Amendment IX
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
Amendment X
The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.
Conservatives typically don't endorse New Deal-era interpretations of the Commerce Clause . . .
Well, since MJ and every other illegal drug are regularly transported interstate for distribution, it's not much of a stretch at all.
Oh, and 9A doesn't imply that every human activity is a right, only that there are other rights not mentioned by the Constitution. Not excluding isn't the same as including.