https://youtu.be/e8hFCFHjMXQ
In low dosages of a few grams of leaf, kratom functions primarily as a stimulant, with effects similar to caffeine without the marked jitteriness of drinking several cups of coffee. In higher dosages, kratom functions as a neurological opiate, triggering the mu opiate receptors in the brain, even though kratom is chemically different from the opium derived medications such as codeine, morphine, hydrocodone, and oxycodone. Source