constipation
"I used to use this medication whenever I was constipated and was okay.  However on one occasion I had a very nasty side effect, I vomited violently, had terrible cramping pain and was screaming in agony.  It was as bad as labour!  I won't go into too much detail regarding the terrible amount that passed out of me, but vomiting and the runs is not nice at all.  I have never had this side effect with another laxative and will never use it again.  I believe it is unpredictable - because I used it previously and nothing terrible happened - but I literally thought I was dying when I had that horrid experience.  If it happens to you I hope you drank lots of water afterwards.  I felt really ill and weak.  I should've reported this sooner!"