Griffith died of a heart attack Sept. 28, said his cousin Ron Fellows.
Griffith was known for his work on low-budget horror-comedy films in the 1960s and 1970s and often collaborated with director Roger Corman.
Griffith wrote the script for the 1960 cult classic The Little Shop of Horrors, directed by Corman, and later helped write the screenplay for the 1986 film adaptation of the musical.
The original film, shot in black and white in about two days, featured a young Jack Nicholson in one of his early roles as a pain-loving dental patient.
Griffith, born Sept. 23, 1930, in Chicago, was introduced to Corman in 1954 through a friend. He got his first feature writing credit on Corman's It Conquered the World in 1956, and the two worked on more than a dozen films.
Griffith also wrote The Wild Angels, a Corman film starring Peter Fonda that was widely considered a forerunner to Easy Rider. He also directed a handful of films, including Eat My Dust, a movie whose script he wrote that starred Ron Howard.
Survivors include his wife, daughter and four grandchildren.