In Afghanistan, opium production is growing like a weed — and nothing, not even billions of dollars of U.S. money, has been able to quell it.

According to the United Nations, the war-torn nation provides 90 percent of the world's supply of opium poppy, the bright, flowery crop that transforms into one of the most addictive drugs in existence.

And as the Centers for Disease Control and Prevention sounds the alarm about a worsening heroin epidemic here in the U.S., opium production in Afghanistan shows no signs of slowing down.

"Afghanistan has roughly 500,000 acres, or about 780 square miles, devoted to growing opium poppy. That's equivalent to more than 400,000 U.S. football fields — including the end zones," John Sopko, Special Inspector General for Afghanistan Reconstruction, said in a speech in May.

The U.S. has spent $8.4 billion in counternarcotics programs in Afghanistan. But opium output keeps rising: Fifteen years ago, Afghanistan accounted for just 70 percent of global illicit opium production.

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The problem, experts say, stems from the country's rampant corruption and the impoverished farmers who feel they have no choice but to contribute to the drug supply chain.

"It's much easier if you're a farmer to grow opium than to grow saffron or to grow grapes or something like that," said Jonah Blank, a senior political scientist and Afghanistan expert at the RAND Corporation in Washington, D.C. "Opium is a much more profitable crop. It requires a lot less infrastructure. You can grow opium practically anywhere, and it doesn't need to be refrigerated, it doesn't need complex transportation networks."

What seals the deal for many farmers is taxes: In Taliban-controlled areas — or even areas the Taliban doesn't technically control, but still has enough influence that they can intimidate local farmers and officials — the Taliban collects taxes.

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"They demand taxes not on what you're growing, but on what your land could produce if you were growing opium. So if you decide you don't want to grow opium, the Taliban's response is, 'Fine, pay me the equivalent amount and you can grow whatever you want,'" Blank said.

Nasir Shansab, author of "Silent Trees: Power and Passion in War-Torn Afghanistan," said opium production has "become part of the economy."

"It brings money and imported material and consumer goods into Afghanistan," he said. "Afghanistan is poverty-stricken and farmers have difficulty getting proper returns for their normal products. They're almost forced to do that to survive," he said.

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Neither of the U.S. antinarcotics approaches have yielded success. From 2001 to 2009, the U.S. tried an eradication strategy, giving the Afghan government resources to wipe out poppy crops. This only eliminated a tiny percentage of suppliers, and led to more local corruption: Meaning governing warlords got richer as individual farmers got poorer.

"The whole system is criminalized. It runs through the police, the courts, through the whole government system," Shansab said. "When we talk about corruption in Afghanistan, which is rampant, now this is part of it."

The current approach offers farmers the chance to substitute their opium crops with legal crops, thanks to billions of dollars in U.S.-funded agricultural development.

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But while that helped Laos and Thailand, two former heavyweights in the global opium production trade, get off the list of major suppliers in the 1990s, it appears to only be making Afghanistan's problem worse by not giving farmers all the tools they need to grow.

"The bottom line — record opium cultivation and production — clearly shows we are not winning the war on drugs in Afghanistan," Sopko, the special inspector general, said.

Opium hasn't always blossomed this freely in Afghanistan. Before being ousted by the U.S., the Taliban banned opium in 2000, arguing that growing drugs was anti-Islamic. Opium dropped dramatically in the coming year, stunning the international community — but Blank, the Afghanistan expert, has doubts about their motive.

"The theory that makes the most sense to me is that there was such a glut of opium on the market that the Taliban basically allowed its favorite suppliers to store opium for the next year to drive the prices up, expecting that they would around for many years to come, and that they could sort of be the OPEC of opium," he said.

After the Taliban was deposed, the ban was eliminated. But with so much to fix in Afghanistan, the U.S. was unable to keep crops from popping back up.

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"The biggest problem from a U.S. security perspective is not opium. It's what opium leads to," Blank said. "You can't fight counterinsurgency and counternarcotics at the same time. Essentially, you're pulling in two different directions. Which is more important? From a security standpoint, I think counterinsurgency is more important."

The answer, he said, is to bolster Afghanistan's government.

"Corruption and government efficiency are the first things that really need to be looked at. There's so much money to be made from narcotics that if corruption isn't coming from drugs, it will be coming from something else."