Evaluating a Potential Pharmacokinetic Kratom-oxycodone Interaction Concurrent With Clinical Endpoints

The goal of this study is to investigate whether the botanical product kratom affects how the body processes the opioid drug oxycodone. The main research questions to be answered are two-fold: 1. How does kratom affect the manner in which oxycodone is metabolized (broken down and removed) by the body? 2. Does kratom change the effects oxycodone exerts on the body? Healthy adult participants will complete four study arms, during which they will be given the following: * Kratom (as a tea) * A single dose of oxycodone (as a tablet) * Kratom tea and a single dose of oxycodone * Kratom tea for four days, then kratom tea and a single dose of oxycodone