Osmotic laxatives draw water into the bowel from the intestines, thereby softening the stool. They can deplete electrolytes and cause dehydration, and so it’s also important to stay hydrated when taking them. They can work within six hours. Many are polyethylene glycol–based (Lax-A-Day, MiraLAX, PegaLAX, RestoraLAX). Unlike bulk-forming laxatives, osmotic laxatives are intended for short-term, not daily, use, they shouldn’t be taken for more than seven days, and they are habit-forming.
