Cocaine

Cocaine is an alkaloid, usually extracted from the Erythroxylum coca plant. It is a strong stimulant most frequently used as a recreational drug, but it also has some medical use. Overdoses may cause abnormally high body temperature and a marked elevation of blood pressure, which can be life-threatening, abnormal heart rhythms, and death.

Characters poisoned with cocaine

 * Nick Buckley - Peril at End House (self-inflicted, and later probably suicide)
 * Coco Courtenay - The Affair at the Victory Ball

Characters who are cocaine addicts

 * Freddie Rice - Peril at End House