Bisacodyl
"I took the tablet as I had been constipated for around 2 weeks!!! Just over 2 hours since I had taken the tablet I felt very weak and sick, I felt as if I was about to throw up. Then the cramps started, they were horrific. Worse than anything I had ever felt before. It was as if I was getting punched from the inside (100x worse than any period pains I've experienced) and it lasted about an hour!!!! They did in the end relieve my constipation and the pains did stop but I will never take these tablets ever again, it was not worth going through all the pain."