I'm finding that it fits together pretty well, but it may depend on the school. I go to a really small private school in the middle of nowhere, so they're a lot more informal than a big state school is likely to be. My roommate this year was a psych major, whereas I was psych + premed and I had quite a bit more work than her, but I wasn't dying from an overload or anything. A helpful thing that my academic advisor talked to me about was pushing all my non-MCAT-related classes to my senior year after I take the MCAT. That way, instead of taking english and electives before the MCAT, I can spend more time learning what I need to for the MCAT and spend my senior year taking pretty much all of my humanities classes and working on my senior thesis.