Hi Rita, I don't use Metmucil no more, I use natural bulk Psyllium husk, the active ingredient in Metamucil, but much more cheaper, most health food stores will sell this. No problems with cramping. I take 1-2 tbsp every night before bedtime. Keeps me very regular, I also eat lots of low-carb veggies and berries, I also walk/jog everyday and drink lots of water during the day which will help with constipation. You don't want to use those chemical laxatives, they'll do more harm then good to your intestines if you take them on a regular basis.
Doreen has written a very good article on contipation here at this page. You might want to read it.

http://www.lowcarb.ca/tips/tips012.html

Christine