Therianthropy is a transformative magia morbus, or magical disease.
A weredragon is a pendragon that is afflicted with lycanthropy. When normal, they are just like any other pendragon. Often times, they don't even know the other side exists until it manifests itself. When this happens, the pendragon will seem to revert to basic instincts, and will usually communicate in a series of growls and grunts. Warning signs of this can be detected in the eyes, which usually change colour when the 'dragon in question is transformed.
When a weredragon transforms into the feral state, they lose abilities such as logic, communication, and just plain thinking about their actions. However, this is compensated for by an increase in stamina, strength, and often times, more powerful spells in the state. A weredragon is extremely dangerous when transformed, do not attempt to subdue the said dragon. Doing so will only cause it to struggle harder, reverting into the feral state even deeper.
Transformations can happen for a number of reasons. Most 'dragons only transform at certain times, such as when the moon is full.
However, a few will only be triggered by severe emotional distress, such as watching ones love die. These are the worst type to encounter. Often times, these are the ones who have their alter-egos created by a traumatizing event, releasing hate, rage, and sorrow in a massive burst.
Sometimes, a normal pendragon is born with the alter-ego, sometimes getting it through a curse, and sometimes developing it after a very traumatic event.