According to psychologists and psychiatrists, psychological disorders are marked by a clinically significant disturbance in an individual’s cognition, emotion regulation, or behavior. Such dysfunctional or maladaptive thoughts, emotions, or behaviors interfere with daily life, and thus are disordered.

A child (or, less commonly, an adult) who displays extreme inattention and/or hyperactivity and impulsivity may be diagnosed with attention-deficit/hyperactivity disorder (ADHD) and treated with medication and other therapy.

The controversy centers on whether the growing number of ADHD cases reflects overdiagnosis or increased awareness of the disorder, and on the long-term effects of stimulant-drug treatment.

The medical model assumes that psychological disorders are mental illnesses with physical causes that can be diagnosed, treated, and, in most cases, cured through therapy, sometimes in a hospital.

The biopsychosocial approach assumes that disordered behavior comes from the interaction of biological characteristics (genes and physiology), psychological dynamics, and social-cultural circumstances.

Epigenetics also informs our understanding of disorders.

The American Psychiatric Association’s DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition) lists and describes psychological disorders. Diagnostic labels provide a common language and shared concepts for communication and research.

Some critics believe the DSM editions have become too detailed and extensive. Labels can create preconceptions that cause us to view a person differently, and then look for evidence to confirm that view.

It’s common to feel uneasy; when those feelings are intense and persistent they may be classified as disordered.

Anxiety disorders are psychological disorders characterized by distressing, persistent anxiety or maladaptive behaviors that reduce anxiety.

Two other disorders, obsessive-compulsive disorder and posttraumatic stress disorder, involve anxiety (but are classified separately from the anxiety disorders).

Persistent and repetitive thoughts (obsessions), actions (compulsions), or both mark obsessive-compulsive disorder (OCD).

Symptoms of posttraumatic stress disorder (PTSD) include four or more weeks of haunting memories, nightmares, social withdrawal, jumpy anxiety, numbness of feeling, and/or sleep problems following a traumatic event.

The learning perspective views anxiety disorders as a product of fear conditioning, stimulus generalization, fearful-behavior reinforcement, and observational learning of others’ fears and cognitions (interpretations, irrational beliefs, and hypervigilance).

The biological perspective considers genetic predispositions and the role that fears of life-threatening animals, objects, or situations played in natural selection and evolution.

Those with a substance use disorder experience continued substance craving and use despite significant life disruption and/or physical risk.

Psychoactive drugs are any chemical substances that alter perceptions and moods. They may produce tolerance—requiring larger doses to achieve the desired effect—and withdrawal—significant discomfort, due to strong addictive cravings, accompanying attempts to quit.

Depressants (alcohol, barbiturates, opiates) dampen neural activity and slow body functions.

Alcohol disinhibits, increasing the likelihood that we will act on our impulses, whether helpful or harmful. User expectations strongly influence alcohol’s behavioral effects.

Alcohol slows neural processing, disrupts memory, and shrinks the brain in those with alcohol use disorder (marked by tolerance, withdrawal if use is suspended, and a drive to continue problematic use).

Stimulants (caffeine, nicotine, cocaine, amphetamines, methamphetamine, Ecstasy) excite neural activity, speed up body functions, and lead to heightened energy and mood. All are highly addictive.

Nicotine’s effects make the use of tobacco products a difficult habit to kick, yet repeated attempts to quit seem to pay off.

Cocaine gives users a fast high, followed shortly by a crash. Its risks include cardiovascular stress and suspiciousness.

Methamphetamine use may permanently reduce dopamine levels.

Ecstasy (MDMA), which is also a mild hallucinogen, may damage serotonin-producing neurons and impair physical and cognitive functions.

Hallucinogens (LSD, marijuana) distort perceptions and evoke hallucinations (sensory images in the absence of sensory input), some of which resemble the altered consciousness of near-death experiences.

Marijuana’s main ingredient, THC, may trigger feelings of disinhibition, euphoria, relaxation, relief from pain, and intense sensitivity to colors, sounds, tastes, and smells. It may also increase feelings of depression or anxiety, impair motor coordination and reaction time, disrupt memory formation, and damage lung tissue (when inhaled).

Some people are biologically more vulnerable to drugs.

