EXOTIC METHODS
Walkthrough
In the Royal Palace of Orzammar, the very room which was formerly used by King Endrin's middle child. Lady Brodens has been poisoned and an antidote must be found. To finish this quest, a party member must be a master herbalist.
Speak to Herbalist Widron (Orzammar Royal Palace Map, L2) to acquire the quest. Once it is accepted, enter the herbalism screen to craft a potion.
Crafting the Dwarven Regicide Antidote requires Master Herbalism and the following ingredients:
x4 Elfroot
x2 Lifestone
x1 Flask
x2 Concentrator Agent
All the ingredients can be purchased at Figor's Imports. Once the antidote has been made, speak with the sick dwarf (Lady Brodens) to give her the potion and complete the quest.
Note: If you side with Prince Bhelen Aeducan (covertly or not) during the throne ascension, it will grant you access to Lady Brodens' chamber much quicker than choosing to exclusively help Lord Harrowmont.
Rewards
150 XP
The recipe can create potions that cure Sleep and Paralysis (though it is impossible to drink potions while under the effects of either Sleep or Paralysis).
Notes
If you side with Harrowmont in the struggle for the crown, the Royal Quarters are locked and inaccessible until you complete A Lord's Trust/A Prince's Favor: The Second Task.