Well the farmers in Afganistan couldn't make money with normal crops so they raised Poppies.

Farmers in Colombia could make money with Normal crops so they raised Coca Leaf.

Maybe the Midwest farmers who can't make money raising corn could raise Hemp?

But if they did,  How would the CIA increase it's slush fund income like they do controlling the other two examples??

They could corner the US 'Munchies' markets..