Unfortunately, he took some medicine which was har

有些答案中提示去掉which was ，那样medicine和harmful之间是主动还是被动的关系。

Unfortunately, he took some medicine which was harmful to his lungs/heart.

【翻译】不幸的是，他服用了一些对他的肺部/心脏有害的药物。

从网友的提问看，好像是不要which was，变成形容词短语作定语。

其实，保留which was 是定语从句，同样正确。

was harmful to 没有“主动被动”问题。这是一个系表结构，不是及物动词。