We have similar products here to those in the US, but our's have different trade names, so I'm often unsure if we're talking about the same thing, but....

I was told never to take Metamucil, as it can have the opposite effect in an MSer, to that for a "normal" person.

For some reason it interferes with peristalsis in the bowel of the MSer, causing the bowel contents to come to a stand still rather than passing through.

I know that several people here successfully take Metamucil, and unfortunately I couldn't find the article I had that demonstrates what I was told, but just letting you know in case you fall into this group.