Yes, congress does have that power, BUT, they have passed and enforced laws that go VERY VERY VERY VERY VERY far beyond merely regulating the interstate commerce of dope.
Yeah, but it's related. If some kind of in-state activity has a substantial effect on the interstate commerce that Congress is constitutionally regulating, Congress has the power, under the Necessary and Proper Clause, to pass legislation controlling that activity.
Congress regulates interstate airlines. Even though a private pilot is flying from one part of his state to another, Congress may also regulate his activities if they interfere with interstate airline traffic.
Of do you trhink they're not allowed to do that?