Here comes the backlash: one day after Uruguay became the first country in the world to legalize marijuana, a United Nations drug control agency issued a press release condemning the country's decision.

The agency, the International Narcotics Control Board, is an independent and quasi-judicial body of the UN. It was established in 1968, in the wake of the 1961 Single Convention on Narcotic Drugs treaty, to serve a primarily advisory role to countries. For instance, it has been charged with identifying "the weaknesses in national and international [illicit drug] control systems and contribut[ing] to correcting such situations." So naturally, the organization remains steadfastly opposed to drug legalization, including marijuana.

From the INCB's 2002 annual report:

States have a moral and legal responsibility to protect drug abusers from further self-destruction. States should not give up and allow advocates of legalization to take control of their national drug policies. Governments should not be intimidated by a vocal minority that wants to legalize illicit drug use. Governments must respect the view of the majority of lawful citizens; and those citizens are against illicit drug use.

In response to Uruguay's decision, the INCB expressed "regret" and "surprise" that Uruguay's leaders would go against the international treaty they are a part of – and that they would not take up the organization's calls for a "dialogue" before passing the law.

The INCB explained why it still opposes efforts to legalize marijuana anywhere. According to its president, Raymond Yans, marijuana poses serious health consequences, including addiction:

The decision of the Uruguayan legislature fails to consider its negative impacts on health since scientific studies confirm that cannabis is an addictive substance with serious consequences for people's health. Cannabis… may also affect some fundamental brain functions, IQ potential, and academic and job performance and impair driving skills.

Additionally, the INCB expressed its doubt that legalization could reduce drug-related crime. The organization claims the theory is based "on rather precarious and unsubstantiated assumptions."

Uruguay's leaders have not yet commented on the INCB's criticism.

Another of the UN's drug control bodies, the United Nations Office of Drugs and Crime, which offers advisory and financial assistance to countries' prohibition efforts, also criticized Uruguay's new law. "It is unfortunate that, at a time when the world is engaged in an ongoing discussion on the world drug problem, Uruguay has acted ahead of the special session of the UN General Assembly planned for 2016," said the drug office's spokesman, David Hodge.

Under the legalization bill, which President Mujica championed, the government will grow marijuana, distribute it to licensed pharmacies, and impose a roughly $1/gram price cap. Adults will be allowed to buy up to 40 grams (about 1.4 ounces) each month. The bill also allows home cultivation of up to six plants. Uruguay's drug control agency has until mid-April to write regulations for the new system.