I know of people who have had it prescribed medically for dealing with the pain and nausea and stressed caused by Chron's, but I don't believe it necessarily will do anything in terms of calming down the driving factors behing the disease. It certainly won't put you into remission if thats what you're asking.
I'm sure this post will be taken down very shortly, but technically marijuana is a legitimate medication in certain places (Canada!) and I would argue more so a medicine than an "illegal substance" period.... But meh, could be just me.