This has been interpreted as commerce from the point of origin within the state to its final destination within another. It does not, however, give Congress the power to regulate commerce that is entirely within one state.
BUT, if Congress IS regulating interstate commerce and some intrastate activity "substantially effects" Congress' interstate regulatory efforts, the Necessary and Proper Clause gives Congress the power to write laws covering that particular intrastate activity.
Think about it. Do you believe the Founding Fathers would give Congress the power to regulate interstate commerce, yet allow the individual states to undermine and subvert their regulatory efforts? Why give Congress the power to begin with?
As many a court have said, "this is not our domain". This is between the people and their elected representatives.
And I agree. If the people don't like the drug laws, don't like what Congress is doing with their authority, it is up to the people to remedy that, not the courts.