Magnesium citrate
"I had been so horribly backed up that I coild feel the skin on my stomach stretching. I tried taking herbal colon cleanse pills in hopes that it would help, but after 4 days of zero bowel movements I decided to turn to Magnesium Citrate. I took 10oz first thing in the morning on an empty stomach followed by a liter of water. 30 minutes later it kicked in. For about an hour and a half I also had nausea and stomach cramps. Once things started moving more it went away.  Like another reviewer said, this will make you pee out of your butt. If you are looking to be cleaned out and immediate constipation relief, I highly recommend this product."