Magnesium citrate
"I was very skeptical after going two hours without having to go to the bathroom after drinking an entire bottle of the lemon lime tasting one....
It was late at night so I decided to just go to bed and hope that I would go in the early am when I woke up....
(Previous to this, days before, I took so many other things that DIDN'T work... I was starting to get nervous that it was a more serious issue).....
Well..... I'm here to say that after not having a BM for over a week, I can definitely, DEFINITELY say this stuff works! 
It finally "kicked in" around 5 am.... which was 9 hours later... not painful... But be prepared to be in the bathroom awhile... So far, it's been on and off for about 45 minutes. I'm just happy it's working!!!"