The bark of the elfbark tree is used to make hypnotic tea. It is also a drug. Using it can suppress your skill, causing headaches. Chade had a lot of skill headaches after his injury, so he dosed himself very rarely. Maybe this is why he was getting slow? He was probably a bit depressed, and not knowing about the effects of elfbark made it worse.
Elfbark is the bark of a tree.
The bark of a tree is often used to make hypnotic tea. It is harvested by clipping the new branch tips of a tree without breaking them off, a technique known as brutting. Once a fresh twig has been cut from a tree, the ends of it are twisted into a tight cylinder and then placed in a pouch for safe storage until they dry sufficiently to be grated into a powder or infused as a tea.
This process can be repeated several times to obtain a larger quantity of elfbarking.com which is then sifted into a fine powder and stored in a similar fashion. This powder is then strained and drunk to produce an elven-like hypnotic tea. This can be a useful tool for those who wish to improve their Wit in Chalced, as it will suppress any skill headaches that may occur and strengthen their ability to perform a Skill.
It is a drug.
Elfbark, also known as delventree bark, is a potent stimulant. However, it also makes the user prey to feelings of despondency and fearfulness, making them suspicious and defensive even with their closest companions. It is addictive, even when taken sporadically.
This is why it is often used by slave-owners in Chalced to increase the hours that a slave can work while at the same time dampening their spirit. It is not uncommon for slaves to take elfbark, especially when they have been mistreated by their owners.
Fitz uses elfbark to dull his Skill-hunger and to help with the Skill-headaches that come with it, but he doesn’t really use it regularly after his injury. Chade, on the other hand, does seem to use it to help with his Skill-headaches, but he does not use it very often. Perhaps this is because of the effect it has on his ability to Skill. But Kettle prepares more elfbark for him, hoping it will quell the Skill-attacks that are tearing through his mind.