我们居住在一个物质的药用和社会使用泛滥的社会里：一片阿司匹林用来减轻头痛，一些葡萄酒用于交际，咖啡在早晨可以提神，何时这些社交上被接受而显然也是有益的物质使用变成滥用了呢?大多数物质过多摄入后会产生诸如中毒等的负面影响。对于某种物质的重复使用同样能导致上瘾

According to a recent report by the UNEP, if car numbers keep increasing at the present rate, there will be more than a billion on the road by 2025. Today, motor vehicles put out 900 million tones of carbon dioxide a year--about 15 percent of our total output. More vehicles will mean more global warming. Also by 2025, two-thirds of the world’s people will live in cities, so traffic jams and pollution will loom large in most people’s lives.

We live in a society in which the medicinal and social use of substances is pervasive: an aspirin to quiet a headache, some wine to be sociable, coffee to refresh oneself in the morning. When do these socially acceptable and apparently constructive uses of a substance become misuses? Most substances taken in excessively will produce negative effects such as poisoning. Repeated use of a substance can also lead to addiction or substance dependence. Dependence is marked first by an increased tolerance, and then by the appearance of withdrawal symptoms when the substance is discontinued.