How does MiraLAX work?
Last updated September 3, 2026.
Osmotic physics, not chemistry: polyethylene glycol holds water in your bowel, making stool bigger and softer so the bowel pushes it out naturally - the NHS's description of the macrogol class. It is barely absorbed into the bloodstream. That separates it from stimulant laxatives (senna, bisacodyl), which prod the bowel wall chemically - faster, but crampy, and the class with lazy-bowel concerns on long use. The cost of gentle: speed - expect 1 to 2 days, not today. The make-or-break habit: dissolve the powder fully in a full glass of liquid and keep hydrating - the osmotic effect needs water to borrow. Pymander is a free AI doctor, 24/7 by text, and can help you build a constipation plan.
What to do
- Dissolve fully, drink fully: the water is part of the dose.
- Expect 1 to 2 days: plan ahead, not last-minute.
- Hydrate through the day: it borrows your body water.
- Still constipated after 3 days? Call: per the NHS timeline.
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