Lycanthropy (synonyms: werewolfism; name examples: The Moon Plague) is a disease or condition in which a person transforms into a werewolf or human-wolf hybrid. This transformation may occur only during the full moon and be impossible to stop, or may be performed at will depending on the fictional setting. Once a person has transformed, they may retain their intelligence and personality, or they may become a savage and hungry beast. Lycanthropy is often spread via a bite from an infected person while they are transformed. Often, a person suffering from lycanthropy can only be killed using a silver weapon or bullet.

When incorporating lycanthropy in a fictional world, consider if those suffering from the disease are ostracized from society (or kept separate from it). Werewolves in fictional worlds often form their own communities, with their own taboos, customs, and traditions. Often worldbuilders will incorporate the social hierarchies of wolfpacks as the basis for these societies. These communities may be at war with other magical creatures, such as vampires. If a person is no longer in control of themselves while transformed, they may try to imprison themselves during a full moon or otherwise render themselves safe to others. Consider if there is a cure for lycanthropy in your own fictional world.

If a full moon causes a transformation, do other types of moons have an impact?