Magnesium citrate
"Today I went to the doctor due to some moderate/severe lower abdominal pain that wasn't going away after 2 days. It even woke me up in waves of shooting pain. An X ray showed that I constipation was in fact the root of my problem, so the doctor told me to go to the pharmacy and pick up a couple bottles of this stuff. I was already nauseous due to the constipation, so I only had about 3/4 of one bottle, and drank about 16oz or so of water. At first, not much happened, just occasional gas and nausea. About 4-5 hours later is when it really kicked in. And, it works very well. The nausea is going away too, I'm starting to get my appetite back, & I'm less bloated. Warning: when the tummy rumbles start, RUN do not walk to the nearest toilet."