This was prolific director John Gilling's last film. He hadn't planned to make it, but he was on vacation in Spain when his friend, actor/director Paul Naschy, asked him to direct it for him.
Often called the unofficial fifth film in the "Blind Dead" franchise created by Armando de Ossorio.
What Alfred Dawson smokes is kief, not hashish. Hashish comes in wax form, kief comes in powder form, and what Alfred Dawson puts into his pipe throughout the film is a powder.