What Are the Differences Between Dulcolax vs. Miralax?

Medically reviewed by Lindsay Cook, PharmD

Dulcolax (bisacodyl) and Miralax (polyethylene glycol 3350) are over-the-counter (OTC) medications used to treat constipation. Constipation is characterized by having fewer than three bowel movements a week or having hard or difficult-to-pass stool.

Dulcolax is a stimulant laxative that directly stimulates the colon's nerves, resulting in increased colonic motility and increased water content of stool.

Miralax is an osmotic laxative that is not absorbed from the gastrointestinal tract. It does not directly stimulate colonic smooth muscle but promotes water movement into the colon by osmosis. This intestinal distention then results in a bowel movement.

These laxatives differ in their time to produce a bowel movement. Dulcolax suppositories are the fastest, followed by Dulcolax tablets, and Miralax is the slowest. All are generally well-tolerated, with most side effects gastrointestinal in nature.

This article will discuss two common OTC laxatives used to treat constipation: Dulcolax and Miralax.

What Are the Main Differences Between Dulcolax and Miralax?

Dulcolax is the brand name for the OTC stimulant laxative containing the active ingredient bisacodyl. It’s important to note that Dulcolax is a brand of products, some of which contain other active ingredients (e.g., docusate, magnesium hydroxide) and do not contain bisacodyl. For this article, Dulcolax and bisacodyl are used interchangeably.

Bisacodyl works directly on the nerve plexus of smooth muscle in the intestines to stimulate colonic motility and increase stool's water content. It is available as an oral tablet or rectal suppository.

Miralax is an osmotic laxative that attracts water into the colon by osmosis. This increases colonic peristalsis (a type of contraction in the intestines), thereby promoting a bowel movement. It comes as a powder that needs to be mixed in 4 to 8 ounces of water or any beverage and then drank.

Both Dulcolax and Miralax are available as generic products. Bisacodyl suppositories produce a bowel movement the fastest (in 15 minutes to 1 hour), followed by bisacodyl tablets (6 to 12 hours), then Miralax (one to three days).

Dulcolax vs. Miralax: Uses

Dulcolax can be used by children ages 6 years and older up through adults. For children under 6, consult a healthcare provider.

Miralax’s manufacturer states that it can be used without a prescription by people 17 and older. Adolescents and children under 17 can use Miralax with guidance from a healthcare provider.

Many pediatric gastroenterologists recommend Miralax for treating constipation in children.

How Long Do Dulcolax and Miralax Take to Start Working?

Bisacodyl tablets generally produce a bowel movement 6 to 12 hours after administration.

Bisacodyl rectal suppositories work within 15 minutes to 1 hour.

Miralax typically produces a bowel movement in one to three days.

Dulcolax vs. Miralax: What Are the Side Effects?

Miralax’s side effects are gastrointestinal and may include nausea and loose, watery, or more frequent stools.

Dulcolax may cause abdominal discomfort, cramping, and diarrhea. Side effects of Dulcolax appear to be dose-related, with higher doses more likely to cause side effects.

Dosage: Dulcolax vs Miralax

This table summarizes the doses for the different formulations available for Dulcolax and Miralax.

Which Is More Effective?

Dulcolax and Miralax have not been directly compared to each other in clinical trials. Both are effective at treating constipation. Miralax is the OTC laxative with the most robust clinical evidence and is considered safe since it is not absorbed into the systemic circulation.

Dulcolax vs. Miralax: Which Is Right for Me?

When deciding which OTC laxative to use, consider how quickly you want it to work.

Dulcolax tablets are usually taken at bedtime with the goal of producing a bowel movement the next morning.

Sometimes, Miralax needs to be taken for several days before producing a bowel movement. And for those desiring almost immediate relief, Dulcolax suppositories can work 15 minutes to 1 hour after taking it.

You should also consider the ease of taking each of these medications. Miralax is tasteless and colorless when dissolved. It can also be mixed with any beverage, making it easy for children.

Dulcolax tablets have an enteric coating, so they must be swallowed whole without chewing or crushing, which may present an issue for young children. Some people may need assistance in administering the rectal suppository.

When taking a stimulant laxative like Dulcolax for the first time, consider starting with a low dose (5 mg) to see how your body reacts. In clinical trials, more people reported side effects when they took a higher dose of bisacodyl.

Related: Natural Constipation Remedies

Summary

Dulcolax and Miralax are both OTC laxatives used to treat constipation. Dulcolax is a stimulant laxative that works faster than Miralax.

While Dulcolax tablets produce a bowel movement in 6 to 12 hours, the suppositories work much faster, producing a bowel movement within 1 hour. Miralax is a powder that is mixed into a beverage and taken daily until it produces a bowel movement in one to three days.

Both are generally well-tolerated, with most side effects being gastrointestinal, such as loose stool or diarrhea.

Talk to a healthcare provider about how often you should use these laxatives. If constipation is an ongoing problem, you may need to work on addressing the underlying cause.

Frequently Asked Questions

Who shouldn’t use Dulcolax or Miralax?

Do not use Miralax if you are allergic to polyethylene glycol or have kidney disease. Do not take Dulcolax tablets if you cannot swallow them whole.

Can you take Dulcolax or Miralax every day?

Miralax’s manufacturer recommends using it for up to seven days, after which you should discuss further treatment with a healthcare provider.

While most data for the safety of Dulcolax is limited to four weeks of use, some experts believe it is safe to use two to three times per week (to produce two to three bowel movements per week) long-term without risk of dependence.

In general, you should discuss any sudden change in bowel habits that lasts more than two weeks with a healthcare provider.

Read the original article on Verywell Health.