In my personal opinion, I think being a biochemistry major helps a lot. A lot of my classes, most of the biochemistry majors took in undergrad so they had a head start. In addition, a lot of drugs target certain biochemical pathways and other drugs, like certain antibiotics work on DNA gyrase, work on mRNA, and etc. The curriculum comitte at USC has been thinking about making an entire year (instead of one quarter or semister) of biochemistry as a prerequiste. I would also add having lab helps a little when they start talking about some of the biochemical techniques in class like western blot, sds page, southern blot, and etc.