when后面所跟的动词的主语与主句主语一致.
when done:表示动作完成后发生主句描绘的情形,与主句主语是被动的关系
When asked by the police,he said that he remembered nothing .
when being done:与主句同时发生,主句主语与该动作是被动关系；
例如 when being laughed at,the boy smiled and walked away.
when doing:与主句同时发生,主动.
例如 when doing the exam,we should be careful
when to do 不适用于这种情况
when to do 中的不定式表示“什么时候要去做什么事”
例如 I don't know when to hand in my homework,
因此,在该句子中 “吃药”
drug 和 take 是被动关系,用taken