Director Hy Averback said in an interview that one day Peter Sellers refused to shoot a scene until a crew member standing off camera changed clothes. The superstitious Sellers claimed the outfit was the "wrong color". Shooting had to stop while they went to wardrobe and got a different color outfit for the crew member.
The film's title is a tribute to Gertrude Stein's lifelong partner, Alice B. Toklas, who published a cookbook in 1954 that contained the first printed recipe for hash fudge. In one of the movie's most famous scenes Harold Fine unknowingly serves marijuana-laced brownies baked by Nancy to his parents and fiancée.
A week into the shoot, Peter Sellers invited Paul Mazursky to his home for a meeting. Given their previous differences, this was a shock in and of itself. At the meeting, Sellers apologized for the misunderstanding and begged Mazursky to take over the direction. Mazursky refused to do it.
Warner Brothers/Seven Arts sold the film with the tagline "The saga of Harold...from dedicated lawyer to dedicated dropout." Afraid of the film's humorous depiction of recreational drug use, the studio backed off from Paul Mazursky's suggestion that they make the poster more psychedelic.
This was not a happy period in Peter Sellers's life. He was miserable working in the U.S. and furious that his second wife, Britt Ekland, had signed to make "The Night They Raided Minsky's (1968)," which was filming on the East Coast while he was working in Hollywood. As a result, he acted out on the set a great deal. At one point, he was convinced the crew hated him and was leaking unfavourable stories about him to the press, so he tried to have them all fired.