Opium

Opium poppies have traditionally been grown in Afghanistan, and, with the war shattering other sectors of the economy, it became the number one export of the country.
The Taliban have provided an Islamic sanction for farmers ... to grow even more opium, even though the Koran forbids Muslims from producing or imbibing intoxicants. Abdul Rashid, the head of the Taliban's anti-drugs control force in Kandahar, spelled out the nature of his unique job. He is authorized to impose a strict ban on the growing of hashish, `because it is consumed by Afghans and Muslims.` But, Rashid told me without a hint of sarcasm, `Opium is permissible because it is consumed by kafirs in the West and not by Muslims or Afghans.`
But in 2000 the Taliban banned opium production, a first in Afghan history. In 2000, Afghanistan's opium production still accounted for 75% of the world's supply. On July 27, 2000, the Taliban again issued a decree banning opium poppy cultivation. According to opioids.com, by February 2001, production had been reduced from 12,600 acres (51 km²) to only 17 acres. When the Taliban entered north Waziristan in 2003 they immediately banned poppy cultivation and punished those who sold it.Another source claims opium production was cut back by the Taliban not to prevent its use but to shore up its price, and thus increase the income of poppy farmers and revenue of Afghan tax collectors.
However, with the 2001 US/Northern Alliance expulsion of the Taliban, opium cultivation has increased in the southern provinces liberated from the Taliban control, and by 2005 production was 87% of the world's opium supply, rising to 90% in 2006.