Mitragyna speciosa (also known as kratom) is a tropical tree of the coffee family indigenous to South East Asia. The leaves of M. speciosa contain various psychoactive alkaloids that produce mild stimulant and opioid effects. The pharmacology of kratom is complex, although it produces its major effects through action at opioid receptors in the brain.

M. speciosa is indigenous to Thailand, Indonesia, Malaysia, Myanmar, and Papua New Guinea, where it has been used in traditional medicines for centuries. Traditionally, fresh or dried kratom leaves are chewed or made into tea. Starting in the 2000s, kratom began to receive significant attention due to increased use in Western cultures as an alternative medicine. It is readily available for purchase from a large number of internet vendors, most commonly as dried and powdered leaves.

People reports indicate that the effects of kratom vary depending on the dose used. Lower doses are reported to produce a caffeine-like stimulant effect. Higher doses produce opioid effects like pain relief, sedation, and euphoria. Many users claim kratom is useful in treating opioid addiction as a weaning agent, particularly during the initial withdrawal phase. Kratom exists in a variety of strains with different characteristics, some more opioid-like than others.