Several points about chronic use are also evident. After years of daily smoking, people do not show any changes in brain structure, unless they started using the drug before adulthood. They also rarely show deficits on standard measures of intelligence, thinking, or ability. Yet sensitive tests show changes in brain function. Chronic users can perform more poorly on complex, difficult tasks that require fast reactions and focused attention. The practical implications of these findings continue to generate debate. Studies of chronic users have yet to reveal dramatic health problems, but their lungs show changes that suggest an increased risk for cancer. Chronic users do not show a consistent, identifiable, amotivational syndrome. Yet people who are high all the time probably do not get a great deal of work done. Compared to alcohol, cigarettes, and overthe-counter medications, occasional marijuana use causes little harm.

The future for cannabis holds many possibilities. Research on the cannabinoids and their receptors will undoubtedly continue to tell more about the human mind and body. This work could reveal additional information about the brain and immune system. Further work can test the efficacy of marijuana and the cannabinoids as medical treatments. Data on the long-term health effects of the drug could address many unanswered questions, particularly those concerning the lung and brain. Techniques may evolve to limit the drug's negative consequences, like recent efforts to develop the vaporizer to reduce noxious components of smoke. Treatments for problem users could improve. In addition, laws related to the drug may change.

Cannabis became essentially illegal in the United States in 1937. Despite over 60 years of prohibition, more people have used the drug than ever before. Police arrest over half a million Americans each year for crimes related to marijuana. Government spends billions annually on marijuana control. Several authors suggest that alternative policies may prove cheaper, send fewer people to jail, and maintain respect for the law. After reviewing this literature, readers may agree. These plans include legalization, decriminalization, and licensing users. The experiences of other countries suggest little change in levels of drug problems after decriminalization, but many people feel that these experiences would not apply in the United States. Nearly a dozen states have decriminalized the drug at one time or another with little impact on use. Federal prohibition remained, however, which may have kept rates of consumption down. Yet most people who do not use the drug claim they have no interest regardless of its legal status. Changes in legislation have the potential to save money and increase respect for the law. They also might have unforeseeable long-term consequences. . .