Lycanthropy

Lycanthropy was a condition, disease or curse that caused humanoids and giants to change form, usually into hybrid humanoid-animal states.

Transfiguration
Those who were afflicted with lycanthropy often didn't have full control over their ability to transform and could be triggered into doing so by a certain circumstance(s). The most common of these in the Realms and elsewhere was a moon, such as Toril's Selûne, entering its full moon phase. By contrast, true lycanthropes were said to be generally unaffected by such triggers.

Notably, exposure to the Selûnite substance moonfire could give a lycanthrope complete control over their transformations for a span of seven moons. And if a silverstar (a variety of Selunite specialty priest) was infected by a lycanthrope who was morally upstanding, without any care for ethical standing, or the moral and ethical outlook of that creature was in line with that of the silverstar, then the priest or priestess became a natural lycanthrope, rather than an afflicted one.

The process of transfiguring between lycanthropic states was a painful experience for all but true lycanthropes.

Mental Effects
Once the transformation was complete, an afflicted lycanthrope's personality would be subsumed and overtaken by a ravenous, predatory mindset until they returned to their original form. This altered state of personality slightly varied between strains of lycanthropy, incorporating behavioral aspects of their strain's animal. This personality typically retained all the memories possessed by their humanoid state.

When an afflicted werewolf finally did return to their base humanoid form, their memories of the time spent in their animal or hybrid forms was either hazy or outright forgotten, as were any memories of the pain they experienced during the process of transfiguring between states and of the transformation process itself. If an afflicted did manage to retain memories of the time spent in their animal or hybrid form they would be indistinct and surreal, as if one were recalling a nightmare.

By contrast, true lycanthropes and silverstars retained their personality in their animal or hybrid forms and their memories of the time spent in either form remained intact in their humanoid forms.

Vulnerabilities
Lycanthropy brought with it a tremendous resilience to most forms of damage, that was generally seen and known to be surpassable only by magic and silvered weaponry. However, some monster hunters such as Van Richten and the Silver Stake organization found that all lycanthropes suffered from at least one or more non-magical vulnerabilities that varied between each type, and in some cases between individuals. This vulnerability was a severe allergy to a specific type of plant and mineral, which they would be sensitive to in their humanoid, hybrid, and animal form. Low doses could incapacitate or weaken them, while greater doses could prove deadly.

Notably, through a boon with their goddess Selûne, lycanthrope silverstars lacked the famed vulnerability to silver.

Notable Lycanthropes

 * The Gray Wolf tribe of Uthgardt barbarians.

Trivia

 * No one deity in the Realms truly had the condition of lycanthropy as a part of their divine portfolio, though priesthoods had conflicting claims on this topic as there were some gods often associated with the condition. For instance, some priests of Nobanion claimed that he had dominion over the condition, but not lycanthropes themselves.
 * Lycanthropy was entirely absent on the Malatran Plateau.
 * Priests of the Church of Moander, noted for their general resilience towards all manner of diseases, were said to be immune to contracting lycanthropy.