Home / Health / Articles / How common is mental illness?

In 2019, adults in the US experienced mental illness at a higher rate than the decade prior. Within the previous year, 20.6% of adults had experienced a mental illness,[1] compared to 18.1% in 2009, according to estimates from the Substance Abuse and Mental Health Services Administration.[2]

The increase is more pronounced for adults ages 18–25, reflecting trends among children and teens in recent years. The implications reach throughout the world of public policy, prompting discussions about mental health and access to professional services, alternatives to police responses to mental health crises, and the role of schools in addressing mental health at an early age.

Embed on your website

How do public health officials define mental illness?

According to the National Institute of Mental Health, a mental illness is any mental, behavioral, or emotional disorder. Mental illnesses can affect an individual’s thinking, mood, and behavior, and range from causing mild effects to substantially interfering with daily life.

Serious mental illness is a subset of mental illness that results in “serious functional impairment” and disability. Examples include bipolar disorder, major depressive disorder, and schizophrenia.

How many people in the US have a mental illness?

Mental illness is a common health condition, affecting more than one in five adults in the US in 2021, according to the Substance Abuse and Mental Health Services Administration (SAMHSA). More than one in five teens have had a “seriously debilitating” mental illness at some point in their lives, and more than one in 20 adults lives with a serious mental illness.

SAMHSA reports that suicide is a leading cause of death in the US — twice as common as homicide, and the second most common cause of death for Americans between 10 and 24 years old.

Mental illness by age, over time

Mental illness rates have increased in recent decades, according to data from SAMHSA. In 2009, about 18.1% of US adults were estimated to have had a mental illness within the previous year. In 2019, that had risen to 20.6%.[3]

Adults between 18 and 25 years old have had the largest increase in rates of mental illness, from 18% in 2009 to 29.4% in 2019. Mental health among children and teens has become a growing concern in recent years, with the CDC declaring teen mental health is in crisis.

Embed on your website

Serious mental illness by age group, over time

In 2021, 5.5% of adults experienced a serious mental illness within that past year. Rates of serious mental illness have increased most significantly in younger adults between the ages of 18–25, with rates increasing from 3.3% in 2009 to 8.6% in 2019.

The US Surgeon General’s Office found that rates of anxiety and depression rose among children and teens before the pandemic, which was attributed to the growing prominence of digital media and greater academic pressure, as well as limited access to mental health care.

Mental illness by gender, over time

Women consistently experience mental illness at higher rates than men, according to SAMHSA data. In 2021, more than one in four women (27.2%) had experienced a mental illness, compared to less than one in six men (18.1%).

Embed on your website

Serious mental illness by gender, over time

Serious mental illness is more common among women (7% in 2021) than men (4%), though rates have increased among both groups since a decade ago.

Mental illness by region, over time

Mental illnesses are more common in the West and Midwest, where in 2021, about 24.2% and 23.1% of adults were estimated to have had a mental illness within the past year.

Serious mental illness diagnoses by region, over time

Serious mental illness among adults has become more prevalent in each region since 2008. The Northeast has seen the lowest rates and the slowest increase, with a prevalence of 4.6% in 2021, compared to 6.1% in the West. The Northeast also has the fewest shortages of mental health providers, while many Western states have severe personnel shortages.

How does substance use affect mental illness?

The link between mental illness and substance use disorders is complex. The National Centers for Mental Health state that either condition may contribute to the development of the other, but both can develop independently. They also share common risk factors, including genetics, stress, and trauma.

Co-occurring substance use disorder and mental illness

In 2021, about 7.6% of US adults had experienced forms of mental illness and substance use disorder within the past year, according to SAMHSA. Younger adults, aged 18–25, showed the highest prevalence of both conditions (13.5%) compared to all adults (7.6%).

Co-occurrence of mental illness and substance use varies by substance type. More people who had used methamphetamines (68.6%) and cocaine (67.3%) also had a mental illness, compared to those with substance use disorders involving marijuana (52.5%) and alcohol (40.3%).

Embed on your website

If you are struggling with mental health issues, call the SAMHSA National Helpline, 1-800-662-HELP (4357), a free, confidential, 24/7, year-round treatment referral and information service. Or, call the 988 Suicide and Crisis Lifeline. If you are thinking about harming yourself or attempting suicide, tell someone who can help immediately and call 911.

Learn more about the role that schools play in addressing youth mental health, the mental health of queer teens, and get the data directly in your inbox by signing up for our email newsletter.


These mental illness estimates are based on a predictive model and are not direct measures of diagnostic status.


Survey methodology changed in 2020 and 2021. Data from these years should be compared to other years with caution.


SAMHSA changed its methodology in 2021, and it doesn't report data from that year alongside historical data.