"kratom alkaloids do have opioid activity, but not all; and the most abundant alkaloid, mitragynine, acts on multiple receptors, including those unrelated to the opioid system."

https://marylandopioidresearch.com/home/2686-2/#:~:text=As%20noted%20earlier%2C%20some%20kratom,a%20linear%20dose%20response%20curve.