Bubabuggy is right – it depends a lot on what the rest of your record looks like. Basically the less you challenge yourself and the less you succeed, the less competitive you are. Obviously, though, you could drive yourself insane worrying about that. The average student that gets into medical school takes at least 4 classes per semester and rarely takes a premed class at a community college. One exception to that (an easy semester, one class at a community college, etc.) isn’t too bad, but try to keep them from mounting up. One thing I always did as a premed when I felt like I needed to lighten my load one semester to make room for something else is to take an easy class to add in some more credit hours. Consider taking an easy class outside your major so that you can have something a little different that won’t take your knees out from under you.