The pandemic crisis and the restriction measures applied detrimentally affected several aspects of life of patients under medication for addiction treatment (MAT), potentially influencing the management and administration of methadone and buprenorphine. In total, 444 patients were divided into two groups based on medication and completed an anonymous self-reported Pandemic Medication-Assisted Treatment Questionnaire (PANMAT/Q) to assess the impact of the COVID-19 pandemic on the management and administration of MAT. The findings revealed that “Mood”, “Sociability”, and “Substitute administration and pandemic measures” were affected more in patients taking methadone than in those taking buprenorphine. The variables, namely, “Age”, “Place of residence”, “Years attending MAT”, “Living in high-risk area for SARS-CoV-2 infection” and “Educational status”, were correlated with the dimensions “Mood” and “Sociability”, affecting the substance administration context. Sociodemographic variables play a key role in retention in treatment and prevention of drug-seeking behavior, influencing dimensions that mediate the management and administration of MAT during the pandemic outbreak.