I see a lot of people talking about miralax, but not psyllium. Psyllium and Metamucil packaging to me is a distortion as they seem to focus on constipation. Truth is, they work to BALANCE so whether you experience constipation or chronic diarrhea (my problem) they offer balance to the stool generating bulk where needed and alleviating constipation. If a stool could be called both bulked and soft at the same time, that is what I get from these products.
I've had IBS for 30 years and KNOW that if I drink a dose of these daily I have little to no problems with my BMs. Admittedly, I'm lazy about drinking it b/c it's slimy and hard to get down - you have to MEAN IT and drink it swiftly with frequent stirrings followed by a full glass of liquid after.
At $10 bucks a canister, natural, sugar-free psyllium is a great, cheap friend to those of us suffering from GI problems. Metamucil is same (but I don't like the fake sugar they use). I only have GI problems when I don't use psyllium and/or I let my diet go to hell. Heavy on the cooked veggies is a good thing and makes up for a myriad of other food sins.

I've been noticing that when I only use psyllium for my fiber supplements that sometimes my stools becoming too bulky. I started balancing it with methyl cellulose (citrucel) and that seems to help quite a bit.