The 73-year-old musician, most famous for his pioneering work with the Beach Boys, spent much of his younger life as a recluse after developing schizophrenia in the 1960s. The condition means he hears voices, but it only began after he started taking LSD, also known as acid.
"LSD made me more creative," he admitted to Esquire magazine. "It helped me write (Beach Boys' iconic 1966 album) Pet Sounds. But the voices started after LSD, too."
These voices still haunt Brian, but not all the time. However he admits he often struggles with the things they say to him.
"They say different things," he added. "Like 'we're going to hurt you'. It's crazy! But not all the time, yeah. Like every other day."
Brian was treated for drug addiction and mental health issues by Dr Eugene Landy in the 1970s and '80s in a desperate bid to put a stop to his reclusive existence.
Dr Landy eventually helped Brian to start functioning again, but he later lost his professional licence and was banned from treating the musician following accusations he had brainwashed the star with his extreme method of therapy which involved round-the-clock supervision and total isolation from family and friends.
Now Brian counts routine as an important part of his life, and added to the publication: "I have my breakfast. I comb my hair. And I go to the park and I take walks. And then I come home and watch television. Like the news or Jeopardy and Wheel of Fortune."
He also plays the piano to stay content, revealing the secret to his happiness is "that I don't use drugs and I play the piano."
The tale of Landy's therapy sessions with Brian were told in last year's movie (15) Love & Mercy, with Paul Giamatti playing the psychologist. Brian previously said that he was blown away by the actor's realistic portrayal of Landy.