Gonzales v. Oregon
The Court said that Congress also never meant for the Controlled Substance Act to control medical practices.  The states had always had the right to control their own medical practices.  Ashcroft decided that he could create a meaning of "legitimate medical practice" that every state would have to follow.  The Court ruled that the Attorney General did not have this power to take away the states' rights to decide this for themselves.  Also, since he was not a medical expert, he should not be deciding what "legitimate medical practice" was.