Abstract
BACKGROUND: Fentanyl contamination in illicit drug markets has significantly increased overdose risk in Puerto Rico and other regions. Fentanyl test strips (FTS) have emerged as a promising harm reduction tool. While several studies in the United States have examined FTS willingness and acceptability, research in Puerto Rico remains scarce. This study offers one of the first large-scale epidemiological assessments of willingness to use FTS among street-recruited drug users on the island. METHODS: We conducted a cross-sectional study of 400 street drug users recruited from syringe exchange programs in Puerto Rico between March and June 2024. Participants completed structured interviews assessing sociodemographic characteristics, substance use behaviors, overdose history, and program engagement. Willingness to use FTS was measured through a direct question and coded as a binary variable. Analyses included descriptive statistics, bivariate tests of independence, Bayes factors, logistic regression, and Bayesian Model Averaging (BMA). RESULTS: Overall willingness to use FTS was high (76.5%). Engagement in substance abuse treatment was strongly associated with willingness (OR = 3.09, 95% CI: 1.81-5.26, p < 0.001; Bayes Factor = 336.17). In contrast, severe substance use disorder (SUD) was negatively associated (OR = 0.36, 95% CI: 0.18-0.73, p = 0.005; Bayes Factor = 1.19). Other variables such as age, overdose history, or homelessness showed inconsistent or weak evidence. BMA confirmed treatment engagement (inclusion probability = 100%) and SUD severity (95.4%) as the most robust predictors, while age and other covariates had low inclusion probabilities, suggesting weaker evidence across models. CONCLUSIONS: Willingness to use FTS is high among Puerto Rican street drug users, especially among those engaged in substance abuse treatment. Lower willingness among individuals with severe SUD aligns with patterns reported in prior research, suggesting that higher levels of dependence may limit the perceived feasibility or utility of FTS. This underscores the need for low-threshold, tailored harm reduction strategies. These findings highlight both the promise and challenges of implementing drug-checking interventions in underserved, high-risk populations. As FTS are not currently available in Puerto Rico, expanding access through harm reduction and treatment programs should be a public health priority.