Psychosis is broadly defined as the presence of delusions and hallucinations and can be organic or functional in nature. The former is secondary to an underlying medical condition, such as delirium or dementia, the latter to a psychiatric disorder, such as schizophrenia or bipolar disorder. Functional psychosis is relatively common in the general population, with epidemiological studies estimating its prevalence to be approximately 0.2-0.7%. However, this figure varies depending on a number of factors including the definition used and the age group. By some definitions up to a third of people have experienced psychotic symptoms in their lifetime. Prevalence in the elderly increases to 4.8% and is even higher in nursing home populations. The identification and treatment of psychosis is important as it is associated with a 10% lifetime risk of suicide and significant social exclusion. Delays in recognition can ultimately lead to a worse prognosis.

Depression is common. Depression impairs occupational and social functioning, and has a significant impact on quality of life. Adults in the UK with a diagnosis of either ICD-10 depressive episode or ICD-10 mixed anxiety and depressive disorder have been estimated to have taken more than a quarter (9% and 20% respectively) of the total number of days of sickness absence in one year. Few patients receive effective treatment. There are four reasons for this: failure to seek help (40% don't attend); failure of GPs to recognise depression (30-50% of cases); non-adherence or early cessation of treatment (only about 25% of patients complete a six-month course of antidepressant treatment);lack of treatment efficacy (50% with moderate depression don't respond to initial treatment). Although there is a high rate of spontaneous recovery among those with mild depression, between one- and two-thirds of primary care patients with major depression have not fully recovered 12 months later. The main reason for this is that only about one in ten patients receive effective treatment.

GPs play a crucial role in identifying patients who may be suffering from borderline personality disorder (BPD). All practitioners caring for patients with BPD  should work together in order to understand needs and risks and to provide patients with consistent support and help.BPD is associated with significant impairment of psychological, social and occupational functioning, with a suicide rate of almost 10%, a rate 50 times higher than in the general population.

In bipolar disorder patients are intermittently severely ill and unable to function, but they usually return to their normally functioning self. The extremes of symptoms and experiences require intensive specialist care,  but the overall success of management will depend on an informed and complementary interaction between primary and secondary care. Bipolar disorder is at least twice as common as schizophrenia, and eminently treatable. It is perfectly suited to the well established outpatient model practised in general practice.

Only a small minority of patients receive effective treatment for depression. About 40% of patients do not seek medical help, and of those who do, between 30 and 50% are not recognised as being depressed, usually as a result of somatic presentations. Patients may not be offered the appropriate treatment if strict diagnostic criteria are not applied, and under half of those receiving treatment will complete a minimal treatment course.

In recent decades the care of people with schizophrenia has shifted from hospital to the community. The GP's role has thus expanded, a fact reflected by the emphasis placed on primary care involvement in the recently updated NICE guideline on schizophrenia. On average GPs in the UK will have 7-12 people with schizophrenia on their lists, and for some of these patients they may be the sole provider of care.

Exercise has been suggested as a means to lift mood for many years, and there is increasingly strong evidence for its use as a treatment for depression. Several meta-analyses have produced robust evidence that exercise is effective as a monotherapy for depression. There is also some evidence that exercise is beneficial as an adjunct to pharmacotherapy.

Eating disorders are psychiatric disorders resulting in impaired physical or psychosocial functioning caused by disturbances of eating habits or weight-control behaviour. The diagnosis of eating disorder is only appropriate if the symptoms cannot be attributed to another medical or psychiatric condition

Postnatal depression is known to have a detrimental effect on the mother, baby and the family. Antenatal depression is also important and GPs have a role in managing depression throughout this key period.Women have considerable contact with health professionals before, during and after childbirth. Midwives and GPs are encouraged to use this to identify mental health problems as early as possible in antenatal care and monitor or treat those with symptoms or risk of illness. Infants of mothers with postnatal depression, especially boys, have poorer emotional, behavioural and cognitive development. Infants of women with antenatal anxiety and depression also have altered stress responses, which persist after birth, and are more likely to be born preterm and have a low birth weight. Personal and social relationships can be strained and disrupted, and these women are at a increased risk of domestic violence.

Schizophrenia commonly presents in patients aged 20-30 years, but may present in teenagers. Patients almost always require  intervention to prevent harm and alleviate suffering. Schizophrenia affects one in 100 people in the UK at some time in their lives. Around one in five of these patients will only have one schizophrenic episode. Seven in ten will have two episodes, usually occurring within 5-7 years of each other. The course of illness varies, both in the length of time and quality of recovery between episodes. Even patients  who develop a chronic and disabling course can- in most cases- improve with treatment.