Kratom, Mitragyna speciosa Korth., is an indigenous tree of lowland forests of southeast Asia. The leaves were used in folk medicine against different ailments including hypertension, diarrhea, cough, and fever. Due to opioid-like effects, kratom has a longstanding history in southeast Asian countries such as Thailand or Malaysia. Its fresh leaves are used as infusion or just chewed for their stimulant properties. Phytochemical analysis led to the isolation of several indole alkaloids, e. g., mitragynine. Further constituents are flavonoids, caffeic acid derivatives, monoterpenoids and triterpenoid glycosides. Modern in vitro assays demonstrated the interaction of kratom alkaloids with opioid receptors. In animal models, antinociceptive and antidepressant/anxiolytic properties have been found. However, clinical studies proving the efficacy of kratom leaves are still lacking. © 2023 The authors.