Ancient Iraq is the source of some of the earliest written accounts of opium poppy production. As far as 5,000 years back, the plant known to the ancient Sumerians as Hul Gil, the "joy plant," was cultivated in the fertile plains of Mesopotamia. Now, according to the London newspaper The Independent, opium production is once again underway in Iraq.

While concern has been rising since the US invasion in 2003 about Iraq's role as a conduit in the international drug trade, particularly the distribution of Afghan heroin smuggled through Iran, into Iraq, and thence to wealthy Middle Eastern and Western European markets, the apparent turn toward poppy cultivation in Diwaniya is a first.
The reported poppy planting comes amidst increasing, if largely unreported, conflict in southern Iraq between the Mehdi Army of firebrand cleric Muqtada al-Sadr and the Badr Organization, the armed wing of Supreme Islamic Iraqi Council. At least one source told The Independent that the current fighting in the south started over control of opium production, but has since spread into a general turf war.

(graph from WOLA/AIN memo, link below)
This graph shows what about $10 billion in US taxpayer dollars has accomplished. Note that while coca production has shifted within the region, the 1992 levels and the 2005 levels are essentially identical.
Why is our coca eradication policy not subjected to cost-benefit analysis? Is there anyone who will argue that it is working? If so, I'd like to hear it.
To be fair, that $10 billion has accomplished some things. It has engendered massive social conflict in all three countries, it has led to tens of thousands of peasant farmers being arrested as drug traffickers, it has led to thousands of deaths (especially in Colombia, where the eradication policy is part of the US's broader military intervention in that country's festering civil war). Your tax dollars at work.
$10 billion is a lot of money. Heck, we could finance the Iraq war for a few weeks with it! Or we could give $100,000 college scholarships to 10,000 students. Or build $100,000 homes for 10,000 families. Or numerous other programs that, unlike the coca eradication program, might actually accomplish something.
By the way, I came across the graph above in a 