Theaters playing this film gave free "barf bags" to the viewers.
The US distributors of this film, Hallmark Releasing, advertised it as "guaranteed to make you sick" and backed it up with thousands of vomit bags advertising the film.
The original ending was supernatural with the dead rising and pulling Christian into the abyss, but the second director hated it and had the negatives destroyed. The only remaining footage are stills that can be seen on the DVD release.
After it was already censored for its theatrical release, the film was banned in Germany from its video release in the 1980s until 2016. Only then, the banishment was lifted (after The Texas Chain Saw Massacre (1974), this is only the second time this has been achieved).
Originally Michael Reeves was set to direct this film, but he died shortly before production was to begin. The producers then decided to hire Michael Armstrong, who worked as Reeves' assistant on Witchfinder General (1968).