Drew was in Culver City Thursday and he railed on the trolls who have been attacking Pete, calling them "evil." He says Pete is in a super delicate state after a gut-wrenching breakup with Ariana, and people need to get off his back ... because, at this point, his life depends on it.

As we reported, Ariana rushed to see Pete at 30 Rock Saturday after he posted apparent suicide threats ... something that was triggered by one of Ariana's posts in which she went after Kanye West, saying "stop weaponizing mental health. everyone." Pete, who suffers from mental health issues, took it in a deeply personal way.

Bottom line ... Dr. Drew says Pete needs some space to heal.