The coronavirus disease 2019 (COVID-19) pandemic has been assumed to impact patients diagnosed with alcohol use disorder (AUD). The severity of the influence that the COVID-19 pandemic had on the symptoms of AUD has not yet been revealed in detail. The aim of this study was to examine the impact of the COVID-19 pandemic on patients diagnosed with AUD. This retrospective study was conducted between 11 March 2017 and 31 May 2022 in Hungary. Medical charts (N = 1082) of inpatients with the diagnosis of AUD were reviewed. Based on the dates of admissions, two groups were created: the ‘before COVID-19’ group (11 March 2017–10 March 2020) and the ‘during COVID-19’ group (11 March 2020–31 May 2022). Chi-square tests, independent-sample t-tests, and multinomial logistic regressions were performed. The occurrence of delirium tremens (DT) and psychiatric co-morbidities was significantly higher during the pandemic. Our results showed that the occurrence of DT and psychiatric co-morbidities significantly increased during the pandemic. Our results revealed that the pandemic enhanced the severe consequences of AUD, and the development of AUD might have increased in frequency among individuals previously diagnosed with mental illness during the pandemic. These findings indicate the significance of dual disorders in the post-pandemic period.