MiraLAX generally takes about 12 to 24 hours to start working, but in some cases, it can take up to 96 hours (4 days) for a bowel movement to occur. Typically, it produces a bowel movement within 1 to 3 days after taking the dose. The timing depends on factors such as dosage, severity and cause of constipation, existing medical conditions, and individual digestion speed. MiraLAX works by drawing water into the colon to soften the stool, making it easier to pass, but it does not cause immediate stimulation of the intestines like some other laxatives. For bowel preparation before a colonoscopy, it may act faster (within a few hours). To increase effectiveness, it is recommended to follow dosage instructions, mix the powder with liquid, stay hydrated, and possibly take it in the morning to have a same-day effect. If constipation persists beyond 7 days or MiraLAX does not produce a bowel movement within 3 days, consulting a healthcare provider is advised. In summary, expect a bowel movement usually between 12 hours and 3 days after taking MiraLAX, with some variability based on individual factors.