Around 14% of adults in the US suffer from constipation. Females are more likely to develop constipation, which is generally defined as three or less bowel movements per week.

However, this is a theoretical definition — for some people, this may be the normal number of stools they pass each week and a reduction in this baseline number would be called constipation.

Nonetheless, constipation may be difficult to treat for some people. In other people, it may mean the presence of a serious underlying disorder. Many people turn to probiotics in such cases as opposed to laxatives, which are drugs doctors often prescribe for constipation.

If you’re wondering what the difference between the two is, this article will give you the answer.

What are laxatives?

Laxatives are medical drugs designed to relieve constipation. There are 4 main classes of laxatives used clinically and each works in a different way. Let’s take a look at how each class works and the side effects associated with it.

Osmotic laxatives
Osmotic laxatives include:

● Polyethylene glycol (PEG)
● Glycerin
● Magnesium hydroxide
● Magnesium citrate
● Lactulose
● Sorbitol

PEG is one of the most effective and well-tolerated laxatives out there, and many doctors consider it the best initial laxative to relieve constipation.

All osmotic laxatives work the same way — they pull water inside the gut from the arteries supplying it. As water content increases, this pushes on the wall of the gut, which triggers gut contractions. As gut contractions increase, you find it easier to poop.

But there are certain side effects associated with osmotic laxatives, which is why they should not be used without a doctor’s supervision. These include:

● Diarrhea
● Dehydration
● Ion imbalances in the blood, which can cause widespread symptoms

If used too much, osmotic laxatives may also cause unhealthy reductions in weight. This is why osmotic laxatives are often abused by people with bulimia nervosa, who counter weight gain caused by binge eating using laxatives.

Stimulant laxatives
Stimulant laxatives are also called secretory laxatives. These laxatives work by two major mechanisms — they increase colonic secretions and cause the colon to contract. Both of these help in easy passage of stools.

The two stimulant laxatives you may come across are senna and bisacodyl. Just like osmotics, side effects of these laxatives include diarrhea and ion imbalances — specifically, low potassium concentration in the blood.

Overuse of bisacodyl is also associated with a metabolic abnormality called alkalosis, where the pH of the blood gets too high. Long-term use of senna can lead to brown pigmentation of the colon, which is called melanosis coli.

For both of these reasons, stimulant laxatives are only appropriate for short-term constipation. You should not try to use them for long periods.

Stool softeners
Stool softeners like docusate integrate the fat and water content of the stool to make it softer. Softer stool is more likely to pass easily through the gut.

Side effects of docusate include diarrhea and abdominal discomfort (bloating and cramping).

Bulk-forming laxatives
This class of laxatives includes methylcellulose, psyllium husks, and polycarbophil. These are indigestible substances, which means they pass down all the way to the large intestine unchanged. Their main goal is to increase the bulk of the existing stool present in the gut.

As the stool becomes heavier, it’s more likely to exit the body. Some of these also increase the gut’s water content like osmotic laxatives.

Bulk-forming laxatives can cause bloating as a side effect. However, a more serious complication is ileus, which refers to a blockage in the intestinal tract. Because these laxatives are indigestible, they can obstruct the lining of the gut if not taken with adequate water.

If you’re taking bulk-forming laxatives and your constipation worsens instead of improving, report it to your doctor urgently.

How do probiotics differ from laxatives?

Probiotics differ from laxatives in a variety of ways, including how they work, how they’re used, and their effectiveness in constipation.

Unlike laxatives, probiotics target the gut microbiome to relieve constipation, which is a large colony of healthy bacteria that lives inside your gut. These bacteria are essential for the normal functioning of the gut and are thought to influence other areas of health as well.

The gut microbiome exists in a delicate balance and when alterations occur, bad bacteria can increase disproportionately, which can cause symptoms like diarrhea (or constipation).

Just like laxatives, probiotics can be used to relieve constipation. They do this by restoring the balance of the gut microbiome and improving bowel functioning.

However, research has shown probiotics to be effective for only certain conditions that cause constipation. This is why it’s unlikely that your doctor is going to prescribe you a probiotic supplement instead of laxatives.

Causes of constipation that have been shown to respond well to probiotics include:

● Irritable bowel syndrome (IBS)
● Childhood constipation
● Pregnancy-induced constipation
● Drug-induced constipation

But there are certain caveats you need to be aware of. One, there are many drugs that can cause constipation and probiotics have been shown to work against only two classes — chemotherapy drugs and iron supplements.

Other drugs that can lead to constipation include:

● Opioid analgesics
● Antacids
● Anticholinergics
● Antidepressants (e.g., tricyclic antidepressants)
● Calcium channel blockers
● Bile acid resins
● NSAIDs
● Beta blockers
● Calcium supplements
● Antipsychotics

This list is not exhaustive. If you develop constipation after starting a new drug, the best thing to do is to consult your doctor, who may be able to give you an alternative drug.

Two, while most childhood constipation is functional (and nothing to worry about), genetic causes of constipation like Hirschsprung’s are not too uncommon. This is why it’s important to consult a doctor instead of going straight to probiotic supplements.

Finally, one important difference between laxatives and probiotics is regulation. Laxatives are medical drugs, which is why they are tightly regulated by the FDA. This is not the case with probiotics because they’re considered supplements.

This is why you should always purchase probiotics from a reputable company that is research-oriented and has medical professionals onboard. Otherwise, you may end up with a low-quality product. Sometimes, the supplement may not even contain what the label says!

Medically reviewed by Onikepe Adegbola, MD PhD