The goal of this observational clinical study is to is to learn more about how commercial kratom products affect healthy adults who consume them regularly. The main questions it aims to answer are:

1. What are the acute physiological, subjective, and cognitive effects of kratom following participant self-administration of a single oral dose of the participants usual kratom product at the participants typical dose?
2. What are the physiological, subjective, and cognitive effects associated with kratom product discontinuation among adults who use regularly?
3. What are the pharmacokinetics of kratom products consumed by adults who use regularly? On the first study day: Under direct observation, participants will self-administer a single oral dose of the participants own commercial kratom product that that is regularly taken and will consume it at the participants self-selected typical dose/serving. Following this, serial blood draws and urine collection will occur along with administration of validated questionnaires, tests, and continual monitoring. After this first study day, participants will no longer be permitted to use any of the participants kratom product during the study. On study nights/days 2-3: participants will reside a clinical research unit and be observed and evaluated for kratom withdrawal syndrome.

INCLUSION CRITERIA:

1. >21 years
2. reporting kratom use >5 times per week for >3 months prior to study screening
3. English language proficiency
4. Willingness to provide requested samples of the kratom product being currently taken

EXCLUSION CRITERIA:

1. Reports any acute adverse, unexpected, or otherwise sudden health event related to the typical kratom product dose that occurred within 30 days of screening
2. Having ever sought medical attention for an acute adverse health event as a result of taking any kratom product.
3. Cannot or will not provide kratom product samples in the form of an unopened package of kratom that is clearly labeled with at least the product and vendor name.
4. Self-reports using kratom products by any other route than orally swallowing.
5. Current physical dependence on alcohol, benzodiazepines, or opioids
6. Reports use of fentanyl within the past month and/or has a fentanyl positive drug screen.
7. Discordance between self-reported substance use and drug screen results obtained during screening.
8. Lifetime or current psychotic disorder
9. Current untreated major depressive or bipolar disorder
10. Pregnancy or nursing
11. Physical, psychiatric, or environmental conditions considered by study team to increase risk or undue burden (e.g., untreated hypertension, high BMI, etc.).

Healthy adults aged 21 or older who use kratom.