BackgroundWe assessed the moderating effect of pre-pandemic mental disorders on the association of COVID-related perceived stress and social support with mental health.MethodsA nationally representative sample of 3500 Spanish adults was interviewed in June 2020 (mean age 49.25 years, ± 15.64; 51.50% females). Mental health included Generalized Anxiety Disorders (GAD; GAD-7, cut-off point of ≥ 10), Major Depressive Disorders (MDD; PHQ-8, cut-off point of ≥ 10) and the comorbid form (those screening positive for GAD and MDD). COVID-related stress was assessed using an adapted version of the Peri Life Events Scale, and social support using the Oslo Social Support Scale. Logistic regression models were used to assess if COVID-related stress and social support were related to mental health outcomes and interactions were conducted to examine whether these relationships differed according to the presence of pre-pandemic mental disorders.ResultsHigher COVID-related stress was associated with a higher risk of lower mental health. The association between COVID-related stress with GAD and MDD was significantly moderated by pre-pandemic mental disorders, except for comorbid GAD + MDD. Higher levels of social support were linked to better mental health. Only the association between social support and GAD was significantly moderated by pre-pandemic mental disorders. That is, for those without pre-pandemic mental disorders, higher levels of social support decreased the odds of GAD, while minor decreases were observed in those with pre-pandemic mental disorders.ConclusionsThe impact of COVID-related stress and social support on specific indicators of mental health may vary depending on the existence of a previous mental disorder.