A hundred years ago a group of foreign diplomats gathered in Shanghai for the first-ever international effort to ban trade in a narcotic drug. On February 26th 1909 they agreed to set up the International Opium Commission-just a few decades after Britain had fought a war with China to assert its right to peddle the stuff. Many other bans of mood-altering drugs have followed. In 1998 the UN General Assembly committed member countries to achieving a "drug-free world" and to "eliminating or significantly reducing" the production of opium, cocaine and cannabis by 2008.
That is the kind of promise politicians love to make. It assuages the sense of moral panic that has been the handmaiden of prohibition for a century. It is intended to reassure the parents of teenagers across the world. Yet it is a hugely irresponsible promise, because it cannot be fulfilled.