This randomized Type 1 hybrid effectiveness-implementation trial (N=186) will evaluate the effectiveness and implementation of a peer-delivered problem solving and behavioral activation intervention for adherence to LAI-PrEP/ART ("Peer Activate-LAI") compared to enhanced treatment as usual (ETAU) for a largely Black, substance-using population living with or at high risk for HIV. Specific aims are to:

Aim 1: Evaluate the effectiveness of Peer Activate-LAI over 12-months on: a) LAI-PrEP/ART adherence (primary; receipt of all 6 maintenance injections within 7-day window); and b) substance use (secondary; WHOASSIST, urine toxicology); and c) Explore the moderating role of SRD-related factors (exploratory)

Aim 2: To evaluate the implementation of Peer Activate-LAI including feasibility, acceptability, fidelity, and adoption guided by RE-AIM and Proctor's model,12,13 assessed using mixed methods, including a rapid ethnographic assessment of how SRD-related factors may affect implementation.

Aim 3: To evaluate the economic viability of Peer Activate-LAI, including a) cost of implementation and sustainment, and b) cost-effectiveness from multiple stakeholder perspectives.

This study will inform a potentially scalable, cost-effective model for facilitating effective adherence to LAI formulations of PrEP/ART within Black, substance-using populations with multiple minority identities who to date have had limited support for improving LAI adherence for HIV treatment and prevention.

Background. Substance use continues to be a major driver of HIV acquisition and has been associated with suboptimal ART adherence, treatment interruption, and inability to achieve or maintain viral suppression. Use of PrEP, a key tool for HIV prevention, is disproportionately lower in racial/ethnic minorities, as well as people who inject drugs. Factors related to structural racism and discrimination (SRD) may contribute to low rates of adherence in these populations. New long-acting injectable (LAI) formulations of PrEP/ART provide a potential biomedical intervention to overcome adherence challenges, however, due to the prolonged subtherapeutic period after LAI discontinuation, ensuring adherence is crucial.

A peer-delivered reinforcement-based intervention may be a promising solution for improving LAI adherence. Our team has developed through several rounds of stakeholder feedback a peer-delivered behavioral activation and problem-solving intervention, Peer Activate. Peer Activate focuses on problem-solving skills to improve adherence to ART and/or PrEP both at the individual level and social/structural barriers to care (i.e., transportation, housing) and includes behavioral activation to promote engagement in rewarding, substance-free activities in one's environment and structured daily activities to promote treatment adherence. Delivery by a peer with formal training and shared lived experiences enhances the impact of the intervention on SRD-related factors. However, Peer Activate has not been evaluated in the context of LAI PrEP/ART.

Preliminary Studies. This proposal builds upon our team's prior studies demonstrating 1) our ability to engage patients with and at risk for HIV, facing multiple barriers due to SRD, and provide LAI PrEP/ART in community-based settings; 2) the feasibility and acceptability of Peer Activate and promise in improving HIV treatment adherence for people who use substances.; and 3) promise for cost-effectiveness.

Approach. We propose a randomized Type 1 hybrid effectiveness-implementation trial (N=186) to test the effectiveness and implementation of Peer Activate for LAI PrEP/ART ("Peer Activate-LAI") vs. enhanced treatment as usual for a predominantly Black substance using population living with or at high risk for HIV, evaluating the following over 12 months:

1. effectiveness: a) LAI PrEP/ART adherence (primary; receipt of all 6 maintenance injections within 7-day window); b) substance use (secondary; urine toxicology, self-report); c) SRD as moderators of effectiveness (exploratory);
2. Implementation of Peer Activate-LAI including feasibility, acceptability, fidelity, and adoption guided by RE-AIM and Proctor's model,9,10 assessed using mixed methods, including a rapid ethnographic assessment of how SRD-related factors may affect implementation; and
3. Economic viability of Peer Activate-LAI, including cost of implementation and sustainment and cost-effectiveness from multiple stakeholder perspectives. Implications.

This study will inform a potentially scalable, cost-effective model for facilitating effective adherence to LAI formulations of ART/PrEP within Black, substance using populations who to date have had limited support for improving LAI adherence for HIV ART/PrEP.

Inclusion Criteria:

• Age 18 years or older
• Able and willing to sign informed consent
• HIV status:

HIV negative with a negative HIV antibody/antigen test and meeting CDC(center for disease control and prevention) criteria for PrEP HIV positive with a positive antibody/antigen test

• Meeting indications for treatment based on Cabotegravir-LA (HIV negative) or Cabotegravir (CAB) and Rilpivirine (RPV)-LA (HIV positive) prescribing information
• Moderate substance use, defined as a (World Health Organization Alcohol, Smoking and Substance Involvement Screening Test) WHO-ASSIST score of ≥4 for certain drugs (cocaine, amphetamines, inhalants, sedatives, hallucinogens, or opioids) or ≥11 for alcohol

Exclusion Criteria:

• Contraindications to Cabotegravir-LA (HIV-) or Cabotegravir (CAB) and Rilpivirine (RPV)-LA (HIV+) use based on prescribing information or other medical/psychiatric conditions that may interfere with study participation
• Pregnant or breastfeeding