Kratom (Mitragyna speciosa) is a medicinal leaf harvested from a large tree native to Southeast Asia in the Rubiaceae, first documented by Dutch colonial botanist Korthals. It is botanically related to the Corynanthe, Cinchona and Uncaria genii 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.

It is a well established psychoactive drug in its native region and there is some use elsewhere in the world. In Southeast Asia the fresh leaves are usually chewed, often continuously, by workers or manual laborers seeking a numbing, stimulating effect. Elsewhere, the leaves are often made into a tea 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, and 7-hydroxymitragynine, (7-OHM) which is currently the most likely candidate for the primary active chemical in the plant. Although structurally related to yohimbine and tryptamines, its pharmacology is quite different, acting as a potent mu-opioid receptor agonist. (7-hydroxymitragynine has antinociceptive effects with 17X the potency of morphine due entirely to its action on opioid receptors.) [1] Anectotal evidence supports that it may have some stimulant properties similar to yohimbine. Kratom users have described feeling alternatively stimulated then sedated over the course of several hours of use. Kratom also contains alkaloids found in uña de gato, which are powerful immune system enhancers and lower blood pressure, as well as epicatechin, a powerful antioxidant 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 alkakoids such as corynantheidine.

Kratom has many potential medicinal uses, including as a safer and cheaper replacement for methadone, and as a source of chemicals with a wide range of beneficial activities.