This study aims to quantitatively and qualitatively investigate the consequences of the infiltration of prohibited items, particularly narcotics, into Iranian prisons and to propose strategies for controlling and reducing their transfer. Employing a mixed-method approach, the research focused on prisons in western Iran. Through convenience sampling, five provinces—Kurdistan, Ilam, Hamedan, Kermanshah, and West Azerbaijan—were selected. A sample of 242 prisoners was chosen using stratified random sampling based on Cochran’s formula, proportional to the prisoner population reported by the Prison Organization. Data were collected via a researcher-designed questionnaire. Quantitative findings revealed that the entry, distribution, and use of prohibited items in the studied prisons are associated with extensive negative emotional consequences, including anxiety, stress, chronic fear, insecurity, sadness, depression, hopelessness, suicidal ideation, and attempts, as well as offers to collaborate in smuggling, distributing, and consuming these items. Qualitative results identified key reasons for the infiltration of prohibited items, including organized criminal networks, weak regulations, profitability of drug smuggling, and inadequate control and inspection facilities. Proposed solutions were categorized into four groups: cultural factors (e. g., prisoner employment and recreation), control and monitoring policies, managerial factors, and legal and regulatory measures. The findings indicate that the presence of narcotics in prisons has profound negative impacts on both prison staff and inmates across various dimensions.