Bisacodyl
"NEVER AGAIN will I take this laxative. Took one at 2pm, and when nothing had happened at 8pm I took another two. Woke up at midnight with the worst cramps I have ever had - thought I needed to go to hospital. Have been to the loo three times so yes, it works but I would rather stay constipated than go through this excruciating pain ever again. Definitely not recommended and not even a warning from doctor or pharmacist that it causes this severe stomach pain."