Background and Objective: The complexity of antiretroviral therapy (ART) regimens in people living with HIV (PLHIV) poses significant challenges for medication management, impacting adherence and overall health outcomes. The Medication Regimen Complexity Index (MRCI) is a tool that quantifies regimen complexity, yet its correlation with hospitalization rates and adverse drug reactions (ADRs) in PLHIV remains underexplored. Materials and Methods: This prospective study, which was conducted at a government-funded antiretroviral treatment center, investigated the relationships among MRCI scores, hospitalization due to ADRs, and the ADR rates in 285 PLHIV participants over 18 months. Results: The study revealed a significant association between higher baseline MRCI scores and hospitalization due to ADRs, with a threshold MRCI score of 8 indicating increased risk. There was no significant association between average MRCI scores and overall ADR rates or non-ADR-related hospitalizations. Conclusions: These findings emphasize the importance of monitoring medication regimen complexity in PLHIV, particularly in the context of preventing hospitalizations related to ADRs. Further research is needed to understand the multifactorial influences on ADR occurrence and to optimize ART regimens for better patient outcomes.