One Wolfsbane is used during the fight against Mayong Mistmoore in Mistmoore's Inner Sanctum to prevent wolf adds from spawning. He will say something like "get that foul plant out of my sight..." about one minute into the fight. At that point he will select a random person among those that have a Wolfsbane in their inventory and take (destroy) it. You will need one Tunarian Wolfsbane for each pull and kill attempt that lasts longer than this.
There are three sources of the Tunarian Wolfsbane:
Players can receive it as a quest reward from the last quest in the Tunare Deity Quest Line Faith. You will receive one wolfsbane, and this can not be repeated.
Groups defeating Wuoshi will find five Tunarian Wolfsbanes. This can be repeated.
Groups defeating Malkonis D'Morte will get three Tunarian Wolfsbanes. This can be repeated.