If you listen to the ancillary tracks on the superb 2011 reissue The Smile Sessions by the Beach Boys, you'll hear Brian Wilson experimenting with drugs while in complete control of his music. He asks others in the studio if there are any more "hash joints" left and idly comments that the LSD is starting to kick in, but at the same time rules the studio musicians present with an iron fist; for example, he instructs a guitarist exactly which strings on the guitar he wants him to strum.
But holding such a firm grasp on his mind was another matter. Shattered by a lack of support from his fellow band mates in his new musical direction and driven mad trying to compete with the Beatles (Sgt. Pepper's Lonely Hearts Club Band was partly a response to the Beach Boys' Pet Sounds, which had been a response to the Beatles' Rubber Soul), Wilson shelved Smile, which would have been his masterpiece.
Subsequent years were not kind to Wilson. He got seriously addicted to cocaine, his weight ballooned and he descended into mental illness and was put under the care of a manipulative psychologist named Eugene Landy. In the early '80s, he was fired from the Beach Boys; a once unthinkable move for a band built around his songwriting talents. He's made many comebacks since, even rejoining the Beach Boys. Still, one can't help but wonder what might have been if he'd recorded all the songs he's written over the years that were only heard by those in proximity to the piano in a sandbox in his living room. For his part, however, Wilson doesn't altogether condemn drug use; speaking to a Canadian radio station in 2011, he credited marijuana with helping him write Pet Sounds and LSD with an assist on "California Girls."