Well, Metamucil and other fiber supplements have a completely different action and function than Imodium.
Imodium is a bowel slower. By slowing the gut, you absorb more water and nutrients, and the stool thickens by having increased time within the gut.
Fiber supplements add bulk and help thicken the stool. This makes it easier to retain and less painful to expel. But, it does NOT reduce your output. If anything, it increases it.
I was put on both Imodium and Metamucil while I was still in the hospital recovering from my surgery. I found that I was intolerant of Metamucil and it increased my intestinal gas. It did thicken my stool, but since I was not having continence issues, it was not helpful. I wound up visiting the toilet more. I did have better luck with Citrucel, which does not contain psyllium, but methylcellulose. Some people are just sensitive to psyllium. I guess I was one of them. The main thing with fiber supplements is that for our purpose (thickening rather than as a laxative) we do not drink a bunch of water with each dose. Just enough to dissolve it and get it down.
Jan