英语语法分析

Caffeine, the stimulant in coffee, has been called "the most widely used psychoactive substance on Earth".

咖啡中的咖啡因因被称为“地球上使用最广泛的精神活性物质”。

The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs.

问题在于，这种化合物对大脑有混合作用，这种情况在服用精神药物时并不少见。

It is psychoactive, a stimulant and addictive.

它作用于人的神经系统，是一种兴奋剂，让人上瘾。