No. Drug laws stem from international treaties. It's a complex, highly specific mission of the federal government, which is basically the definition of being suited for its own agency.
I don't think something being "a complex, highly specific mission of the federal government" necessarily means it needs it's own cabinet level position. Our nuclear triad is "a complex, highly specific mission of the federal government" yet it fits nicely into one branch of the DoD. I'm sure it wouldn't be hard to come up with several more examples.
and yes, it should be. And all drugs should be decriminalized. (not normal)