I was told it's used to help thicken the stool and slow down bowel movements. 

Imodium slows the gut and increases anal sphincter tone. It seems to work fine for J-pouchers. I personally get better results with Lomotil, though. 

My son has a J-pouch and has backed off from 12 immodium per day after surgery, down to 2.  It definitely helps control the flow, especially when sleeping, in school all day, etc.

Immodium works for J-pouchers. It works differently than lomotil. I think that I built up a tolerance for lomotil and it doesn't work as well for me. Immodium seems to stay as effective at the same dose.

You need a new doctor! It is not just for people with a colon, in fact I never took it before I had mine removed but now that I have a J pouch I could not survive without it!! Either he does not know what he is talking about or he is trying to steer you away from it because people who don't need it are abusing it to get high and for opiate withdrawls. But I would definitely not listen to him and at least talk to another Dr an find a dosage that works for you if needed.

Oh and for me Lomotil stops the feeling of having to go but Imodium slows the actual go.

Helps my husband...

It works great for me. I take 2 per day, rarely more. Have been doing that for over a year.

Btw, if you've been taking Immodium for a while, don't stop it suddenly. Taper off slowly instead, if you want to stop for some reason. Otherwise, you risk withdrawal symptoms -- kind of flu-like.