Co-occurring substance use disorders and the compounding effect of kratom on serious mental illness, US, 2021-2023

Background: Kratom's rise in popularity during multiple overlapping drug use crises is potentially driving poor mental health outcomes and straining health systems.Objective: To investigate temporal changes in the compounding effect of kratom on serious mental illness (SMI) when co-used with other drugs.Methods: We used the National Survey of Drug Use and Health (2021-2023; N = 139,524; male n = 61,926; female n = 77,598) to identify SMI, a range of drug use disorders (SUD), and kratom use. Our focal predictor was whether an individual had 1) no SUD and no kratom use, 2) an SUD without kratom, 3) kratom use without an SUD, or 4) both an SUD and kratom use. We used multiple logistic regression to model whether SMI is associated with SUD/kratom status, year, and their interactions.Results: Roughly 6% of adults met the criteria for SMI. We found that the increase in SMI over 3 years was fastest and markedly different among those with both OUD and kratom use, such that the predicted SMI prevalence went from 20% in 2021 to 50% by 2023 (interaction p = .01), whereas SMI remained relatively stable for other drug combinations, including those with OUD without kratom use, kratom without OUD, and neither OUD nor kratom.Conclusion: Over a short period of 3 years, SMI more than doubled among those with concurrent kratom use and OUD. At a time of strained US treatment systems, high overdose rates, and a mental health crisis, we stress the multiplicative association between kratom, opioid use disorder, and SMI.