Kratom (Mitragyna speciosa) is a medicinal leaf harvested from a large tree native to Southeast Asia in the Rubiaceae family, first documented by Dutch colonial botanist Korthals. It is botanically related to the Corynanthe, Cinchona and Uncaria genera and shares some similar biochemistry. It is in the same family as coffee and the psychoactive plant Psychotria viridis. Other species in the Mitragyna genus are used medicinally in Africa, and also used for their wood.
Kratom is used for its psychoactive effects in its native region, with growing use elsewhere in the world. It is grown widely in Indonesia for worldwide trade. In Southeast Asia the fresh leaves are usually chewed, often continuously, by workers or manual laborers seeking a numbing, stimulating effect. Less commonly, the leaves are decocted or extracted into water and then evaporated into a tar that can be swallowed. Kratom is not often smoked, although this method does provide some effect.
Kratom contains many alkaloids including mitragynine (once thought to be the primary active), mitraphylline, and 7-hydroxymitragynine (which is currently the most likely candidate for the primary active chemical in the plant). Although 7-hydroxymitraygynie and mitragynine are structurally related to yohimbine and other tryptamines, their pharmacology is quite different, acting primarily as mu-opioid receptor agonists. Kratom also contains alkaloids found in uña de gato, which are thought to play a beneficial role on the immune system and lower blood pressure, as well as epicatechin, a powerful antioxidant also found in dark chocolate and closely related to the EGCG that gives green tea its beneficial effects. Other active chemicals in kratom include raubasine (best known from Rauwolfia serpentina) and some yohimbe alkaloids such as corynantheidine.