Conventionally, the discipline of psychiatry is often identified with severe mental illnesses like schizophrenia and other psychotic disorders. The movement of psychiatry from inside the walls of the mental hospitals to the community, accompanied by the growth of the general hospital psychiatric units, led to a focus on non-psychotic psychiatric illnesses like depression, anxiety and other neurotic disorders, which also occur more commonly in the community. Goldberg and Huxley (1992), recognising the public health implications and disability associated with these illnesses, introduced the term common mental disorders (CMDs) in the literature. CMDs included anxiety disorders, depression and related neurotic disorders. Though these illnesses exist as separate categories in the classification systems, they often occur as comorbid conditions, and their treatment also tends to be along similar principles. These associations made the term popular, since it was convenient to group these illnesses under this umbrella term. The CMD group would also include somatoform disorders, which commonly present in primary care and general medical settings, and tend to have associated anxiety and depressive symptoms. CMDs are especially important for their public health implications, since these often remain unrecognised in the primary care and medical settings, and are responsible for increased health-care burden and costs (World Health Organisation 2001). Effective treatments exist for the CMDs, and thus, an early diagnosis and management might reduce this huge drain on resources.

This paper discusses epidemiology, nosology, clinical presentation, public health aspects and management of the CMDs with a special focus on the Indian research on the subject.

Epidemiological studies have shown that the CMDs may have an annual prevalence of about 10–12 % with lifetime prevalence going up to 20–25 % (World Health Organisation 2001). Patients with CMDs constitute about 7.3–52.5 % of the clinic populations of primary care settings (Goldberg and Lecrubier 1995). Prevalence of CMDs in primary care settings has varied from about 11–34.6 % in different Indian studies (Nambi et al. 2002). Reasons for this wide variation in prevalence could be due to differences in the inclusion criteria (Nambi et al. 2002). A recent study from India reported a prevalence of 42 % in patients attending a medical outpatient clinic in a tertiary care hospital (Avasthi et al. 2008). About 10 % of the patients presenting in general practice settings have been reported to suffer from depression (Ormel et al. 1993). Prevalence of generalised anxiety disorder in primary care settings is reported to be in range of 5–16 % (Wittchen 2002) and that of panic disorder as 1.5–13 % (Craske et al. 2002).

CMDs are more common in women and in persons belonging to lower socio-economic strata and the marginalised populations (Patel and Kleinman 2003; Patel et al. 2006a).

CMDs can cause significant patient suffering and disability and lead to substantial health-care costs (Smith et al. 1986). Patients with CMDs are more often seen in primary care and general medical settings, rather than in psychiatric services (Manderscheid et al. 1993). Most people with anxiety or depression visit their general practitioner, whether or not they complain of their psychological symptoms (Goldberg and Huxley 1992). Primary care physicians fail to diagnose and treat nearly 50–75 % of patients suffering from CMDs, presenting in their clinical practice (Ormel et al. 1991; Borus et al. 1988).

As is the case with most psychiatric disorders, aetiology of CMDs is multi-factorial, with the socio-economic stressors probably triggering a biological process in vulnerable individuals leading to development of the illness.

Poverty, economic deprivation, low educational status and unemployment have been identified as common risk factors for the development of CMDs (Fryers et al. 2003; Pothen et al. 2003; Shankar et al. 2006). Poverty, being married, tobacco use, history of abnormal vaginal discharge, history of chronic physical illnesses like cardiovascular diseases, diabetes and spinal or back disorders and physical disability are associated with increased risk of developing CMDs in the developing countries (Patel and Kleinman 2003).

Gender disadvantage, exposure to intimate partner violence, sexual and reproductive complaints (e.g., excessive vaginal discharge) and tobacco use have been found to predispose to development of CMDs in women (Prasad et al. 2003; Patel et al. 2006b). Higher prevalence in women is not apparently due to hormonal or other biological mechanisms, but the gender disadvantage especially in form of intimate partner violence and low levels of autonomy in decision making could be the key risk factors for higher prevalence of CMDs in women (Patel et al. 2006b).

