Study finds oil makes up half of Afghanistan 's gross domestic product . Agency encourages NATO forces to attack the problem aggressively . Drugs funds insurgency ; heroin grows unchecked in Taliban camps . U.N. drug policy advocates providing income alternative for poppy farmers .
Study finds opium makes up half of Afghanistan 's gross domestic product . Agency pushes NATO forces to attack skyrocketing problem aggressively . Drugs funds insurgency ; poppy trade unchecked in Taliban strongholds . U.N. drug chief advocates providing income alternative for poppy farmers .