What is the incidence of mental illness in adults in the United States?

Incidence of Mental Illness in Adults in the United States

According to the most recent data, approximately 25% of adults in the United States reported having a mental illness in the previous year, representing a substantial public health burden with significant impacts on morbidity, mortality, and quality of life. 1

Overall Prevalence and Classification

Mental health disorders are defined as "medical conditions that affect a person's thoughts, feelings, mood, ability to relate to others, and daily functioning" 2. These conditions involve significant alterations in cognition, emotional regulation, or behavior that result in functional impairment across various domains of life.

The prevalence of mental illness in the US adult population can be broken down as follows:

• General mental illness: Approximately 25% of adults reported having a mental illness in the previous year 1
• Serious mental illness (SMI): An estimated 4.2% of the adult population (approximately 10 million adults) met criteria for SMI in 2013 3
• Depression: 6.8% of adults had moderate to severe depression according to the 2005-2008 National Health and Nutrition Examination Survey 1
• Substance use disorders: 8.2% of the population aged 12 years or older (21.6 million persons) were classified with substance dependence or abuse in 2013 3
• Co-occurring disorders: 3.2% of adults (7.7 million persons) had co-occurring substance use and mental health disorders 3

Serious Mental Illness

Serious mental illness (SMI) deserves special attention due to its significant impact on functioning and mortality:

• SMI is defined as a "diagnosable mental, behavioral, or emotional disorder that results in serious functional impairment, substantially interfering with major life activities" 3
• Common diagnoses associated with SMI include schizophrenia, major depression, and bipolar disorder 3
• People with SMI experience:
  • Shortened life spans
  • Higher rates of substance abuse
  • More physical comorbidities
  • Increased rates of homelessness and unemployment 3
  • Higher likelihood of incarceration (35% of adults with SMI reported a history of homelessness or jail time) 4

Substance Use Disorders

Substance use disorders represent a significant component of mental health burden:

• Overall substance dependence/abuse: 8.2% of population aged 12+ years 3
• Alcohol dependence/abuse: 17.3 million people 3
• Illicit drug dependence/abuse: 6.9 million people 3
• Both alcohol and illicit drugs: 2.6 million people 3

Marijuana remains the most commonly abused substance after alcohol, followed by pain relievers and cocaine 3.

Geographic and Demographic Variations

Mental illness prevalence shows important geographic and demographic patterns:

• Depression rates are generally higher in southeastern states compared to other regions 1
• Adult women are more likely to be diagnosed with mental illness than men 3
• Social disadvantage correlates strongly with serious mental illness 4
• Young adults and African Americans are less likely to receive adequate treatment for serious mental illness 5

Treatment Gaps

Despite the high prevalence, significant treatment gaps exist:

• Only 40% of individuals with serious mental illness received treatment in a 12-month period 5
• Of those receiving treatment, only 38.9% received care that could be considered at least minimally adequate 5
• This results in just 15.3% of all individuals with serious mental illness receiving minimally adequate treatment 5
• Fewer than two-thirds of adults with serious mental illness had seen a mental health professional in the past year 4
• Approximately 5% of ambulatory care visits involved patients with a diagnosis of a mental health disorder, with most classified as depression, psychoses, or anxiety disorders 1

Economic Impact

The economic burden of mental illness in the United States is substantial:

• Approximately $300 billion in 2002 1
• Mental illnesses account for a larger proportion of disability in developed countries than any other group of illnesses, including cancer and heart disease 1

Clinical Implications

Understanding the high prevalence of mental illness has important implications for healthcare providers:

• Routine screening for common mental health conditions should be implemented in primary care settings
• Particular attention should be paid to high-risk populations, including those with social disadvantage
• Integration of mental health services into primary care may help address treatment gaps
• Providers should be aware of the high rates of comorbidity between mental illness and substance use disorders

Mental health surveillance should be expanded to include a wider range of psychiatric conditions, with particular attention to anxiety disorders and changes in depression prevalence at national, state, and county levels 1.