Patients with CMDs often present with physical complaints, frequently in primary care settings. Clinical presentation is no different in secondary or tertiary care settings.

The patients commonly present with complaints of subjective weakness, headache, vague somatic sensations, pain in extremities, palpitations, giddiness or dizziness, bodily tremors, numbness or tingling sensations (Chadda et al. 1991; Srinivasan et al. 1986). The Indian patient frequently comes out with a symptom of vague somatic sensations, which is described in words like bharipan (heaviness of parts of the body), halkapan (lightness of the body parts), heat or cold or pin-pricking sensation, houl (restlessness) or gas in body. The person may use different colloquial words to describe the symptoms. An unpleasant sensation may be described as travelling from one body part to other and finally leaving from the head or the feet, defying all anatomical boundaries. Some of the symptoms like difficulty breathing, chest pain, pounding heart or gaseous abdomen are a part of sympathetic overactivity or psychogenic autonomic dysfunction (Chadda 2011).

On screening for psychological symptoms, it is often possible to elicit the specific symptoms of the primary psychiatric illnesses (Chadda 2000, 2010a, b). There may be an admixture of anxiety and depressive symptoms. On the standard classificatory systems, patients with CMDs may receive a diagnosis of depressive episode, generalised anxiety disorder, mixed anxiety depression, panic disorder, undifferentiated somatoform disorder, dysthymia or other anxiety or somatoform disorders (Chadda and Bhatia 1990). Many of them may not fulfil the criteria for a specific disorder and receive a diagnosis of anxiety disorder, unspecified type or depression, unspecified type (Chadda et al. 1991).

Explanatory model interviews have shown that a significant proportion of patients with CMDs, presenting with unexplained physical symptoms in the primary care settings, hold a combination of medical and non-medical views about their condition (Nambi et al. 2002; Shankar et al. 2006). Many of these patients consider that they are having a specific medical disease and attribute their symptoms to a variety of causes. They perceive their illness as serious, and also fear death and major disability. Only a minority of patients presenting in primary care attribute their problems to psychological causes, though many would admit having emotional problems secondary to the physical symptoms (Nambi et al. 2002; Shankar et al. 2006).

Patients, who present with CMDs in psychiatry outpatient settings on being referred from other specialties, may deny having a psychiatric illness. They, however, would accept the treatment offered by the psychiatrist and are also willing to come for follow-up. A belief in somatic model of illness and stigma of being identified as mentally ill could be the reason for the phenomenon.

Recognition of the CMDs is poor in primary care, with less than one-third of clinically significant morbidity detected (Ustun and von Korff 1995). Patients presenting with non-specific somatic symptoms with no apparent physical cause are often prescribed various symptomatic medications, such as vitamins, iron supplements or pain killers, since the primary care physician may not be able to diagnose the underlying CMD. Many such patients are also subjected to unnecessary investigations. A multi-centric study conducted by WHO on mental health problems in general health care reported that nearly 10 % of primary care attendees with CMDs in the Indian study centre were prescribed psychotropic drugs (Linden et al. 1999). The majority of prescriptions were for tranquilisers (benzodiazepines), rather than antidepressant drugs.

In a busy primary care clinic in India and neighbouring countries, the physicians have a very limited time available to screen for CMDs. More so, the primary care physicians have received a limited exposure to psychiatry during their undergraduate training, though some of them might have attended the orientation programmes on mental health conducted under the National Mental Health Programme. Thus, the primary care physicians have an inadequate knowledge of the CMDs and are often unable to reach a correct diagnosis in such patients, since they are not familiar with the appropriate questions to be asked. Undetected psychiatric morbidity in primary care commonly leads to unnecessary investigations, medications and continued suffering of the patient. This inevitably leads to impaired family, occupational and social functioning, thus making it crucial for primary care and general practice physicians to be equipped with the necessary skills and measures for detecting CMDs in their patients and providing the necessary treatment.

