Syringe service program leader and participant perspectives on reasons for opioid-stimulant co-use in the United States.

Background: Opioids and stimulants are increasingly used together in North America. Using syringe service program (SSP) leaders' and participants' perspectives, we sought to identify reasons for intentional and unintentional co-use. Methods: We used a sequential exploratory mixed method design with interviews and a questionnaire of SSP leaders and participants in the U.S. between 2022 and 2024. We recruited a national sample of SSP leaders for telephone/virtual interviews, stratifying for counties with higher overdose rates, higher percentages of non-white residents, and geographic variation. We asked SSP leaders to share flyers with their SSP's participants. We analyzed qualitative data using iterative categorization and developed an online quantitative questionnaire based on qualitative findings. We disseminated the questionnaire to all SSP program leaders listed on a public website of SSPs in the U.S. and asked them to share it with their SSPs' participants. We analyzed quantitative data using descriptive statistics and chi-square tests. Results: Individuals (n = 30) from 13 U.S. states completed interviews, indicating the following reasons for co-use: seeking enhanced euphoria, unintentional co-use due to adulteration, staying awake part of the day and sleeping during the other part, using any drug available, perceived health benefits, and balancing effects for a comfortable experience. Individuals (n = 171) from 45 states and Washington, D.C. completed the quantitative questionnaire. Enhanced euphoria was the most frequently perceived reason for co-use (indicated by 67 % of respondents), with no significant differences in reasons for use by region. Discussion: Co-use is often intentional. SSPs should address risks through education.