Depends on the non-med person IMO. If s/he is very laid back and can deal with the crazy schedules, the time dedicated to studying, the obsession with med-talk, the fact that most of your friends will probably be other med people, etc. It will be fine. I didn't really find it any more stressful than dating anyone else that had a busy lifestyle.
Then again, if the non-med person is a real stickler for schedules/planning, needs lots of down time with the SO and has no sympathy for the med profession, that relationship is doomed IMO.