The kratom (Mitragyna speciosa) is a 4 to 16 metre high tropical tree indigenous to South East Asia, the Philippines and New Guinea but now cultivated elsewhere. Traditionally, fresh or dried kratom leaves are chewed or made into tea; they are seldom smoked. At a low dose, kratom has stimulant effects and is used to combat fatigue during long working hours. At high dosages, however, it can have sedative-narcotic effects. It is also used in traditional medicine and as an opium substitute. The main psychoactive components in the leaves are mitragynine and 7-hydroxymitragynine, both found only in Mitragyna speciosa.