A home-grown marijuana plant is grown inside an apartment in Washington, D.C. (Photo by Astrid Riecken For The Washington Post)

The global war on drugs has proven "disastrous" and "humankind cannot afford a 21st century drug policy as ineffective and counter-productive as the last century’s." So say more than 1,000 world leaders, including 27 members of the House of Representatives and six U.S. senators, in a letter to the United Nations ahead of a major international drug summit happening this week.

The letters signatories also include 24 current and former law enforcement officials, 37 members of the clergy, more than 230 health and medical professionals, and a colorful slate of celebrities, athletes and business leaders, including DJ Khaled, Michael Douglas, Tom Brady and Warren Buffett. The two Democratic presidential candidates, Hillary Clinton and Bernie Sanders, have also signed on to the letter.

"The drug control regime that emerged during the last century has proven disastrous for global health, security and human rights," the letter states. "Focused overwhelmingly on criminalization and punishment, it created a vast illicit market that has enriched criminal organizations, corrupted governments, triggered explosive violence, distorted economic markets and undermined basic moral values."

The U.N. General Assembly will hold a special session on global drug policy in New York this week. The purpose of the meeting is to set the tone and focus of global drug policy for the coming decades.

The last time the U.N. held such a session was in 1998. Proceeding under the official motto of "a drug-free world -- we can do it," member states vowed to "promote a society free of drug abuse" and to "develop strategies with a view to eliminating or significantly reducing" the production and use of illicit substances by 2008.

Since then, of course, a number of U.S. states have voted to fully legalize marijuana for recreational use. Portugal decriminalized the use of all illicit drugs. And the United States has seen an explosion in the abuse of prescription painkillers and heroin, and deaths caused by overdoses of those two drugs.

Reformers had hoped this week's special session would represent a change of course for the international drug control regime. But if the draft declaration that will be discussed at the meeting is any indication, this is unlikely. The language about promoting a society "free of drug abuse" and the need to "eliminate" the production of drugs remains in place.

VICE News reported that several diplomats pointed to Russia, China, Iran and Saudi Arabia as the primary opponents to changing the language.

"Basically, the bad guys had the upper hand" in negotiating the language of these documents, according to Ethan Nadelmann of the Drug Policy Alliance, a reform group. "They were able to make sure that nothing bold or stunning happened in these things."

The irony of the U.N.'s inaction on drugs is that it makes it more likely member states will continue to chart their own paths forward on drug policy. State-level marijuana legalization in the United States has enraged the Russian director of the U.N.'s anti-drug program, but U.S. officials simply assert that the treaties allow for considerable "flexibility" in addressing drug issues.

While this is a difficult diplomatic needle to thread, there's little to stop officials in the U.S. -- and elsewhere -- from issuing appeals to this flexibility whenever they want to alter drug policy approaches in their own countries.

Indeed, the lesson of drug policy over the past 18 or so years seems to be that like politics, all drug reform is local. In the United States, for instance, individual states have pioneered new directions on drug policy, particularly marijuana policy, in the face of gridlock at the federal level.

The U.N., meanwhile, has proven itself to be an even less-nimble organization than the federal government -- so don't expect it to be a significant player in drug policy discussions going forward.

This story has been updated.