Yes, Polyethylene Glycol 3350 is the Active Ingredient in MiraLAX
Polyethylene glycol 3350 (PEG 3350) is indeed the active ingredient in MiraLAX, as confirmed by FDA labeling. 1
Product Identity and Formulation
- MiraLAX contains 17 grams of polyethylene glycol 3350 per dose, whether dispensed in bottle form (measured with a cap filled to the line) or in individual packets 1
- The FDA-approved labeling explicitly identifies "Polyethylene Glycol 3350" as the active ingredient in this over-the-counter osmotic laxative 1
Mechanism of Action
- PEG 3350 is a long-chain polymer of ethylene oxide that functions as an osmotic laxative by sequestering fluid in the bowel 2
- It increases the amount of water in the large bowel, either by drawing fluid from the body into the bowel or by retaining administered fluid 2
- The compound is an inert polymer that does not undergo significant systemic absorption 2
Clinical Evidence and Efficacy
- PEG 3350 at 17 grams daily is safe and effective for both short-term and chronic constipation treatment, with demonstrated efficacy extending up to 12 months without evidence of tachyphylaxis 3, 4
- In chronic constipation trials, 52% of PEG-treated patients achieved treatment success compared to 11% with placebo (p<0.001) over 6 months 3
- The response is durable over time, with 80-88% of patients reporting successful treatment across multiple months of observation 4
Safety Profile
- Laboratory monitoring shows no clinically significant changes in electrolytes, hematology, or blood chemistry even with chronic use up to 12 months 3, 4
- The most common adverse effects are mild-to-moderate gastrointestinal complaints including diarrhea, flatulence, and nausea, which are not significantly different from placebo in most studies 3, 5
- No cases of incontinence or severe cramping were reported even at higher doses (up to 85 grams) 6
Important Clinical Considerations
- The standard dose of 17 grams must be mixed with 8 ounces of liquid for proper administration 7
- Many treatment failures occur because patients do not mix PEG with sufficient liquid—this is a critical pitfall to avoid 7
- PEG 3350 is available over-the-counter in the United States and is widely used for occasional constipation, chronic idiopathic constipation, and irritable bowel syndrome with constipation 2