In recent years, researchers have sought to rescue hallucinogens from exile by examining their efficacy in treating certain disorders of the mind. Psychoactive substances, often derived from mushrooms, have been part of human cultures ... for thousands of years. In the 1950s and '60s, researchers assiduously explored LSD as a tool for treating mental illness and various addictions. The Central Intelligence Agency tested the drug's possibilities as a truth serum or perhaps a vehicle for mind control. Prohibitions against LSD and brethren hallucinogens, like psilocybin and mescaline, were codified in the Controlled Substances Act of 1970. Soon enough, serious scientific exploration of psychedelics dried up. In recent years, though, mind-bending drugs have begun tiptoeing back into the research mainstream. Modern scientists are ... studying hallucinogens' potential to help smokers kick the habit, to undo addictions to drugs and alcohol, to cope with cluster headaches and depression, and to deal with obsessive-compulsive and post-traumatic stress disorders. Institutions where such work is underway include New York University; Johns Hopkins University; the University of California, Los Angeles; Psychiatric University Hospital in Zurich; and Imperial College in London. Hallucinogens, while not addictive, remain officially taboo everywhere. Nonetheless ... if carefully administered, [some researchers] say, hallucinogens can reorient patients' perceptions of their place in the universe and pull them out of ruts of negative thinking.