I'm pretty sure the graduate NSF grants are only for non-biomedical research. I do know one MD/PhD student who has NSF funding - he applied for and won an NSF grant when he thought he was going to do a PhD, went off to do a Marshall, and then decided to go MD/PhD when he came back to the States (and got very lucky that they didn't take the funding away from him). But other than getting one through a strange loophole like this, I don't believe NSF grants go to researchers in the medical sciences.