the U.S. government's treaty obligations preclude Colorado and Washington from legalizing marijuana. Responding to passage of Colorado's Amendment 64 and Washington's Initiative 502, "these developments are in violation of the international drug control treaties." That does not appear to be true, and even if it were the U.S. Constitution would bar the federal government from forcing states to ban marijuana.
as Jonathan Caulkins and three other drug policy scholars note in Marijuana Legalization: What Everyone Needs to Know, that "the Constitution does not allow the federal government either to order state governments to create any particular criminal law or to require state and local police to enforce federal criminal laws." Hence a treaty that purported to require such legal subjugation would not be "under the authority of the United States," and any act of Congress aimed at dictating state drug laws would not be "made in pursuance" of the Constitution.
Furthermore, the Single Convention on Narcotic Drugs says a signatory's obligation to enact criminal penalties for the nonmedical production, possession, and distribution of marijuana is "subject to its constitutional limitations." Patrick Gallahue of the Open Society Global Drug Policy Program says:
The penal provisions of the '61 convention includes the caveat: "subject to the constitutional limitations of a Party, its legal system and domestic law." How does that interact with the 10th Amendment to the U.S. Constitution, which states, "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"?...
There is an argument that [America's] unique situation regarding states' rights allows one of these states to do this [i.e., legalize marijuana without violating the treaty]. there is always the option for the United States to withdraw from the '61 convention and re-enter with reservations," as Bolivia recently did so it could legalize the traditional use of coca. But even if that never happens, and even if The reading of the treaty is correct, the federal government simply does not have the authority to do what it wants.
