Hop-Head or Dying Patient?

From msnbc: Dying woman rebuffed on medical marijuana - California appeals court rules against mother suffering brain tumor.

This is really a case I don't get. This woman is dying slowly of a brain tumour. She has a family that she still needs to look after, and her doctor says that medicinal marijuana is far and away the best treatment for her because it not only eases the pain but also boosts her otherwise nonexistant appetite, thus helping to keep her healthy. Unless the doctor is known to be crooked and bending the truth, that's a pretty darn good reason to let her use the stuff.

The judiciary, however, feels she can't break federal anti-drug laws. She will keep on using marijuana anyway.

This brings up the question: What makes some drugs okay and others not okay? Americans are among the most medicated people on the planet. They have drugs for everything down there, and everybody is taking something for some real or perceived ailment. This is a woman with a very real problem and a very real drug-based solution, yet the feds are giving her a hard time simply because the prescribed drug is "evil"? Doesn't make sense to me.