In view of disease-related threats, containment measures, and disrupted healthcare, individuals with pre-existing mental illness might be vulnerable to adverse effects of the COVID-19 pandemic. Previous reviews indicated increased mental distress, with limited information on peri-pandemic changes. In this systematic review, we aimed to identify longitudinal research investigating pre- to peri-pandemic and/or peri-pandemic changes of mental health in patients, focusing on the early phase and considering specific diagnoses. PsycINFO, Web of Science, the WHO Global literature on coronavirus disease database, and the Cochrane COVID-19 Study Register weresearched through 31 May 2021. Studies were synthesized using vote counting based on effect direction. We included 40 studies mostly from Western, high-income countries. Findings were heterogeneous, with improving and deteriorating mental health observed compared to pre-pandemic data, partly depending on underlying diagnoses. For peri-pandemic changes, evidence was limited, with some suggestion of recovery of mental distress. Study quality was heterogeneous; only few studies investigated potential moderators (e.g., chronicity of mental illness). Mental health effects on people with pre-existing conditions are heterogeneous within and across diagnoses for pre- to peri-pandemic and peri-pandemic comparisons. To improve mental health services amid future global crises, forthcoming research should understand medium- and long-term effects, controlling for containment measures.

Background: The COVID-19 pandemic presented significant challenges to infectious disease management and mental health services (MHS). Service demand and delivery changed due to fear of infection, economic hardships, and the psychological effects of protective measures. This systematic review with meta-analysis aims to quantify these impacts on different mental health service settings. Methods: Comprehensive searches were conducted in PubMed, Embase, and PsycINFO, focusing on studies published from the initial outbreak of COVID-19, starting in November 2019. Studies were included comparing the utilization of mental health inpatient, emergency department (ED), and outpatient services (including telemedicine and medication prescriptions) before and during the COVID-19 pandemic. A random-effects model was employed to estimate pooled effects, with study quality assessed using a modified Newcastle-Ottawa Scale. Results: Among 128 studies, significant decreases in utilization were observed during the initial phase of the pandemic for inpatient services (RR: 0.75, 95% CI: 0.67 to 0.85) and ED visits (RR: 0.87, 95% CI: 0.69 to 1.10). Outpatient services showed a similar decline (RR: 0.78, 95% CI: 0.66 to 0.92), while no significant change was found in psychotropic medication prescriptions (RR: 0.90, CI: 0.77 to 1.05). In contrast, telemedicine utilization increased significantly (RR: 7.57, 95% CI: 3.63 to 15.77). Conclusions: The findings reveal substantial shifts in mental health service utilization during the pandemic, with the largest reductions in inpatient services and significant increases in telemedicine use. These results emphasize the need for flexible healthcare models. Further research is essential to evaluate the consequences of reduced MHS utilization.