How Do Laxatives Work?

What are PEG, Lactulose, Bisacodyl, and similar medications used for?

When dietary and behavioral changes are not enough to manage a child's constipation, a healthcare professional may recommend medication. The most commonly used medications for childhood constipation are laxatives, which help make bowel movements easier and more regular. They work in different ways and are classified into two main groups based on their mechanism of action: osmotic and stimulant laxatives. Below is a brief overview of how each agent works and its effectiveness in treatment. Multiple brand names are mentioned, as trade names vary by country.

Osmotic Laxatives

These medications help softening the stool and making it easier to pass. They are the first-line and most commonly used treatment group in children.

Polyethylene Glycol 3350 (PEG 3350) – Miralax®, Laxaday®, RestoraLAX®

PEG 3350 is a colorless, odorless, and tasteless powder that is mixed with a beverage. It is not absorbed by the intestine or bloodstream, does not cause dependency, and is safe for long-term use.

Polyethylene Glycol 4000 (PEG 4000) – DulcoSoft®

PEG 4000 works through the same mechanism as PEG 3350, with the only difference being a slightly higher molecular weight (4000 g/mol). Its clinical efficacy is comparable to PEG 3350, and some studies report better taste tolerability.

Lactulose – Duphalac®, Chronolac®, Lactulax®

Lactulose is a synthetic disaccharide that is broken down by gut bacteria, drawing water into the bowel. However, recent data show that it is not completely non-absorbed as previously believed and that its efficacy is lower compared to PEG. It may cause gas and bloating. Therefore, most current guidelines recommend it as a second-line option when PEG is unavailable.

Stimulant Laxatives

These agents stimulate intestinal muscles directly to help move stool through the colon. They are typically used for short-term relief or disimpaction (bowel clean-out) and are not recommended for long-term use.

Bisacodyl – Dulcolax®, Correctol®, Alophen®

Can be administered orally or rectally (as a suppository). When taken orally, it usually works within 6–12 hours, and when used rectally, within 15–60 minutes. It stimulates the colon mucosa, increasing peristalsis (bowel movements).

Senna (Sennosides) – Senokot®, Ex-Lax®, Fletcher's® Castoria

Senna is a natural plant-based stimulant laxative derived from Cassia angustifolia. Its active compounds, sennosides, stimulate the colon muscles and enhance mucosal secretion. It usually takes effect within 6–10 hours. Possible side effects include abdominal cramps and darkened stool color.

It is very important that these medications are used under the guidance of a healthcare provider. They will determine the right type of laxative and the correct dose for your child based on their age, weight, and the severity of their constipation.