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.

Vulnerabilities
Lycanthropy brought with it a tremendous resilience to most forms of damage, that was generally seen and known to be surpasable 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 nonmagical 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.

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.