For the first two years, it's easily doable for some people. I had classmates who averaged less than 30 hours a week of studying and did fine. But some people need to spend two or three times that much time just to pass.
It's pretty much impossible for most of third and parts of fourth year. There are times where you'll be in the hospital for 80+ hours a week. On top of not getting enough sleep, you might go all day without a chance to eat.