In the last two decades, a number of structured screening instruments have been developed for screening the patients presenting with CMDs in primary care settings. Though originally developed for the Western populations, most of these have also been standardised in the Indian population. Some of these are also available in Indian vernacular languages. These include the General Health Questionnaire-12 (GHQ-12) (Gautam et al. 1987; Jacob et al. 1997), the Self-Report Questionnaire (SRQ) (Harding et al. 1980), and the Primary Care Evaluation of Mental Disorders (PRIME-MD)—Patient Health Questionnaire (PHQ) (Avasthi et al. 2008). All of these can be easily administered in 5–10 min. The PRIME-MD-PHQ also provides a psychiatric diagnosis.

Another brief instrument, the Mental Health Inventory (MHI), a 5-item subscale of the Short Form Health Survey (SF-36), can also be used to screen for CMDs in primary care settings. The MHI has 5 basic questions, which can be easily incorporated in clinical assessment. This does not take more than 2–3 min to administer. The five questions are as follows: in the past 4 weeks: (a) Have you been very nervous? (b) Have you felt so down in the dumps that nothing could cheer you up? (c) Have you felt calm and peaceful? (d) Have you felt downhearted and depressed? and (e) Have you been happy? (Fone et al. 2007). The items are rated from 1 to 5. The response scores are converted to scoring on 0–100, where 100 is indicative of best mental health.

Once a patient screens positive on a screening instrument, a formal psychiatric assessment to screen for the specific CMD can be undertaken. This would include screening for depression and anxiety disorders.

CMDs are associated with substantial disease burden and disease-related disability. As per the Global Burden of Disease (GBD) study, mental and neurological disorders were responsible for 10.5 % of the total disability-adjusted life years (DALYs) in 1990 (Murray and Lopez 1996). This was the first time that mental disorders were identified as responsible for a high burden as a result of years lost due to all diseases and injuries. The figure increased to 12.3 % in 2000 (World Health Organisation 2001). Depression has been identified as a fourth leading cause of the DALYs in the 15–44 year age group. In the recently published GBD estimates for the year 2010 (Murray et al. 2012), mental and behavioural disorders were responsible for 7.4 % of all the DALYs. This included major depressive disorder (2.5 %), anxiety disorders (1.1 %), drug use disorders (0.8 %), alcohol use disorders (0.7 %), schizophrenia (0.6 %) and others. In the GBD 2010 report, there was a global shift in the burden of disease from communicable, maternal, neonatal and nutritional disorders to non-communicable diseases and injuries. There was an increase in DALYs from 54,010 to 74,264 (37.6 % increase) due to depression and from 19,664 to 26,826 (36.4 % increase) due to anxiety disorders during the period 1990–2010. On adjusting for the increase in the world population during this period, the increase in DALYs due to depression and anxiety disorders comes out to be 5.8 and 5.0 %, respectively. Mean rank of depression has risen from 15 to 11 in the diseases listed in order of causing DALYs (Murray et al. 2012). Thus, the GBD 2010 report further emphasises the significance of CMDs in relation to disease-related disability and burden associated with this group.

There have also been a number of studies in India which have assessed disability and psychosocial dysfunction due to CMDs. In one of the earliest studies, patients presenting with somatic symptoms with a depressive diagnosis were found to suffer more severe psychosocial dysfunction than those who received a somatoform diagnosis (Chadda et al. 1993). Dysfunction was especially seen in personal, social, familial and vocational functioning and was minimal in cognitive areas. This is understandable, since the CMDs are not expected to affect the higher mental functions. CMDs have been reported to be associated with impaired functioning in family situations, social relations and work performance (Nambi et al. 2002). In the study by Nambi et al., 69 % of the subjects reported their work being affected by the illness, and around 40 % felt that the illness affected their family and social life.