bypass of part of the intestine; inflammatory bowel disease (such as ulcerative colitis); surgical removal of the gallbladder (cholecystectomy); and use of drugs such as antacids containing magnesium, laxatives, prostaglandins, serotonin, and even caffeine. Many foods, especially those that are acidic or have a very high amount of sugar (such as waffle or maple syrup), can increase the rate of transit. Some people are intolerant of specific foods and always develop diarrhea after eating them. Stress and anxiety are also common causes.

Osmotic diarrhea occurs when certain substances that cannot be absorbed through the colon wall remain in the intestine. These substances cause excessive amounts of water to remain in the stool, leading to diarrhea. Certain foods (such as some fruits and beans) and sugar substitutes in dietetic foods, candy, and chewing gum (for example, hexitols, sorbitol, and mannitol) can cause osmotic diarrhea. Also, lactase deficiency can lead to osmotic diarrhea. Lactase is an enzyme normally found in the small intestine that converts lactose (milk sugar) to glucose and galactose, so that it can be absorbed into the bloodstream. When people with lactase deficiency drink milk or eat dairy products, lactose is not digested. As lactose accumulates in the intestine, it causes osmotic diarrhea—a condition known as lactose intolerance. The severity of osmotic diarrhea depends on how much of the osmotic substance is consumed. Diarrhea stops soon after the person stops eating or drinking the substance. Blood in the digestive tract also acts as an osmotic agent and results in black, tarry stools (melena). Another cause of osmotic diarrhea is an overgrowth of normal intestinal bacteria or the growth of bacteria normally not found in the intestines. Antibiotics can cause osmotic diarrhea by destroying the normal intestinal bacteria.

Secretory diarrhea occurs when the small and large intestines secrete salts (especially sodium chloride) and water into the stool. Certain toxins—such as the toxin produced by a cholera infection or during some viral infections—can cause these secretions. Infections by certain bacteria (for example, Campylobacter) and parasites (for example, Cryptosporidium) can also stimulate secretions. The diarrhea can be massive—more than a quart (1 liter) of stool an hour in cholera. Other substances that cause salt and water secretion include certain laxatives, such as castor oil, and bile acids (which may build up after surgery to remove part of the small intestine). Certain rare tumors—such as carcinoid, gastrinoma, and vipoma—also can cause secretory diarrhea, as can some polyps.

Inflammatory diarrhea occurs when the lining of the large intestine becomes inflamed, ulcerated, or engorged and releases proteins, blood, mucus, and other fluids, which increase the bulk and fluid content of the stool. This type of diarrhea can be caused by many diseases, including ulcerative colitis, Crohn disease, tuberculosis, and cancers such as lymphoma and adenocarcinoma. When the lining of the rectum is affected, people often feel an urgent need to move their bowels and have frequent bowel movements because the inflamed rectum is more sensitive to expansion (distention) by stool.

Diarrhea caused by malabsorption is characterized by oil or grease in the stool and an oily rim around the toilet bowl after stool is flushed. Malabsorption of bile salts, which can result from certain disorders, can cause diarrhea by stimulating water and electrolyte secretion; the stools have a green or orange color.

Foods and Beverages That Can Cause Diarrhea

Food or Beverage

Ingredient Causing Diarrhea

Sugar-free gum, mints, sweet cherries, or prunes

Hexitols, sorbitol, or mannitol

Apple juice, pear juice, grapes, honey, dates, nuts, figs, soft drinks (especially fruit flavors), prunes, or waffle or maple syrup


Milk, ice cream, yogurt, or soft cheese


Coffee, tea, cola drinks, or some over-the-counter headache remedies


Certain fat-free potato chips or fat-free ice cream


Evaluation of Diarrhea

Not every episode of diarrhea requires immediate evaluation by a doctor. The following information can help people decide whether a doctor’s evaluation is needed and help them know what to expect during the evaluation.

Warning signs

Certain findings raise suspicion of a more serious cause of diarrhea.

  • Blood or pus in the stool
  • Fever
  • Signs of dehydration (such as decreased urination, lethargy or listlessness, extreme thirst, and a dry mouth)
  • Chronic diarrhea
  • Diarrhea at night
  • Weight loss

When to see a doctor

People who have warning signs of blood or pus in the stool, fever, or signs of dehydration should see a doctor right away, as should those with significant abdominal pain. Such people may need immediate testing, treatment, and sometimes admission to a hospital. If the only warning signs are chronic or nighttime diarrhea or weight loss, people should see a doctor within a week or so. People without warning signs should call a doctor if diarrhea lasts for more than 72 hours. Depending on the person's other symptoms, age, and medical history, the doctor may recommend the person have an examination or try at-home or over-the-counter treatments (see treatment of diarrhea).

