Krathom is mainly used by adults and the elderly. The age of first use for most krathom users was in their late 20s. At the time of this study most users were middle-aged or elderly. Sixty-one percent of regular users of krathom and 12 percent of occasional users believed they were dependent, with reasons for this belief including an inability to quit, a need to use it every day in order to work normally, and a strong desire for krathom when they were not using it. Seventeen percent of all users experienced constipation related to krathom use. Thirty-two percent had at some time felt intoxicated by krathom, having symptoms of fatigue, shaking hands, and headaches. Some users emphasized that these symptoms occurred only when they were unaware of or failed to follow correct methods for using the drug. Users' perceived benefits of krathom were being able to work longer and with more energy, feeling happy/sprightly, maintaining a good mood, sleeping soundly, and being healthy. The percentage of users who reported negative effects of using krathom was comparatively low (4-14 percent of all users). The weight of evidence obtained from this study and previous studies is insufficient to support these beneficial effects of the drug. Additional research is needed on the advantages and disadvantages of krathom use and prevention measures. The study surveyed 149 long-term regular users (daily use for 5 years or longer), 168 occasional users (used only in social situations or medicinally, less than once a week), and 116 nonusers from 3 rural villages in southern Thailand where krathom use was traditional. 2 tables, 2 figures, and 26 references