Paranoid was the first single release for Black Sabbath six months after their debut album was released.
Black Sabbath bassist Geezer Butler says in Guitar World 2004
“A lot of the Paranoid album was written around the time of our first album, Black Sabbath. We recorded the whole thing in about 2 or 3 days, live in the studio. The song Paranoid was written as an afterthought. We basically needed a 3 minute filler for the album, and Tony came up with the riff. I quickly did the lyrics, and Ozzy was reading them as he was singing.”
Originally the band had wanted to call the album War Pig but the record company persuaded them to use Paranoid as the title because they deemed it less offensive.