What the doctor does

Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the diarrhea and the tests that may need to be done (see Table: Some Causes and Features of Diarrhea).

A doctor begins by asking how long the diarrhea has been going on and how severe it has been. Simultaneous occurrence of diarrhea in friends, family members, or other personal contacts is sought. Other important questions focus on

  • Circumstances around when it started (including recent travel, food ingested, and source of water)
  • Drug use (including any antibiotics within the previous 3 months)
  • Abdominal pain or vomiting
  • Frequency and timing of bowel movements
  • Changes in stool characteristics (for example, presence of blood, pus, oil or grease, or mucus and changes in color or consistency)
  • Changes in weight or appetite
  • Feeling an urgent need to defecate or to defecate constantly

The physical examination begins with the doctor's evaluation of the person's fluid and hydration status. A full examination of the abdomen is done, as is a digital rectal examination to check for the presence of blood.

Some Causes and Features of Diarrhea


Common Features*


Acute (less than 1 week)†

Gastroenteritis due to viruses, bacteria, or parasites‡

Often vomiting

Rarely fever or blood in stool

Little or no abdominal pain (except during vomiting)

Sometimes recent contact with infected people (such as those at a day care center, at a camp, or on a cruise), with animals at a petting zoo (where Escherichia [E.] coli may be acquired), or with reptiles (where Salmonella bacteria may be acquired)

Sometimes recent consumption of undercooked, contaminated food or contaminated water

A doctor’s examination

Sometimes examination and testing of stool

Food poisoning

Diarrhea that started suddenly, often with vomiting, within 4 to 8 hours of eating contaminated food

Often present in other people

Typically lasting 12 to 24 hours

A doctor’s examination

Side effects of drugs‡ (including antibiotics, many cancer chemotherapy drugs, colchicine, and quinine/quinidine)

Recent use of a drug that causes diarrhea

Often no other symptoms

A doctor’s examination

Sometimes tests for Clostridioides difficile (formerly Clostridium difficile) toxin in stool

Chronic (4 weeks or more)

Dietary factors such as

  • Intolerance of cow’s milk
  • Overeating of certain fruits or juices (such as pear, apple, or prune)

Diarrhea only after consuming a substance that could cause diarrhea

Abdominal bloating and passing of gas (flatulence)

Explosive diarrhea

A doctor’s examination

Sometimes a breath test to detect hydrogen, indicating undigested food

Examination and analysis of stool to check for unabsorbed carbohydrates

Irritable bowel syndrome

Intermittent diarrhea associated with abdominal pain

Often diarrhea alternating with constipation

No bleeding, weight loss, or fever

Usually begins during the teens or 20s

Symptoms usually present for more than 12 weeks

Changes in the frequency of bowel movements or consistency of stool

A doctor’s examination

Sometimes blood tests and colonoscopy

Inflammatory bowel disease such as

Blood in stool, crampy abdominal pain, weight loss, and loss of appetite

Sometimes arthritis, rashes, sores in the mouth, and tears in the rectum



Stool tests

Malabsorption disorders such as

Light-colored, soft, bulky, and unusually foul-smelling stool that may appear oily

Abdominal bloating and flatulence

Weight loss

For tropical sprue, long-term (over 1 month) residence in a tropical country

For pancreatic insufficiency, usually in a person known to have a disorder of the pancreas (such as chronic pancreatitis or cystic fibrosis)

Tests to measure the amount of fat in stool samples collected over several days

If celiac disease is suspected, blood tests to measure the antibodies produced when people with celiac disease eat foods containing gluten

For celiac disease and tropical sprue, especially celiac disease, biopsy of the small intestine

Certain tumors

For colon cancer, sometimes blood in stool, decreased stool diameter, and weight loss

For endocrine tumors, various symptoms, including abdominal pain or cramping, flushing, and massive watery diarrhea

Blood tests



Often nervousness, trouble tolerating a hot environment, fatigue, palpitations, weight loss, and rapid heart rate

Blood tests

Surgery on the stomach or intestines (such as gastric bypass for weight loss or removal of a significant length of intestine)

Obvious recent surgery

A doctor’s examination

* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present.

