PureLax and MiraLAX are the same medication. Both contain polyethylene glycol 3350 at the same dose of 17 grams per capful, and they work identically in your body. PureLax is CVS Health’s store-brand version of MiraLAX, sold at a lower price point with packaging that explicitly states it compares to the active ingredient in MiraLAX.
What’s Actually in Each Product
Both PureLax and MiraLAX contain a single active ingredient: polyethylene glycol 3350, dosed at 17 grams per capful. There are no additional active compounds in either product. Neither contains inactive ingredients like flavorings or sweeteners in the unflavored versions, which makes the two products functionally interchangeable.
This isn’t a case where a generic has a “similar” ingredient. The molecule is identical. The FDA requires store-brand over-the-counter medications to contain the same active ingredient, in the same amount, in the same dosage form as the name brand they reference. PureLax meets all of those requirements.
How Polyethylene Glycol 3350 Works
Polyethylene glycol 3350 is an osmotic laxative, meaning it draws and holds water in your stool as it moves through the colon. The compound forms bonds with water molecules that prevent your intestines from reabsorbing that water the way they normally would. The result is softer, bulkier stool that’s easier to pass, along with more frequent bowel movements.
Because the medication is barely absorbed into your bloodstream, it stays in the digestive tract and acts locally. This is part of why it’s considered a first-line treatment for functional constipation in both adults and children. Stanford Medicine’s clinical guidelines recommend polyethylene glycol as the go-to therapy for constipation management.
How Long It Takes to Work
At the standard over-the-counter dose (17 grams once daily), most people notice results within one to three days of regular use. The medication is designed for gradual relief rather than immediate action, which is why the label directs you to use it daily for up to seven days.
At higher clinical doses used under medical supervision, the timeline compresses. A study published in the American Journal of Gastroenterology found that a larger dose produced a bowel movement in most subjects within about 15 hours, with complete evacuation reported after the second bowel movement. At the standard OTC dose, the effect is gentler and more predictable. No subjects in that study experienced cramping, diarrhea, or incontinence, and lab markers like electrolytes and kidney function remained unchanged.
Why the Price Differs
The only meaningful difference between PureLax and MiraLAX is cost. MiraLAX is a name brand manufactured by Bayer, while PureLax is CVS Health’s private-label equivalent. Name-brand pricing reflects marketing, brand recognition, and the original research investment. Once a product’s exclusivity period ends, any manufacturer can produce the same formulation and sell it for less.
You’ll find similar store-brand versions at nearly every major pharmacy and retailer. Walgreens, Walmart, and Target all sell their own polyethylene glycol 3350 powders with identical dosing. The only things that change are the label design and the price tag.
Dosing for Adults and Children
The standard adult dose is one capful (17 grams) dissolved in 4 to 8 ounces of any beverage, taken once daily. The powder dissolves completely and has no taste or grit in its unflavored form, which makes it easy to mix into water, juice, or coffee.
For children, dosing is weight-based rather than a standard capful. Kids one year and older typically receive 0.4 to 1 gram per kilogram of body weight per day for maintenance. Infants between 6 and 12 months use the same weight-based range. Because the math matters with small children, pediatric dosing is best guided by your child’s doctor, who can calculate the right amount and adjust it based on response.
What to Expect With Regular Use
Polyethylene glycol 3350 is well tolerated by most people. The most commonly reported issues are mild bloating, gas, and loose stools, all of which tend to settle as your body adjusts. Because the compound stays in your gut and doesn’t meaningfully enter your bloodstream, systemic side effects are rare.
The over-the-counter label recommends using it for no more than seven consecutive days without medical guidance. For people with chronic constipation, doctors frequently prescribe longer courses, sometimes weeks or months, with monitoring. The safety profile supports extended use when it’s clinically appropriate, but that decision belongs to a healthcare provider who knows your full picture.