The war in northern Yemen, between tribal rebels and the governments of Yemen and Saudi Arabia, is having one positive effect; it is reducing the supply of illegal drugs. For decades, the desolate 1,700 kilometer border between Yemen and Saudi Arabia has been largely unguarded, and increasingly popular with smugglers bringing forbidden goods (like drugs and alcohol) to feed the growing affluence of oil rich (but socially conservative) Saudi Arabia. Now, Saudi warplanes patrol the border, shooting (on sight) any vehicles crossing illegally (not at the guarded crossing points).
As a result, smuggling activity has decreased over fifty percent. While hard drugs and booze can be brought in via other routes (Iraq being a favorite), the narcotic leaf Khat, cannot. Khat is grown in Yemen, and delivered quickly to Saudi customers each day. Khat must be relatively fresh, or else it loses its effect. So other forms of smuggling will not be very effective, because they take too much time. Khat gives you more of a buzz than caffeine or nicotine, but less than stronger drugs. The shortage has seen the price of Khat more than triple in the last month.