[@Ultimate Spidey]

Not especially. Although wolf's bane is a fairly universal poison with any species, werewolves have no special weakness to it. Due to their rapid healing abilities, they can only be weakened by copious amounts of the plant - which would likely require ingestion, which then brings up the issue of the wolf smelling the plant, or injection, which wouldn't be a simple feat with a werewolf. It'd likely have to be forced ingestion and/or injection. I would also make the plant rather uncommon, as there are already several weaknesses provided for the werewolf, so making the plant readily available would likely have led to them being far more rare.