Kratom contains mitragynine and 7-hydroxymitragynine, which act on opioid receptors in the brain, producing effects similar to opioids like morphine. This pharmacological similarity justifies the need for strict control  .

https://www.fda.gov/news-events/press-announcements/statement-fda-commissioner-scott-gottlieb-md-agencys-scientific-evidence-presence-opioid-compounds