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.
If you're going to take an originalist approach to the issue, it's abundantly clear that that power was listed in the Constitution so as to take it away from the states, not to give Congress any new powers. There isn't a scintilla of evidence from the writings of either federalists or anti-federalists at the time that the purpose of the clause was to give the federal government any restrictive power over actual commercial transactions within the country. And accordingly Congress never tried to exercise such a power until 100 years after the Constitution went into effect.
That's your current pet theory. Got anything to support it?