Medications That Can Cause Constipation — and What You Can Do About It

If you've started a new medication and you've noticed pooping has become harder, it may not be a coincidence. Several widely used prescription and over-the-counter (OTC) medicines, as well as some supplements, can cause constipation.

“Constipation is one of the most common GI [gastrointestinal] symptoms people complain about, and it’s not uncommon for it to be related to a medication someone is taking,” says Mark Benson, MD, an associate professor of medicine and gastroenterologist at UW Health in Madison, Wisconsin.

Knowing which medicines may cause constipation can help you spot the connection and talk with your doctor about ways to manage the issue.

Several common drug classes are known to slow the digestive tract or otherwise make regular bowel movements more difficult, says Dr. Benson.

Opioid Pain Relievers

Opioids are prescription pain relievers used for moderate to severe pain. Examples include oxycodone, hydrocodone, morphine, and fentanyl. “Opioids are probably the most common prescription medications that cause constipation,” says Benson.

Blood Pressure Medications

Calcium channel blockers are used to lower blood pressure. Verapamil is one that can be particularly constipating, says Benson.

“Calcium channel blockers decrease calcium entry into some of the smooth muscle cells of the GI tract, and as a result, they decrease colonic motility,” he says. In other words, they can slow the contractions that push stool through the colon.

Antidepressants

Anticholinergics for Overactive Bladder and Other Problems

Anticholinergic drugs treat conditions including overactive bladder and some neurologic or gastrointestinal problems.

“These medications block a chemical called acetylcholine, and acetylcholine helps with gut motility. If you block that, it decreases gut motility, which leads to constipation,” says Benson.

Oxybutynin, a medication for overactive bladder, is one example of an anticholinergic that can cause constipation, says Sarah Rhodes, PharmD, an assistant professor of clinical science in High Point University’s Fred Wilson School of Pharmacy in North Carolina.

Ondansetron (Zofran) for Nausea and Vomiting

“If it’s prescribed frequently, it can lead to constipation because it decreases motility,” Benson says.

It’s easy to overlook something you picked up at the drugstore as the source of side effects, but several common OTC medicines are linked with constipation.

Antihistamines and Cold Remedies

Some medicines used for allergy and cold symptoms can slow the bowel.

“Antihistamines like Benadryl have an anticholinergic effect, so they block acetylcholine, and that decreases gut motility,” Benson says.

Loratadine (Claritin) and cetirizine (Zyrtec) are also common antihistamines that can contribute to constipation, says Dr. Rhodes.

Iron and Calcium Supplements

“Iron supplements are commonly used to prevent or treat iron deficiency and are a frequent culprit” of constipation, says Rhodes.

The exact reason this happens isn’t entirely clear, says Benson. “Iron can irritate the digestive tract and appears to reduce water in stool, making it harder to pass,” he says.

Antacids

Antacids neutralize stomach acid to relieve heartburn. Those containing calcium or aluminum can cause constipation, says Rhodes.

That includes calcium carbonate, an ingredient in antacids such as Tums, which can decrease smooth muscle contractions in the colon, says Benson.

For medication-related constipation, there are a few daily habits that may offer relief.

• Eat more fiber. Aim for about 30 grams (g) of daily fiber from foods such as fruits, vegetables, whole grains, and beans, says Rhodes.
• Drink enough water to keep stool soft. Benson recommends drinking an extra glass of water or two in the morning to help combat dehydration and constipation.
• Exercise regularly. Prioritize daily movement, within your abilities, says Rhodes.
• Use a footstool after meals. Bowel reflexes to help you poop tend to be strongest during these times, says Rhodes. You can use a footstool to raise your feet, which may make stool easier to pass, she says.

If those changes aren’t enough, supplemental fiber, such as psyllium or an osmotic laxative, such as polyethylene glycol (Miralax), may help, says Benson.

“Over-the-counter medications may be useful in managing constipation caused by short courses of medication, but always discuss them with your pharmacist or doctor first to make sure you’re choosing an appropriate option,” says Rhodes.

If you notice constipation shortly after starting a new medication, it could be due to the drug, says Benson.

But don’t make that diagnosis on your own, he says. “Always reach out to your prescribing doctor before stopping a prescribed medication,” says Benson.

Your healthcare practitioner may be able to tweak the dose or get you to a therapeutic dose more slowly to help limit constipation, says Rhodes.

Another option is to change your medication, she says. “Some drugs in the same class have different side-effect profiles, so your provider may also change you to one with less potential for constipation,” says Rhodes.

Rhodes recommends contacting your healthcare professional if you have any of the following.

• Constipation that lasts more than two weeks
• The need to use laxatives every day to have a bowel movement
• Constipation that doesn’t improve with dietary or supplemental fiber
• Abdominal pain or cramping
• Nausea or vomiting
• Blood in your stool or dark, tarry stool