難句解析：
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.
▲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...是動詞不定式作狀語，表示目的。that后面接的是賓語從句作動詞make clear的賓語。
△注意make+sht.+adj.：make sth. clear，這里因為sth.是一個that引導的從句，所以放在了形容詞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.
▲句子的主干就是We live in a society...，后面which引導定語從句in which the medicinal and social use of substances(drugs) is pervasive，修飾society。冒號后面的部分是并列關系的名詞詞組，用來舉例說明前面提出的觀點，開始可以略去不看。
△注意冒號后面列舉的前三個名詞詞組中的動詞不定式都相當于定語成分，修飾前面的中心名詞，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.
▲句子的主干結構是Dependence is marked first by..., and then by...，其逗號隔開的成分是with+n.+過去分詞：with more and more of the substance required to produce the desired effect作狀語，用來進一步解釋藥物依賴的第一種表現。when the substance is discontinued是表示時間的狀語從句。
△注意and連接兩個by開始的介詞詞組是并列關系，這樣就能抓住句子的主干了。另外注意名詞在這里的特殊意義：dependence指“對藥物的依賴”，withdrawal的意思是“停止用藥”。
④Psychoactive substances are commonly grouped according to whether they are stimulants, depressants, or hallucinogens.
▲這是一個簡單句。句子的主干部分是Psychoactive substances are... grouped according to...，使用了被動語態。其中whether引導賓語從句whether they are stimulants, depressants, or hallucinogens作介詞according to的賓語。
△group這里用作動詞，是“分類”的意思。
來源:可可英語 http://www.ccdyzl.cn/kaoyan/201407/310047.shtml