† Diarrhea that has been present for 1 to 4 weeks may be a lingering case of acute diarrhea or the early stage of a disorder that causes chronic diarrhea.

‡ Certain infections and certain drugs can also cause chronic diarrhea.

CT = computed tomography; HIV = human immunodeficiency virus; MRI = magnetic resonance imaging.


The need for testing depends on what the doctor finds during the history and physical examination (see Table: Some Causes and Features of Diarrhea). Acute watery diarrhea (lasting less than about 4 days) without warning signs is usually caused by a viral infection, and people who otherwise appear well do not require testing. People with warning signs of dehydration, bloody stool, fever, or severe abdominal pain typically need testing—particularly those who are very young or very old. In these people, doctors do blood tests to detect blood and electrolyte abnormalities and stool tests to detect blood, markers of inflammation, and the presence of infectious organisms (such as Campylobacter, Yersinia, amebas, Giardia, and Cryptosporidium). Some causes of infection are detected by looking under the microscope, whereas others require a culture (growing the organism in the laboratory) or special enzyme tests (for example, Shigella or Giardia). If the person has taken antibiotics within the past 2 to 3 months, the doctor may test the stool for Clostridioides difficile (formerly Clostridium difficile) toxin. A colonoscopy is usually not necessary.

For diarrhea lasting more than 4 weeks (more than 1 to 3 weeks for people who have a weakened immune system or who appear seriously ill), similar tests are done. In addition, the doctor may test the stool, including tests for fat (indicating malabsorption) , do blood tests, and do a colonoscopy to examine the lining of the rectum and colon and to gather samples to test for infection. People whose symptoms seem related to diet may have a breath test to look for hydrogen, which suggests they are not absorbing carbohydrates. Sometimes a biopsy (removal of a tissue specimen for examination under a microscope) of the rectal lining is done to look for inflammatory bowel disease. Sometimes the volume of stool over a 24-hour period is determined. Imaging tests, such as computed tomography (CT) enterography, may be needed if the doctor suspects certain tumors. If doctors are still uncertain about the diagnosis, they may need to assess the function of the pancreas. Depending on the person's symptoms, doctors may also do tests for thyroid or adrenal gland disease.

Treatment of Diarrhea

Treatment is directed at the cause of diarrhea, when possible. For example, dietary and drug causes are avoided, tumors are removed, and drugs are given to eradicate a parasitic infection. However, in many cases, the body heals itself. A viral cause usually resolves by itself in 24 to 48 hours.


Extra fluids containing a balance of water, sugars, and salts are needed for people who are dehydrated. As long as the person is not vomiting excessively, these fluids can be given by mouth (see Dehydration : Treatment). Seriously ill people and those with significant electrolyte abnormalities require intravenous fluids and sometimes hospitalization.


Drugs that relax intestinal muscles and slow intestinal transit (antidiarrheal drugs) can help slow diarrhea. Loperamide is available over the counter. Opioid drugs, such as codeine, diphenoxylate, and paregoric (tincture of opium), are available by prescription and also can help. However, certain bacterial causes of gastroenteritis, particularly Salmonella, Shigella, and Clostridioides difficile, can be worsened by antidiarrheal drugs. Doctors typically recommend antidiarrheal drugs only for people with watery diarrhea and no warning signs because such people are unlikely to have such bacterial infections. Eluxadoline is another drug that may be given to some people who have diarrhea caused by IBS.

Over-the-counter drugs include adsorbents (for example, kaolin-pectin), which adhere to chemicals, toxins, and infectious organisms. Some adsorbents also help firm up the stool. Bismuth helps many people with diarrhea. It has a normal side effect of turning the stool black. Bulking agents used for chronic constipation, such as psyllium or methylcellulose, can sometimes help relieve chronic diarrhea as well.

Key Points about Diarrhea

  • In people with acute diarrhea, doctors examine the stool only if they suspect people have certain acute infections or if people have prolonged symptoms (that is, more than about 4 to 7 days) or warning signs.
  • Doctors avoid using antidiarrheal drugs if there is a possibility that the person has Clostridioides difficile, Salmonella, or Shigella.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Eluxadoline VIBERZI
colchicine COLCRYS
Loperamide IMODIUM
quinidine No US brand name

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