Hi Aideen, sorry that I didn't see this until now. I'm not an expert, so take this with a grain of salt, but the typical agreed-upon dosage amount for LDN is 4.5mg, once per day. I took a quick look at the Contrave website, and it looks like the naltrexone is an 8mg dose in an extended-release capsule format. That's certainly a lower dose than normal naltrexone (standard doses for generic naltrexone HCl are 50mg pills), but I'm not sure whether 8mg would have the same effects as traditional LDN.
My guess: I don't think that it will hurt anything, but I don't know that it will have a tangible effect on your Crohn's.
Hopefully someone else can chime in that has a little bit more knowledge on the subject.