Catherine Saint Louis voices alarm about Miralax, a common oral laxative made for adults but commonly prescribed to children to treat constipation:

The Food and Drug Administration has raised new questions about the safety of an adult laxative routinely given to constipated children, sometimes daily for years.

The agency has asked a team of scientists in Philadelphia to look more closely at the active ingredient in Miralax and similar generic products, called polyethylene glycol 3350, or PEG 3350.


Chronic constipation is common in children. Pediatricians and gastroenterologists initially attempt to treat it by making some dietary interventions: more fiber with natural juicy fruits and green, leafy vegetables, less processed foods, less calcium-binding fat (like in whole milk and cheese), and more water. These dietary changes, along with a couple of other “tricks-up-our-sleeves,” are still not enough to help some children have comfortable stools with any regularity. Pediatrician Natasha Burgert explains where Miralax comes in:

Miralax® has been used in the fight against chronic constipation in children of all ages for years. The active ingredient in Miralax® is polyethylene glycol 3350 (PEG 3350). PEG 3350 is a very large polymer that is too big to be absorbed by the intestine. When PEG 3350 is consumed, it stays in the gut and holds water. This makes the poop within the gut soft and easy to pass, gently relieving constipation. PEG 3350 does not work on the muscles or nerves of the gut so it not habit forming, nor does it cause a dependance on the product.


Here’s the problem. In 2008, the FDA detected two byproducts of PEG 3350 — ethylene glycol (EG) and diethylene glycol (DEG), both ingredients found in antifreeze, ink pens, toothpaste, cosmetics, and medications — in minute quantities in eight separate batches of Miralax. Dr. Burgert says tiny amounts shouldn’t cause concern:

Trace amounts of EG and DEG can be safely eliminated from your body. The chemicals are changed to metabolites in the liver and eliminated via your kidneys. (In other words, you pee it out.) However, large amounts of these chemicals are clearly unsafe and known to be toxic to humans and animals.


The “Precautionary Principle” applies in this case, putting the burden on the manufacturer of Miralax (Merck) and the FDA to demonstrate safety in children and produce new research to support its continued use. Like many medications used in the pediatric population, Miralax is not FDA-approved for use in children. In the meantime, Dr. Burgert will continue to use Miralax carefully, in judicious doses, for her pediatric patients:

With what is currently known, I have no reservations about my patients with severe constipation continuing to use the lowest-effective dose of Miralax® as part of their treatment plan. Chronic constipation is a significant medical issue. For many children, behavior modification and dietary changes are simply not enough to create positive change, and Miralax® is critical to achieve comfort and success. It is important to understand that completely stopping Miralax® may lead to greater harm, as children with untreated constipation can develop significant problems like severe pain, blockages, and bleeding.