Importantly, there is nothing in the Constitution — by which, under Article 6, Section 2, officials at every level of government are obligated to abide — that authorizes the banning of any substance or enforcing that ban with the threat of injury, incarceration, or death. The lawful powers of the federal government are enumerated in Article 1, Section 8, and they do not include forbidding drugs or any other substance. Politicians early in the 20th century understood this, and passed a Constitutional amendment allowing them to outlaw alcohol. No such amendment has ever been passed, or even proposed, with regard to drugs.

"Some Random Thoughts About the War On Drugs"