Carris Seed (presumably) comes from a Carris plant. Carris oil can also be extracted from the seeds and has the same effects.
Carris seed in small amounts produces feelings of euphoria, giddiness and a lift in overall mood. When consumed in larger doses Carris seed gives the user great stamina and greater strength than usual by essentially fooling the user's body into ignoring a lack of energy, similar to the effects of Amphetamines or Caffeine in the real world. After the effects of this high ware off, the user often experiences extreme weariness, as their body now realises it has no energy, and is not being "fooled" by the the drug anymore. Extended use can cause the user to become physically frail and unable to perform strenuous manual tasks.
Use and acceptance
Carris seed is often used by travellers to give them stamina or a boost of energy, by scholars to allow them to avoid sleep. Carris seed or oil (an extract from seeds) is sometimes given to a horse or animal of burden to increase performance in manual tasks, if done consistently by an owner this is seen as mistreatment of an animal, though many owners continue the practice anyway. Many merchants and vendors feed Carris seed or oil to horses and other animals prior to attempting to sell them, this is seen as gross malpractice and very dishonest and can be dealt with by authorities in some cases. In horse racing, horses are often given Carris seed or oil prior to a race to increase their energy level and stamina and hence performance in the race, this is seen as mistreatment of the animal by some and certainly cheating, as it provides the horse with an unfair advantage against other horses.