The five most common mental disorders in the United States are anxiety disorders, major depression, ADHD, post-traumatic stress disorder (PTSD), and substance use disorders. Together, these conditions affect tens of millions of Americans each year, and rates have climbed since 2019. In 2024, roughly 62 million U.S. adults had a mental illness, and nearly half of them received no treatment.
Here’s what each of these conditions looks like, how widespread it is, and what sets it apart from the others.
Anxiety Disorders
Anxiety disorders are the single most common category of mental illness. They include several distinct conditions: specific phobias (affecting 8% to 12% of U.S. adults in a given year), social anxiety disorder (7%), generalized anxiety disorder (about 3% of adults), and panic disorder (2% to 3%). A person can have more than one type at the same time, which is common.
What unifies these conditions is persistent, disproportionate fear or worry that interferes with daily life. Generalized anxiety disorder, for example, involves ongoing worry about everyday things like job responsibilities, family health, or minor tasks. That worry comes with physical symptoms: muscle tension, restlessness, fatigue, trouble sleeping, and difficulty concentrating. Unlike ordinary stress, it doesn’t resolve when the stressful situation passes.
Social anxiety disorder centers on a fear of being judged or embarrassed in social situations, often intense enough to make people avoid work meetings, parties, or even phone calls. Panic disorder involves sudden episodes of overwhelming fear with physical symptoms like chest tightness and a racing heart, sometimes mistaken for a heart attack. These episodes can strike without warning, and the fear of having another one can become its own source of anxiety.
Most anxiety disorders begin early in life. Social phobia typically starts in childhood or adolescence, and generalized anxiety disorder can develop anytime between childhood and middle age, though risk is highest in that window. Between 2019 and 2022, the percentage of U.S. adults reporting anxiety symptoms rose from 15.6% to 18.2%, a trend seen across age groups, racial groups, income levels, and geographic regions.
Major Depression
An estimated 21 million U.S. adults, or 8.3% of the adult population, had at least one major depressive episode in 2021. Among adolescents aged 12 to 17, the rate was even higher: 5 million, representing about 20% of that age group.
A major depressive episode is defined as at least two weeks of depressed mood or loss of interest in activities you normally enjoy, combined with a cluster of other symptoms: changes in sleep, appetite, or energy levels, difficulty concentrating, feelings of worthlessness, or thoughts of death. The average age of onset is the mid-20s, though depression can develop at any age. For many people, episodes recur throughout life.
Depression is more than sadness. It affects the ability to work, maintain relationships, and handle basic tasks. The CDC found that the percentage of adults reporting depressive symptoms increased from 18.5% in 2019 to 21.4% in 2022. That means roughly one in five adults experienced some level of depression in a two-week period. These increases showed up across nearly every demographic group studied, suggesting broad societal factors at play rather than changes limited to any single population.
ADHD
Attention-deficit/hyperactivity disorder is one of the most common neurodevelopmental conditions, diagnosed in about 7 million U.S. children aged 3 to 17, or 11.4% of that age group, based on 2022 survey data. That number grew by roughly 1 million children compared to 2016. While ADHD has historically been thought of as a childhood condition, it frequently persists into adulthood, and adult diagnosis rates have risen sharply in recent years.
ADHD involves persistent patterns of inattention, hyperactivity, impulsivity, or some combination of the three. In children, this often shows up as difficulty staying on task in school, fidgeting, and acting without thinking through consequences. In adults, it tends to look different: chronic procrastination, trouble managing time, difficulty following through on projects, and restlessness that’s more internal than physical. Many adults aren’t diagnosed until their 20s or 30s, sometimes after their own child receives a diagnosis.
State-level estimates vary widely, from 6% to 16% of children, reflecting differences in screening practices and access to care as much as differences in actual prevalence.
Post-Traumatic Stress Disorder
PTSD has a lifetime prevalence of about 6.8% in the U.S., meaning roughly 1 in 15 people will experience it at some point. It develops after exposure to a traumatic event such as combat, sexual assault, a serious accident, or a natural disaster. Not everyone who experiences trauma develops PTSD, but for those who do, symptoms can last months or years without treatment.
The hallmark symptoms fall into four clusters: intrusive memories or flashbacks of the event, avoidance of anything that triggers reminders, negative changes in mood and thinking (like persistent guilt, emotional numbness, or loss of interest), and heightened reactivity such as being easily startled, having angry outbursts, or struggling to sleep. These symptoms need to persist for more than a month and significantly disrupt daily functioning to meet the diagnostic threshold.
PTSD was once classified as an anxiety disorder, but it now has its own category in diagnostic manuals: trauma- and stressor-related disorders. This distinction matters because while anxiety disorders involve fear or worry that may have no clear trigger, PTSD is specifically tied to one or more traumatic experiences. Treatment approaches differ accordingly, often involving therapies designed to help the brain process and recontextualize traumatic memories.
Substance Use Disorders
Substance use disorders round out the top five, affecting millions of Americans who develop a pattern of alcohol or drug use that causes significant impairment or distress. This includes alcohol use disorder, opioid use disorder, and disorders involving stimulants, cannabis, or other substances. The condition ranges from mild to severe, based on how many diagnostic criteria a person meets.
What separates a substance use disorder from heavy use is the loss of control: continued use despite clear negative consequences, inability to cut back despite wanting to, spending increasing amounts of time obtaining or recovering from the substance, and developing tolerance or withdrawal symptoms. These disorders frequently co-occur with other conditions on this list. Someone with untreated anxiety or depression, for instance, may turn to alcohol or drugs to manage symptoms, which can develop into its own disorder over time.
Overlap Between Conditions
These five conditions rarely exist in isolation. Anxiety and depression co-occur so frequently that clinicians often screen for both whenever one is present. ADHD in adults frequently comes alongside anxiety, depression, or substance use problems. PTSD commonly overlaps with depression, substance use disorders, or both.
This overlap can complicate both diagnosis and treatment. Someone experiencing fatigue, poor concentration, and irritability could be dealing with depression, generalized anxiety, ADHD, or a combination. Symptoms that don’t improve with treatment for one condition sometimes turn out to be driven by an unrecognized second condition.
The Treatment Gap
Despite how common these disorders are, a large portion of people who have them never receive professional help. In 2024, about 48% of U.S. adults with a mental illness did not receive treatment. That’s nearly 30 million people. Barriers include cost, lack of available providers (especially in rural areas), stigma, and difficulty recognizing symptoms as something treatable rather than a personal failing.
The increases in anxiety and depression since 2019 have been broad, affecting people across all income levels, education backgrounds, racial groups, and regions of the country. This pattern suggests the treatment gap isn’t simply a problem of access in underserved communities. It’s a structural issue affecting the mental health system as a whole.