PROJECT SUMMARY/ ABSTRACT Women who inject drugs (WWID), especially those engaging in sex work, bear a disproportionate burden of new HIV infections. While WWID would benefit from woman-controlled HIV prevention strategies, such as pre- exposure prophylaxis (PrEP), they have been underrepresented in all phases of PrEP research and uptake remains low. The goal of this randomized controlled trial (RCT) is to test the efficacy of a trauma-informed expressive writing (EW) intervention for boosting the effectiveness of contingency management (CM) to reduce HIV acquisition risk in WWID who initiate pre-exposure prophylaxis (PrEP). The rationale is that EW+CM will address the intersection of trauma, substance use, and suboptimal PrEP adherence to achieve more durable reductions in HIV acquisition risk (i.e., the co-occurrence of HIV risk behaviors and PrEP non-adherence). This RCT will leverage our longstanding partnership with Prevention Point Philadelphia. WWID who are at risk for HIV (e.g., report syringe sharing or condomless sex and no PrEP use within 30 days) and interested in PrEP will be linked to PrEP care at Prevention Point. A cohort of 360 WWID who initiate PrEP will be enrolled and immediately begin a 3-month CM period that includes daily directly observed PrEP doses, stimulant/opioid abstinence (measured thrice weekly through urine screening), and 4 writing sessions. After a run-in period, women will be randomized to one of two study arms: EW+CM (n=180) or Neutral Writing+CM (n=180). Follow- up assessments will be conducted at 3, 6, and 12 months post-randomization and will include collection of scalp hair to quantify monthly levels of tenofovir, an objective metric of PrEP adherence. The specific aims of this RCT are to: (1) Determine the efficacy of EW+CM for improving the proportion of participants achieving reductions in HIV acquisition risk (operationalized as the proportion of WWID reporting syringe sharing or condomless sex during objectively measured periods of PrEP non-adherence) at 12 months. (2) Examine key secondary outcomes such as greater PrEP persistence, reductions in substance use, PTSD symptoms, depression, entry into drug treatment, and cost-effectiveness over 12 months. (3) Evaluate mediating pathways through which the intervention operates (e.g., mediated by reductions in substance use or emotional expression and processing in EW essays) and moderators of these relationships (e.g., more pronounced among those with higher PTSD severity at baseline). This RCT could have exceptional impact by yielding one of the first evidence-based interventions to address HIV acquisition risk in the era of PrEP among WWID. It is highly innovative to integrate this gender-specific RCT into known and needed community-based SSP services and to include a robust cost-effectiveness analysis to guide implementation and scale up should EW+CM be efficacious. The long-term outcome of this research program will be a reduction in HIV through a replicable model that that optimizes PrEP engagement among WWID.

PROJECT NARRATIVE Women who inject drugs (WWID) are disproportionally impacted by HIV across settings. Pre-exposure prophylaxis (PrEP) is one of few female-driven methods that safely and effectively reduces risk of HIV acquisition, yet interventions to optimize PrEP engagement among WWID are scant. This randomized controlled trial will test the efficacy of a trauma-informed expressive writing intervention for boosting the effectiveness of contingency management to reduce HIV acquisition risk in WWID who initiate PrEP.