[长难句突破]

We live a society in which the medicinal and social use of substances (drugs) is pervasive: an aspirin to quiet a headache, some wine to be sociable, coffee to get going in the morning, a cigarette for the nerves.

主体句式：We live a society in which...

结构分析：本句的主干中包含了一个in which引导的定语从句，从来修饰society。冒号后面的几个并列结构以逗号隔开，用来补充说明前文的"substances (drugs) is pervasive"的具体情况

Dependence is marked first by an increased tolerance, with more and more of the substance required to produce the desired effect, and then by the appearance of unpleasant withdrawal symptoms when the substance is discontinued.

主体句式：Dependence is marked first by... and then by ...

结构分析：本句的主干为"Dependence is marked"，后面由以by引导的两个并列介词结构构成，由and连接。第一部分中包含了一个with 引导的介词状语，把主句的内容进一步展开说明。第二部分的最后是一个when引导的时间状语从句，用来修饰"the appearance of unpleasant withdrawal symptoms"。

[全文译文]

Technically, any substance other than food that alters our bodily or mental functioning is a drug. Many people mistakenly believe the term drug refers only to some sort of medicine or an illegal chemical taken by drug addicts. They don't realize that familiar substances such as alcohol and tobacco are also drugs. This is why the more neutral term substance is now used by many physicians and psychologists. The phrase "substance abuse" is often used instead of "drug abuse" to make clear that substances such as alcohol and tobacco can be just as harmfully misused as heroin and cocaine.

We live a society in which the medicinal and social use of substances (drugs) is pervasive: an aspirin to quiet a headache, some wine to be sociable, coffee to get going in the morning, a cigarette for the nerves. When do these socially acceptable and apparently constructive uses of a substance become misuses? First of all, most substances taken in excess will produce negative effects such as poisoning or intense perceptual distortions. Repeated use of a substance can also lead to physical addiction or substance dependence. Dependence is marked first by an increased tolerance, with more and more of the substance required to produce the desired effect, and then by the appearance of unpleasant withdrawal symptoms when the substance is discontinued.

Drugs (substances) that affect the central nervous system and alter perception, mood, and behavior are known as psychoactive substances. Psychoactive substances are commonly grouped according to whether they are stimulants, depressants, or hallucinogens. Stimulants initially speed up or activate the central nervous system, whereas depressants slow it down. Hallucinogens have their primary effect on perception, distorting and altering it in a variety of ways including producing hallucinations. These are the substances often called psychedelic (from the Greek word meaning "mind-manifesting") because they seemed to radically alter one's state of consciousness.

从技术角度说，除了食品外，任何能改变我们生理和心理机能的物质都是药物。很多人误认为"药物"这个词仅仅指某些药品或是吸毒者服用的违禁化学品。他们没有意识到诸如酒精、烟草这些我们熟悉的物质也都是药物。这也就是为什么现在许多医生和心理学家使用"物质"这个更加中性的词的原因。他们常用"物质滥用"而不用"药物滥用"来清楚表明滥用酒精、烟草这样的物质与滥用海洛因和可卡因一样有害。

在我们生活的这个社会中，物质（药物）在医疗和社交方面的使用都很广泛：服用阿斯匹林可以缓解头痛，应酬时要喝酒，早晨醒来喝咖啡来提神，抽一支香烟可以稳定情绪等等。使用这些物质得到了社会的认可，而且很明显具有其积极的作用，但什么时候就变成滥用了呢？首先，大多数物质的过量使用都会产生负作用，如中毒或严重的感知错乱。反复使用一种物质可以导致上瘾、也就是对这种物质的依赖。依赖的最初表现是不断增长的耐药量，用量越来越大才能达到预期效果，而一旦中断使用就会出现非常不舒服的停药症状。

作用于中枢神经系统、能改变感知觉和行为的药物（物质）被称为对神经起作用的物质，这一类物质通常分为兴奋剂、镇静剂和幻觉剂。兴奋剂主要起到加速或激活中枢神经系统活动的作用，而镇静剂则相反：使其活动变缓。幻觉剂主要影响人的感知，通过各种不同的方式对感知加以扭曲或改变，其中包括产生幻觉。这些物质常被认为能"引起幻觉"（psychedelic一词源自希腊语，其意思是"心灵显现"），因为它们似乎能改变人的意识状态。