http://goo.gl/G7qwE3
Khat is a plant that has grown in Yemen for thousands of years. Khat leaves when chewed give you more of a buzz than caffeine or nicotine, but less than stronger drugs. It is addictive and until the 1950s was grown by farmers for their own personal use as a stimulant. Khat was used like that long before anyone figured out how to use coffee beans to produce a stimulating liquid. One thing that kept Khat local was the fact that the leaves quickly lost their potency a few days after being picked. In other words, Khat did not travel well while coffee beans and tea leaves did. That all changed after World War II when roads, trucks and air transport became widely available. Suddenly Khat had an international market for those who could afford to pay and had a taste for it.
Khat has created another problem; the importation of powerful and often forbidden insecticides, to facilitate the growing of more Khat. Since the Khat leaves are chewed, using too much, or too poisonous (to humans) insecticide makes the users sick. Many Khat growers are more concerned with producing more Khat than they are in keeping their customers healthy. The Yemeni government is struggling to keep illegal insecticides out of the country, if only to prevent Yemeni Khat users from getting sick. Just as Colombia and Afghanistan were thrown into chaos by major drug gangs (producing cocaine and heroin, respectively) Yemen is being brought low by Khat. It is all low key and generally off the mass media radar, but it is very real.