The United Nations says the price of Afghan opium rose dramatically in 2011.
The UN Office on Drugs and Crime Opium says poppy farmers in Afghanistan probably earned more than $US1.4 billion last year - an estimate equivalent to 9% of the country's GDP.
Prices started to rise in 2010 after the poppy crop was hit by a fungal disease.
Agency head Yury Fedotov said opium helped fund the Taliban and fuelled corruption in Afghanistan.
Around 90% of the world's opium comes from Afghanistan, according to the agency, which carries out an annual survey of production there.
The Afghan Opium Survey for 2011 found that the value of opium in the country had increased by 133%.
The BBC reports last year's survey had predicted a rise in poppy planting as farmers responded to higher market prices.