(VNF) - The obvious culprits cause constipation including a low fiber diet, repeatedly ignoring the urge to go, not drinking enough water, or a lack of exercise. But constipation also has other, less-well-known causes, including certain medications and supplements, as well as potentially serious medical conditions.

Here are 13 possible causes of constipation you may not have considered.

Hypothyroidism

Hypothyroidism, or an underactive thyroid gland, slows the body’s metabolic processes—even the gut.

Not everyone with an underactive thyroid has constipation, nor do all cases of constipation mean that the butterfly-shaped gland in your neck is underperforming.

Still, "when I see a young person who’s constipated more than normal and really complaining, I do tend to get a thyroid level," says Carla H. Ginsburg, MD, assistant professor of medicine at Harvard Medical School in Boston.

Painkillers

Painkillers, specifically narcotics, can cause constipation.

"A lot of receptors for the narcotic class of drugs are in the digestive tract, so it tends to bring everything to a halt," says Thomas Park, MD, a gastroenterologist with the University of Rochester Medical Center Park in New York. "In general, it’s a good idea for everyone who’s placed on one of these drugs to also place them on a gentle laxative like a stool softener."

Some studies (but not all) have suggested that there might be a higher risk of constipation for people who are chronic users of pain relievers like aspirin and ibuprofen.

Chocolate

There’s some evidence that chocolate can cause constipation, though other studies show chocolate may actually help some people, Dr. Park says.

In one 2005 study, people with chronic constipation or irritable bowel syndrome were more likely than people without those problems to say that chocolate caused constipation (as did bananas and black tea).

Eliminate or cut back on chocolate if you think it could be causing your constipation.

Vitamins

Vitamins in general won’t cause constipation, but certain components, such as calcium and iron, can be a problem.

"I would tell a patient to stop taking the iron [or calcium] unless they really need it and, if they do need it, I would put them on a stool softener to counteract that," says Dr. Ginsburg, who is a spokesperson for the American Gastroenterological Association.

Laxative overuse

Some laxatives work by stimulating bowel activity. Such stimulant laxatives should be taken only as directed.

If used for long periods of time, stimulant laxatives can lead to dependence, meaning your body simply won’t function properly without them.

Stimulant laxatives include Dulcolax, Ex-Lax, Senna, and others.

Don’t take any medication—including laxatives—for longer than instructed by either the product’s label or your doctor.

Too much dairy

A diet high in cheese and other low-fiber/high-fat foods such as eggs and meat can slow down your digestion. Cut down on your intake of such foods, and increase fiber intake to 20 to 35 grams a day.

"If you’re going to have cheeses and red meat and eggs, mix in some salads or other foods that have fiber," Dr. Park advises. And avoid fast foods and processed foods, which are generally low in fiber.

Antidepressants

Constipation can be associated with selective serotonin reuptake inhibitor (SSRI) antidepressants such as Prozac (fluoxetine).

However, constipation is more of a problem with older tricyclic antidepressants such as Elavil (amitriptyline), says Dr. Park. Why any of these drugs have this effect isn’t clear, though.

If you’re taking an antidepressant and have this side effect, think about using a gentle stool softener.

Depression

Ironically, the very condition that antidepressants are meant to treat—depression—can also cause constipation.

Like hypothyroidism, depression causes a general slowdown of the body’s normal processes, which can also affect the bowel.

People with irritable bowel syndrome, which can be closely linked to depression, are also prone to constipation, Dr. Park says.

Antacids

Antacids are great for fighting heartburn, but some can cause constipation, particularly those containing calcium or aluminum, Dr. Park says.

Fortunately, the drugstore aisles are crammed with options, so if one medication is a problem you can try something else.

You can also cut down on your risk of heartburn by not overstuffing at meals. And consuming fewer fatty foods and more fiber will help prevent both problems.

Blood pressure and allergy meds

Constipation can be a side effect of some common drugs used to treat high blood pressure, such as calcium channel blockers and diuretics.

Diuretics, for instance, lower blood pressure by increasing urine output, which flushes water from your system. However, water is needed to keep stools soft and get them out of the body.

Antihistamines used to treat allergy symptoms can be a problem too.

Inflammatory bowel disease

Inflammatory bowel disease (IBD) includes two chronic conditions—Crohn's disease and ulcerative colitis. Both can cause cramping, weight loss, bloody stools, and other health problems.

Chronic diarrhea is a common symptom of both. However constipation can be a problem too.

In ulcerative colitis, constipation can be a sign of inflammation in the rectum and in Crohn's disease it can be a sign of an obstruction in the small intestine. However if you have constipation alone, without other symptoms, it's unlikely to be due to IBD.

Childbirth

Constipation is common during pregnancy, but childbirth itself can be a problem, possibly due to sluggish abdominal muscles or perhaps the use of pain relievers or an anesthetic during the delivery.

Also, "there may be some perineal soreness right after the delivery, so the fear of causing more discomfort may be an important factor in the constipation," says Dr. Park.

Although stretch injuries during childbirth can sometimes cause nerve damage that leads to constipation, this is less common.

Diabetes and neurological conditions

Diabetes can cause nerve damage that can affect a person’s ability to digest food, says Dr. Park.

Most people with advanced diabetes know they have it. Still, it’s reasonable to do a blood sugar test on someone who is regularly constipated, says Dr. Ginsburg.

Neurological conditions such as multiple sclerosis or Parkinson’s disease can cause constipation. Usually, though, "this goes with another symptom such as trouble urinating, double vision, or a gait problem," Dr. Ginsburg says./.

( Compiled by VNF )