A Scanner Darkly (2006)

In a dystopian future, an undercover cop becomes addicted to a dangerous drug and struggles to maintain his identity. As he infiltrates the drug scene, he develops romantic feelings for a woman who refuses his advances, leading to paranoia and confusion. Eventually, he discovers that he himself is the target of surveillance and his true identity is revealed. He goes through withdrawal and is sent to a rehabilitation center, where he uncovers the truth about a corporation behind the drug. Despite his damaged state, he plans to expose them.