This study describes patterns and consequences of chewing leaves of krathom, Mitragynine speciosa, Kroth., traditionally used by rural people in Thailand as a mild narcotic. We surveyed 149 long-term regular users (daily for >or= 5 years), 168 occasional users (used only in social situations or medicinally, less than once a week), and 116 nonusers from three rural villages where krathom use was traditional in southern Thailand. Users focused on the perceived advantages of krathom in relation to increased work endurance, medication, and as a substitute for other hard substances rather than its harmful effects. Limitations regarding self-report and generalizability of the study were noted, and further longitudinal study among other population groups is required for educating people and users about possible harmful impacts of krathom use.