I never heard of prederm but senna is a natural laxative. Are you sure the doc didn't say Perdiem? I have seen it next to the Metamucil and Citrucel at the store, and I am pretty sure it has senna in it.
I almost tried it myself but the senna stopped me. I once drank a "laxative tea" with a bunch of herbs including senna and did it clean me out! yikes! I don't know if it was the senna that did it, but I just stick with plain, nonsweetened ground psyllium from the health food store when I need a dose of extra fiber. Kind of tastes like dirt but it works better for me than the Metamucil did.
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