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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 in 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-manifestation”）because they seemed to radically alter one’s state of consciousness.
重点词汇：
substance 物质；实质；财产（n.）
addict 使成瘾；成瘾者（vt./n.）
psychologist 心理学家（n.）
cocaine 可卡因（n.）
pervasive 普遍的（adj.）
sociable 社交的（adj.）
negative 否定的；消极的（adj.）
poisoning 中毒；毒害（n.）
distortion 扭曲；曲解（n.）
tolerance 宽容；忍受（n.）
symptom 症状（n.）
psychoactive 药物等对心理起作用的（adj.）
depressant 抑制剂；镇静剂（n.）
hallucinogen 致幻剂（n.）(https://www.daowen.com)
psychedelic 迷幻剂（n.）
难句解析：
①The 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.
【结构分析】句子的主干是句子的前半部分The phrase“substance abuse”is often used...to make clear...，to make clear that...是动词不定式做状语，表示目的。that后面接的是宾语从句，做动词make clear的宾语。
【重要考点】注意“make+sth.+adj.”结构，make clear that...，因为sth.是一个that引导的从句，所以放在了形容词clear的后面。另外注意as...as的用法。
②We live in 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.
【结构分析】句子的主干是We live in a society...，后面的which引导定语从句in which the medicinal and social use of substances（drugs）is pervasive，修饰society。冒号后面的部分是表示并列关系的名词词组，用于举例说明前面提出的观点，开始可以忽略不看。
【重要考点】注意冒号后面列举的前三个名词词组中的动词不定式都相当于定语成分，修饰前面的中心名词，表示其功效。
③Dependence 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.
【结构分析】句子的主干结构是Dependence is marked first by...，and then by...，中间逗号隔开的成分是“with+n.+过去分词”结构：with more and more of the substance required to produce the desired effect，做状语，用于进一步解释药物依赖的第一种表现。when the substance is discontinued是表示时间的状语从句。
【重要考点】注意and连接的两个by介词词组是并列关系，这样就能抓住句子的主干了。另外注意名词在这里的特殊意义：dependence指“对药物的依赖”，withdrawal的意思是“停止用药”。
④Psychoactive substances are commonly grouped according to whether they are stimulants，depressants，or hallucinogens.
【结构分析】句子的主干部分是Psychoactive substances are...grouped according to...，使用了被动语态。其中whether引导宾语从句whether they are stimulants，depressants，or hallucinogens，做介词according to的宾语。
【重要考点】group在句中用作动词，是“分类”的意思。
全文翻译：
从专业角度来说，除食品外，任何能改变我们生理和心理机能的物质都是药物。很多人错误地认为“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是药物。这也是现在许多内科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、烟草这样的物质如同滥用海洛因和可卡因一样有害。
我们生活在一个物质（药物）在医疗和社交方面的使用都很广泛的社会里：用来缓解头痛的阿司匹林、用来应酬的酒、早晨用来提神的咖啡，还有定神用的香烟。使用这些物质得到了社会认可，且显然具有积极的作用，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面影响，如中毒或严重的感知错乱。反复使用一种物质可以导致成瘾或对该物质的依赖。依赖的最初表现是不断增长的耐药量，要产生预期的效果需要的药剂量越来越大，而一旦中断使用就会出现难受的停药症状。
影响中枢神经系统、改变感知、情绪和行为的药物（物质）属于对神经起显著作用的物质，它们通常分为兴奋剂、镇静剂和致幻剂。兴奋剂主要起到加速或激活中枢神经系统的作用，而镇静剂则相反：减缓它的活动。致幻剂主要影响人的感知，通过多种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一词源于希腊语，意为“心灵显现”），因为它们似乎能彻底改变人的意识状态。