Psychological factors (such as stress, depression, and hopelessness) and social-cultural influences (peer pressure, cultural values) combine to lead many people to experiment with—and sometimes become addicted to—drugs. Cultural and ethnic groups have differing rates of drug use.

A person with major depressive disorder experiences two or more weeks with five or more symptoms, at least one of which must be either (1) depressed mood or (2) loss of interest or pleasure.

A person with the less common condition of bipolar disorder experiences not only depression but also mania (hyperactive and wildly optimistic, impulsive feelings and behavior).

The biological perspective on major depressive disorder and bipolar disorder focuses on genetic predispositions and on abnormalities in brain function, including those found in neurotransmitter systems.

The social-cognitive perspective views depression as an ongoing cycle of stressful experiences (interpreted through negative beliefs, attributions, and memories) leading to negative moods and actions and fueling new stressful experiences.

People with depression are more at risk for suicide than others are, but health status and economic and social frustration are also contributing factors.

Forewarnings of suicide may include verbal hints, giving away possessions, self-inflicted injuries, or withdrawal and preoccupation with death. People who talk about suicide should be taken seriously.

Nonsuicidal self-injury (NSSI) does not usually lead to suicide but may escalate to suicidal thoughts and acts if untreated. People with NSSI generally do not tolerate stress well and tend to be self-critical, with poor communication and problem-solving skills.

Schizophrenia typically strikes during late adolescence and seems to occur in all cultures. It is a disorder characterized by delusions, hallucinations, disorganized speech, and/or diminished, inappropriate emotional expression.

Delusions are false beliefs; hallucinations are sensory experiences without sensory stimulation.

Schizophrenia symptoms may be positive (the presence of inappropriate behaviors) or negative (the absence of appropriate behaviors).

In chronic (or process) schizophrenia, the disorder develops gradually and recovery is doubtful. In acute (or reactive) schizophrenia, the onset is sudden, in reaction to stress, and the prospects for recovery are brighter.

People with schizophrenia have more receptors for dopamine, which may intensify the positive symptoms such as hallucinations and paranoia.

Brain scans have revealed abnormal activity in the frontal lobes, thalamus, and amygdala. Brain abnormalities associated with schizophrenia include enlarged, fluid-filled cerebral cavities and loss of cerebral cortex. Schizophrenia involves not one isolated brain abnormality but problems with several brain regions and their interconnections.

Low weight or oxygen deprivation at birth, mother’s diabetes, father’s older age, and famine conditions during the mother’s pregnancy are possible contributing factors. Converging lines of evidence suggest that fetal-virus infections contribute to the development of schizophrenia.

Twin and adoption studies indicate that the predisposition to schizophrenia is inherited. Multiple genes probably interact to produce schizophrenia.

No environmental causes invariably produce schizophrenia, but environmental events (such as prenatal viruses or maternal stress) may “turn on” genes for this disorder in those who are predisposed to it.

In those with eating disorders, psychological factors can overwhelm the body’s tendency to maintain a normal weight.

Despite being significantly underweight, people with anorexia nervosa (usually adolescent females) continue to diet and sometimes exercise excessively because they view themselves as fat.

Those with bulimia nervosa (usually women in their late teens and early twenties) secretly binge and then compensate with purging, fasting, or excessive exercise.

Those with binge-eating disorder binge but do not follow with purging, fasting, and exercise.

Cultural pressures, low self-esteem, and negative emotions interact with stressful life experiences and genetics to produce eating disorders.

Dissociative disorders are controversial, rare conditions in which conscious awareness seems to become separated (to dissociate) from previous memories, thoughts, and feelings.

Skeptics note that dissociative identity disorder (formerly known as multiple personality disorder) increased dramatically in the late twentieth century, that it is rarely found outside North America, and that it may reflect role playing by people who are vulnerable to therapists’ suggestions. Others view this disorder as a protective response to traumatic experience.

Personality disorders are inflexible and enduring behavior patterns that impair social functioning.

Antisocial personality disorder is characterized by a lack of conscience and, sometimes, by aggressive and fearless behavior. Genetic predispositions may interact with the environment to produce the altered brain activity associated with this disorder.

Mental disorders seldom lead to violence, but when they do, they raise moral and ethical questions about whether society should hold people with disorders responsible for their violent actions. Most people with disorders are nonviolent and are more likely to be victims than attackers.