Pandemic and the globally applied restriction measures mainly affect vulnerable population groups, such as patients with opioid use disorders. Towards inhibiting SARS-Cov-2 spread, the medication-assisted treatment (MAT) programs follow strategies targeting the reduction of in-person psychosocial interventions and an increase of take-home doses. However, there is no available instrument to examine the impact of such modifications on diverse health aspects of patients under MAT. The aim of this study was to develop and validate the PANdemic Medication-Assisted Treatment Questionnaire (PANMAT/Q) to address the pandemic effect on the management and administration of MAT. In total, 463 patients under ΜΑΤ participated. Our findings indicate that PANMAT/Q has been successfully validated exerting reliability and validity. It can be completed within approximately 5 min, and its implementation in research settings is advocated. PANMAT/Q could serve as a useful tool to identify the needs of patients under MAT being at high risk of relapse and overdose.