Would Someone Please Explain This To Me?

I don’t understand how the federal government has the power to enact a law that makes recreational drugs illegal. Not being a lawyer or legal scholar, I just don’t get how this works. I guess lawyerly types use a different version of the English language than the rest of us do.

Specifically, here’s where I get confused. The U.S. Constitution enumerates the powers granted to the federal government. Rather than show my ignorance by attempting to interpret the Constitution, I’ll leave it to someone whom I think you will agree had a pretty good handle on the subject, Thomas Jefferson:

Resolved, That the Constitution of the United States, having delegated to Congress a power to punish treason, counterfeiting the securities and current coin of the United States, piracies, and felonies committed on the high seas, and offenses against the law of nations, and no other crimes, whatsoever; and it being true as a general principle, and one of the amendments to the Constitution having also declared, that “the powers not delegated to the United States by the Constitution, not prohibited by it to the States, are reserved to the States respectively, or to the people,”

(from The Kentucky Resolutions, 1798)

It sounds pretty unambiguous to me (in my state of blissful ignorance) that the federal government does not have the power to punish crimes involving so-called “controlled substances.” Clearly such crimes do not involve treason, counterfeiting, or piracy. Apparently those in power in 1919 agreed with this interpretation, since at that time a Constitutional amendment was required to criminalize a recreational drug.

But somehow 50 years later things had changed. And I say “things” because I’m not sure exactly what it was that changed. The Constitution didn’t change during that time, at least not in any relevant way. As far as I can tell, the only change is in how the Constitution was interpreted. You see, another power granted to the federal government by the Constitution is the power “To regulate Commerce with foreign Nations, and among the several States.” That power to regulate international and interstate commerce was interpreted as the power to regulate the use of recreational drugs. Again my ignorance shows, because to me “regulate” does not mean criminalize or punish. Regulate is something you do with legal commodities, and refers to things like taxation, importation, and distribution. As Mr. Jefferson pointed out, the federal government’s authority when it comes to punishing crimes is very limited.

Even so, let’s say for the sake of argument that the Controlled Substances Act of 1970 is legitimately based on the federal government’s power to regulate interstate commerce. How can such a law in any way, shape, or form apply to what I do in my own home? If I want to grow a medicinal herb in my home for my own personal use, medical or otherwise, and use said herb in private, where does the government get the authority to tell me I can’t? Not only that I can’t, but if I do I will be subject to arrest, prosecution, and imprisonment.

So would someone please explain to me how it is that the federal government has the power to tell consenting adults what they can or can’t do in the privacy of their own home? I just don’t get it.