Someone in a terminal condition who requests "more" pain relief has always been something that doctors encounter. Many times every day, the doctor will "help" them in that manner. That's just how the end of life works. The Oregon statute just makes it possible for patients to control this aspect of end-of-life care on their own terms.
If you find the law offensive, you can:
-Lobby in Oregon for a new ballot measure to overturn the law
-Not use the law yourself
I just don't see how federal power enters into this at all, unless you are comfortable with a massive over-reach of federal authority via the commerce clause, against state's rights.
In this particular case, as I've said, either the whole interpretation of the commerce clause goes (which I don't think likely) or the Oregon law goes.