Risk factors

The predominant view as of 2018 is that genetic, psychological, and environmental factors all contribute to the development or progression of mental disorders. Different risk factors may be present at different ages, with risk occurring as early as during prenatal period.

Genetics

A number of psychiatric disorders are linked to a family history (including depression, narcissistic personality disorder and anxiety). Twin studies have also revealed a very high heritability for many mental disorders (especially autism and schizophrenia). Although researchers have been looking for decades for clear linkages between genetics and mental disorders, that work has not yielded specific genetic biomarkers yet that might lead to better diagnosis and better treatments.

Statistical research looking at eleven disorders found widespread assortative mating between people with mental illness. That means that individuals with one of these disorders were two to three times more likely than the general population to have a partner with a mental disorder. Sometimes people seemed to have preferred partners with the same mental illness. Thus, people with schizophrenia or ADHD are seven times more likely to have affected partners with the same disorder. This is even more pronounced for people with autism spectrum disorders who are 10 times more likely to have a spouse with the same disorder.

Environment

During the prenatal stage, factors like unwanted pregnancy, lack of adaptation to pregnancy or substance abuse during pregnancy increases the risk of developing a mental disorder. Maternal stress and birth complications including prematurity and infections have also been implicated in increasing susceptibility for mental illness. Infants neglected or not provided optimal nutrition have a higher risk of developing cognitive impairment.

Social influences have also been found to be important, including abuse, neglect, bullying, social stress, traumatic events, and other negative or overwhelming life experiences. Aspects of the wider community have also been implicated, including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures. The specific risks and pathways to particular disorders are less clear, however.

Nutrition also plays a role in mental disorders.

In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, abuse of drugs, and urbanicity.

In anxiety, risk factors may include parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behaviour, and child abuse (emotional, physical and sexual). Adults with imbalance work to life are at higher risk for developing anxiety.

For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness.

Drug use

Mental disorders are associated with drug use including: cannabis, alcohol and caffeine, use of which appears to promote anxiety. For psychosis and schizophrenia, usage of a number of drugs has been associated with development of the disorder, including cannabis, cocaine, and amphetamines. There has been debate regarding the relationship between usage of cannabis and bipolar disorder. Cannabis has also been associated with depression. Adolescents are at increased risk for tobacco, alcohol and drug use; Peer pressure is the main reason why adolescents start using substances. At this age, the use of substances could be detrimental to the development of the brain and place them at higher risk of developing a mental disorder.

Chronic disease

People living with chronic conditions like HIV and diabetes are at higher risk for developing a mental disorder. People living with diabetes experience significant stress from biological impact of the disease, which places them at risk for developing anxiety and depression. Diabetic patients also have to deal with emotional stress trying to manage the disease. Conditions like heart disease, stroke, respiratory conditions, cancer and arthritis increase the risk of developing a mental disorder when compared to the general population.

Personality traits

Risk factors for mental illness include a propensity for high neuroticism or "emotional instability". In anxiety, risk factors may include temperament and attitudes (e.g. pessimism).

Causal Models

Mental disorders can arise from multiple sources, and in many cases there is no single accepted or consistent cause currently established. An eclectic or pluralistic mix of models may be used to explain particular disorders. The primary paradigm of contemporary mainstream Western psychiatry is said to be the biopsychosocial model which incorporates biological, psychological and social factors, although this may not always be applied in practice.

Biological psychiatry follows a biomedical model where many mental disorders are conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience. A common assumption is that disorders may have resulted from genetic and developmental vulnerabilities, exposed by stress in life (for example in a diathesis–stress model), although there are various views on what causes differences between individuals. Some types of mental disorders may be viewed as primarily neurodevelopmental disorders.

Evolutionary psychology may be used as an overall explanatory theory, while attachment theory is another kind of evolutionary-psychological approach sometimes applied in the context of mental disorders. Psychoanalytic theories have continued to evolve alongside and cognitive-behavioral and systemic-family approaches. A distinction is sometimes made between a "medical model" or a "social model" of disorder and disability.