MiraLAX Safety During Pregnancy
MiraLAX (polyethylene glycol 3350) is safe to use during pregnancy and is recommended by the American Gastroenterological Association as a first-line treatment for constipation in pregnant women. 1
Primary Evidence Supporting Safety
The American Gastroenterological Association explicitly recommends polyethylene glycol-based laxatives as safe treatment options for constipation during pregnancy, based on lack of systemic absorption and extensive clinical experience. 1
Polyethylene glycol works as an osmotic laxative by retaining water in the stool, and because it is not systemically absorbed, it poses minimal risk to the developing fetus. 1
Constipation affects 20-40% of pregnant women due to hormonal changes and physiological alterations, making effective treatment essential. 1
FDA Labeling Considerations
The FDA classifies polyethylene glycol 3350 as Pregnancy Category C, meaning animal reproductive studies have not been performed and it is not known whether it can cause fetal harm. 2
However, the FDA label states it "should only be administered to a pregnant woman if clearly needed," which reflects the lack of formal animal studies rather than evidence of harm. 2
The guideline evidence supersedes this conservative FDA labeling, as clinical experience demonstrates safety. 1
Contrasting Evidence on Safety Data
One hepatology guideline from 2021 states that "the safety of polyethylene glycol has not been adequately studied in pregnancy" in the context of bowel preparation for lower endoscopy. 3
This statement is outdated and contradicted by the 2025-2026 gastroenterology guidelines that explicitly endorse polyethylene glycol as safe based on extensive clinical use. 1
A 2020 randomized controlled trial in 113 pregnant women demonstrated that polyethylene glycol 4000 was both safe and effective for treating constipation during pregnancy, with no adverse drug reactions reported. 4
Treatment Algorithm
First-line approach: 1
- Increase dietary fiber to approximately 30 g/day with adequate fluid intake
- Ensure adequate hydration and regular physical activity
Second-line approach when dietary measures fail: 1
- Initiate polyethylene glycol (MiraLAX/Movicol) as an osmotic laxative
- Alternative: lactulose (also safe but may work more slowly than polyethylene glycol) 4
Dosing: 2
- Dissolve in 4-8 ounces of water, juice, soda, coffee, or tea
- Standard adult dose is 17 g daily, though the 2020 study used 10 g twice daily with good results 4
- May require 2-4 days to produce a bowel movement 2
Important Caveats
Excessive use can cause maternal bloating, though this is a tolerability concern rather than a safety issue. 1
If unusual cramps, bloating, or diarrhea occur, reduce the dose or discontinue temporarily. 2
Avoid prolonged use beyond 2 weeks without physician guidance, as chronic laxative use may result in electrolyte imbalance and dependence. 2
Bulk-forming agents (psyllium, methylcellulose) are also safe alternatives due to lack of systemic absorption and may be used concurrently. 1
Avoid straining during bowel movements by ensuring adequate time and using relaxation techniques. 1