Bisacodyl
"This product is strong. I mean STRONG. I only use it as a last resort when other, gentler remedies fail. I never need to take more than one pill, even though the box suggests up to 3. And I only take it if I expect to be near a bathroom for the entirety of the next day, because the laxative effect lasts about 24 hours. I make sure to drink plenty of water (or one of those sports/electrolyte drinks) to avoid dehydration. The only side effect I've noticed is chills. Many of the pink "women's laxatives" contain the exact same active ingredient as Dulcolax, so if you're avoiding one, check the labels very carefully before you buy the other."