Willingness to Use Fentanyl Test Strips among Street Drug Users in Puerto Rico: A Cross- Sectional Study

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. However, little is known about their acceptability among street-recruited drug users outside of recreational or clinical contexts. 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. Descriptive statistics, bivariate tests of independence, logistic regression, and Bayesian Model Averaging (BMA) were used to assess associations. Bayes factors were calculated to complement bivariate interpretations. 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 with willingness (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 of association across models. Bayesian analysis confirmed the robustness of treatment engagement and SUD as key predictors. Conclusions Willingness to use FTS is high among Puerto Rican street drug users, especially among those engaged in substance abuse treatment. However, lower willingness among individuals with severe SUD 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. Trial Registration Not applicable