The band "Mystic", who appear near the beginning of the film, have been revealed to be the late '60s psychedelic group Tangerine Peel, but the cross-dressing frontman is not a real member of the group. He is the film's co-writer Alan Watson.
Female lead Vanessa Shaw's real name was Phoebe Shaw. Producer Richard Gordon changed Shaw's first name from Phoebe to Vanessa because he thought Phoebe sounded too old-fashioned.
Robin Askwith improvised the moment when he stops to eat a piece of pie during the fiery climax of the picture.
The exterior of the clinic was shot at the home of Edward George Bulwer-Lytton, author of 'The Last Days of Pompeii'.