In the present study, we described temporal trends in inpatient care use due to common adult mental disorders in Czechia in the time period from 1994 to 2015. Overall, the admission rates remained relatively unchanged in seniors, slightly increased in adults, whereas adolescents and emerging adults demonstrated a more profound increase. We demonstrated that the median LOS for adult mental disorders was decreasing, except for male adolescents and emerging adults who showed stable levels in time. Taken together, trends in admission rates and median LOS suggest that inpatient episodes for adult mental disorders have become more frequent and shorter over time. Then, the overall use of inpatient care, as assessed by SIY, showed reductions in adults, unchanged levels in seniors and male adolescents and emerging adults, but an increase in female adolescents and emerging adults. These findings are broadly in line with the observed trends in many Western countries in the last decades of the 20th century and the beginning of the 21st century [31,32,33,34,35].

Several mechanisms, most likely interacting with each other, may be responsible for the observed trends. First, notable changes in the provision of inpatient care occurred. Given the high costs of psychiatric hospitalizations [21] and deinstitutionalization trends elsewhere in Western Europe [31,32,33,34,35,36,37], the observed trends might have been caused by a growing policy emphasis on reductions of long-term hospitalizations, increased tendency towards cost-effectiveness, and changes in reimbursements. The number of beds in psychiatric hospitals was decreasing in Czechia, with 99 beds per 100,000 inhabitants in 1997 and 81 beds per 100,000 inhabitants in 2015 [45]. Moreover, the bed occupancy rates increased from 88.0% in 2000 to 93.3% in 2015 [45]. This suggests increasing pressure on effective resource utilization, thus possibly incentivizing clinicians to prefer earlier discharges or zero-day hospitalizations and to favour admissions for certain conditions.

Second, the number of outpatient psychiatrists per 100,000 inhabitants rose from 4.96 in 1996 to 8.30 in 2015 [45], potentially permitting a reduction in the length of hospitalization by enhanced aftercare. Also, the reductions in inpatient service use in people with schizophrenia might be related to the introduction of novel psychopharmacological treatments, such as atypical antipsychotics and long-lasting depot injections, which make outpatient treatment more feasible. Although we do not have data on trends of antipsychotic drug use in Czechia over the past decades, some evidence suggests significant increases in overall prescription drug expenditures over time concurrent with decreases in inpatient expenditures [55]. Next, antidepressant drug consumption in Czechia witnessed one of the largest increases in Europe between 2000 and 2015 [56]. Although this increase may, in part, reflect more overuse and off-label use [57], it is also likely to represent the aftercare of discharged hospital patients.

Third, societal changes brought on by the transition from a one-party political system and a centrally organized economy to an elected, capitalist democracy, need to be considered. This transition led to previously unknown societal challenges, including unemployment, that likely contributed to worsened mental health outcomes of the population in the 1990s. Similarly, after a period of relative obscurity before the Velvet Revolution, there was a profound increase in the availability of psychoactive substances in the 1990s transition period, leading to elevated levels of drug and alcohol use [58], and, consequently, to potential mental health harms associated with the use of these substances.

Additionally, other factors shared across the Western world, including (a) increased awareness about mental health and greater acceptance of professional help for mental health problems [59], (b) changes in the underlying population of people with mental disorders, particularly for internalizing disorders in female adolescents [60], and (c) the gradual proliferation of e-mental health and self-help services might have played a role.

The allocation of resources did not seem to follow the patient discharges from inpatient care, with the financing of the outpatient sector remaining relatively stable, accounting for 15.3% and 14% of the mental health care budget in 2006 and 2015, respectively [42, 43]. A qualitative study investigating general practitioners’ and outpatient psychiatrists’ needs found that outpatient services are overloaded [61]. Moreover, community-based care remained to be insufficiently deployed in Czechia in the past decades, with services such as mobile crisis teams, day clinics, and residential housing remaining largely inaccessible due to low numbers and uneven distribution across the country [44]. Furthermore, in a treatment satisfaction study, only half of patients discharged from inpatient services obtained information on where to turn in case of additional health issues and/or other problems [44], suggesting a lack of patient monitoring and low implementation of integrated community care [62].

The number of people with schizophrenia treated in the outpatient sector demonstrated only a limited increase despite decreases in inpatient care use [45], raising concerns about the adequacy of provided care and assistance. Given the lack of community-based alternatives and the overloaded outpatient sector, the group of people with severe mental illnesses such as those with schizophrenia might have experienced an overall reduction in care upon their discharge, possibly deepening the existing treatment gap in Czechia [63]. Moreover, 14.9% of long-stay patients with psychosis in Czechia were shown to be re-hospitalized within 2 weeks after discharge from inpatient care [24], suggesting the presence of a revolving-door phenomenon. While the subsequent therapeutic pathways of the discharged individuals in Czechia are largely unknown, these issues are of serious concern and warrant further investigation.

The present study has some limitations. First, in some mental disorders, a number of age and sex combinations contained excessive zero counts (e.g., eating disorders in males), and we cannot rule out the possibility that we did not capture the magnitude of temporal trends optimally in these instances. In future investigations, segmented zero-inflated models might be more appropriate when the primary research interest lies in estimating temporal trends in strata with such rare outcome occurrences [64]. Second, mental disorders can also be listed as secondary diagnoses; however, we restricted our analyses to those listed as primary diagnoses. We did so to capture the actual cause of the inpatient stay, but we cannot rule out the possibility that some mental disorders were systematically more or less likely to be listed as the primary diagnosis throughout the studied time period. Third, in some instances, we found considerable age-specific heterogeneity in time trends; thus, a more fine-grained assessment considering age-specific developments (e.g., in older adolescents) is warranted. Fourth, in a number of European countries, there has been a broad trend of moving away from psychiatric hospitals as the dominant institutions, with general hospital-based mental health services growing in importance [10]. However, we did not distinguish between hospitalizations in general hospitals’ psychiatric wards and psychiatric hospitals, thus possibly masking differential patterns in time trends. Finally, although the ICD-10 taxonomy was used throughout the whole observation period, changes in recording and diagnostic practices may undermine the temporal consistency of the psychiatric diagnoses, biasing the identified time trends. However, we are not aware of research indicating significant confounding factors in diagnostic practice over the time period of this study.