Citizens don't have to point out some provision in the Constitution that allows them to do what they want, the Government has to point out some provision in the Constitution where it is given the specific authority to prevent you from doing what you want.
Where in the Constitution does it say the Federal Government has the right to keep me from enriching my own uranium, or constructing my own nuclear reactor.
Libertarian absolutist argument bore the hell out of me.
When the drug effects volition, legislation and discrimination of that drug is appropriate.
Expressed another way, if the drug causes harm and its use causes addiction, such that a person is no longer has liberty to decide not to take the drug, then removing restraint from its access condones the removal of liberty.