Mental Disorders: Prevalence & Unmet Need for Treatment🔗
Mental disorders are one of the leading causes of disability worldwide, affecting 10-19% of all individuals in any given year (Kessler et al., 2009). Overall, one in three people are estimated to develop a mental disorder once in their life (Steel et al., 2014; Chesney et al., 2014; Vigo et al., 2016; Kessler et al., 2009).
Suffering from mental illness is associated with numerous negative outcomes for the individual and society, including labor market marginalization (Niederkrotenthaler et al., 2014, 2016), worse educational attainment (Eisenberg et al., 2009; Hysenbegasi et al., 2005; Kessler et al., 1995), limited role functioning (Fergusson & Woodward, 2002), negative somatic health outcomes (Hare et al., 2014; Wang et al., 2020), as well as early mortality (Cuijpers & Smit, 2002) and suicide (Nock et al., 2009). As a consequence, mental illness causes an enormous financial burden, with global costs adding up to 4.7 trillion dollars per year (Arias et al., 2022). It is estimated that by 2030, depression alone will become the leading cause of disease burden worldwide (WHO, 2011).
There is a range of evidence-based treatments for common mental disorders, including both psychological treatments (e.g., cognitive-behavioral therapies; Carpenter et al., 2018; Cuijpers et al., 2023; Karyotaki et al., 2021; Mendes et al., 2008; Olatunji et al., 2013; Papola et al., 2023) and pharmacotherapy (Cipriani et al., 2018; Leucht et al., 2013).
For depressive disorders, many treatment guidelines recommend combination therapy as a first-line treatment, whereby evidence-based psychological treatment is provided alongside pharmacotherapy (e.g., Bundesärztekammer et al., 2022). In the long run, psychological treatment may be more effective than antidepressants when the two are compared directly (Furukawa, Shinohara, et al., 2021), and newer guidelines reflect this finding (Brohan et al., 2024).
For anxiety disorders, psychological treatments (including exposure-based approaches) are often recommended as first-line treatment (Bandelow et al., 2022; Katzman et al., 2014). For psychotic disorders, pharmacological treatment typically takes precedence, with some psychosocial interventions (e.g., psychoeducation, cognitive-behavioral therapy for psychosis) recommended as part of a holistic intervention concept (Keepers et al., 2020; Hasan et al., 2020).
Despite the availability of effective treatments, the population-level impact of current mental health care is still suboptimal. Evidence-based treatments are established in many health care systems, and the number of patients who receive them has increased in recent decades (De Graaf et al., 2012; Filatova et al., 2019; Jorm et al., 2017; Kessler et al., 2005; Kowitz et al., 2014; Steffen et al., 2020; Walters et al., 2012). Nevertheless, there are no signs that the prevalence of mental disorders has decreased, not even in countries with well-developed mental health infrastructures (Baxter et al., 2014; Bretschneider et al., 2018; Ferrari et al., 2013; GBD 2019 Mental Disorders Collaborators, 2022; Richter et al., 2019; Steel et al., 2014).
Different reasons have been named for this “treatment-prevalence paradox” (Ormel et al., 2019, 2022). Some interpreters have noted that mental illness is becoming less stigmatized, increasing the willingness to report mental health complaints among patients, and improving clinicians' sensitivity in routine care (Busfield, 2012; Baxter et al., 2014). More critically, others argue that the expansion of “therapy culture” (Baxter et al., 2014) and mental health awareness may lead some individuals to overinterpret milder forms of distress as signs of mental illness, which ultimately amplifies their own symptomatology.
The “prevalence inflation hypothesis” conjectures that destigmatization efforts could have a paradoxical effect on the reported prevalence of mental health problems; but empirical confirmation of this theory is still lacking (Foulkes & Andrews, 2023).
It is also important to note that, despite gradual improvements, the treatment gap among individuals who suffer from mental disorders is still enormous: even in high-income countries, less than half are currently receiving minimally adequate care (Alonso et al., 2018; Evans-Lacko et al., 2018; Thornicroft et al., 2017); and treatment rates are even lower in low and middle-income countries (Ndetei et al., 2023).
Infrastructural barriers are often named as a reason for this unmet need for treatment. In many low and middle-income countries, for example, there is less than one mental health professional per 100'000 individuals (Rathod et al., 2017). However, this cannot account for the low uptake rates observed even when mental health interventions are freely available to entire populations, as is the case in high-income countries (Cuijpers et al., 2010). Attitudinal barriers are therefore increasingly studied as an important contributor to the global treatment gap, including patients' preference to self-manage their own symptoms (Andrade et al., 2014; Ebert et al., 2019).
Another problem is that even the best-studied treatments only show modest benefits (Cuijpers, Miguel, Ciharova, et al., 2023; Kamp et al., 2024; Khan et al., 2021). It has been estimated that, even under 100% coverage with evidence-based treatment, only 28% of the disease burden of mental illness could actually be avoided (Andrews et al., 2004).
Over the last two decades, the prevention of mental disorders has therefore become a relevant research field, especially for depressive disorders (Cuijpers et al., 2012). Meta-analytic evidence shows that psychological interventions can reduce the incidence of major depression within a clearly circumscribed time frame, but their long-term benefits are less certain (Cuijpers et al., 2021; Rigabert et al., 2020).
Thus, the current state of global mental health care gives a mixed picture. The relevance of expanding evidence-based mental health care on a global scale is now almost universally recognized, and clinical research is proliferating at unprecedented speeds (Chen et al., 2023; Liu et al., 2024; López-Muñoz et al., 2003; Wang et al., 2024; Zale et al., 2021); on the other hand, there seems to be no discernable impact of such efforts on the proportion of people living with a mental disorder, the global disease burden, or the effectiveness of treatments received in routine care (Ormel et al., 2020; Ormel & Emmelkamp, 2023).
A recent meta-analysis on the response rates of psychological treatment across eight mental disorders illustrates this issue: for each indication, pooled response rates among the treated were well below 50%; yet, for most disorders, patients are still at least twice as likely to respond under treatment than control (Cuijpers, Miguel, Ciharova, Harrer, et al., 2023; see Figure 1).
This transports a nuanced message: on the one hand, treatments do not lead to meaningful change among the majority of patients. On the other hand, receiving a psychological intervention still strongly increases a patients' chances of improving, indicating that their widespread adoption is all but imperative.
Questions regarding the benefits of psychological treatment are not a new phenomenon. Debates concerning if, how, when and why psychotherapies are effective accompany the field since its inception. The next chapter provides a brief history of psychological treatment research; it traces back main developments within the last 50 years, and discusses unresolved controversies. This historical review builds the basis, in the following chapter, to assess the extent to which psychotherapy research has “progressed” over the last decades.
