Healthy people differ significantly in their overall personality, mood, and behavior. Each person also varies from day to day, depending on the circumstances. However, a sudden, major change in personality and/or behavior, particularly one that is not related to an obvious event (such as taking a drug or losing a loved one), often indicates a problem.
(See also Overview of Mental Illness Overview of Mental Illness Mental health (psychiatric or psychologic) disorders involve disturbances in thinking, emotion, and/or behavior. Small disturbances in these aspects of life are common, but when such disturbances... read more .)
Sudden changes in personality and behavior can be roughly categorized as involving one of the following types of symptoms:
Confusion or delirium
Disorganized speech or behavior
Mood extremes (such as depression or mania)
These categories are not disorders. They are just one way doctors organize different types of abnormal thought, speech, and behavior. These changes in personality and behavior can be caused by physical or mental health problems.
People may have more than one type of change. For example, people with confusion due to a drug interaction sometimes have hallucinations, and people with mood extremes may have delusions.
Confusion and delirium
Confusion and delirium Delirium Delirium is a sudden, fluctuating, and usually reversible disturbance of mental function. It is characterized by an inability to pay attention, disorientation, an inability to think clearly... read more refer to a disturbance of consciousness. That is, people are less aware of their environment and, depending on the cause, may be excessively agitated and belligerent or drowsy and sluggish. Some people alternate between being less alert and being overly alert. Their thinking appears cloudy and slow or inappropriate. They have trouble focusing on simple questions and are slow to respond. Speech may be slurred. Often, people do not know what day it is, and they may not be able to say where they are. Some cannot give their name.
Delirium often results from a serious, newly developed physical problem or a reaction to a drug, especially in older people. People who have delirium need immediate medical attention. If the cause of delirium is identified and corrected quickly, delirium often resolves.
Delusions are fixed false beliefs that people hold despite evidence to the contrary. Some delusions are based on a misinterpretation of actual perceptions and experiences. For example, people may feel persecuted, thinking that a person behind them on the street is following them or that an ordinary accident is purposeful sabotage. Other people think that song lyrics or newspaper articles contain messages that refer specifically to them (called a delusion of reference).
Some beliefs seem more plausible and can be difficult to identify as delusions because they could occur or have occurred in real life. For example, people occasionally are followed by government investigators or have their work sabotaged by coworkers. In such cases, a belief can be identified as a delusion by how strongly people hold the belief despite evidence to the contrary.
Other delusions are easier to identify. For example, in religious or grandiose delusions, people may believe they are Jesus or the president of the country. Some delusions are quite bizarre. For example, people may think that their organs have all been replaced by machine parts or that their head contains a radio that receives messages from the government.
Disorganized speech refers to speech that does not contain the expected logical connections between thoughts or between questions and answers. For example, people may jump from one topic to another without ever finishing a thought. The topics may be slightly related or entirely unrelated. In other cases, people respond to simple questions with long, rambling answers, full of irrelevant detail. Answers may be illogical or completely incoherent. This type of speech differs from the difficulty expressing or understanding language ( aphasia Aphasia Aphasia is partial or complete loss of the ability to express or understand spoken or written language. It results from damage to the areas of the brain that control language. People may have... read more ) or forming words ( dysarthria Dysarthria Dysarthria is loss of the ability to articulate words normally. Speech may be jerky, staccato, breathy, irregular, imprecise, or monotonous, but people can understand language and use it correctly... read more ) that is caused by a brain disorder such as stroke.
Occasionally misspeaking or intentionally being evasive, rude, or humorous is not considered disorganized speech.
Disorganized behavior refers to doing quite unusual things (such as undressing or masturbating in public or shouting and swearing for no apparent reason). People with disorganized behavior typically have trouble doing normal daily activities (such as maintaining good personal hygiene or obtaining food).
Hallucination refers to hearing, seeing, smelling, tasting, or feeling things that are not actually there. That is, people perceive things, seemingly through their senses, that are not caused by an outside stimulus. Any sense can be involved. The most common hallucinations involve hearing things (auditory hallucinations), usually voices. The voices often make derogatory comments about the person or command the person to do something.
Not all hallucinations are caused by a mental disorder. Psychedelic drugs Hallucinogens Hallucinogens are a class of drugs that cause profound distortions in people's perceptions. Hallucinogens distort and intensify sensations, but the actual effects are variable and highly unpredictable... read more , such as LSD, mescaline, and psilocybin, are referred to as hallucinogens because they can cause visual hallucinations. Some types of hallucinations are more likely to be caused by a neurologic disorder Introduction to Symptoms of Brain, Spinal Cord, and Nerve Disorders Disorders that affect the brain, spinal cord, and nerves are called neurologic disorders. Neurologic symptoms—symptoms caused by a disorder that affects part or all of the nervous system—can... read more . For example, before a seizure occurs, people may smell something when there is no smell (an olfactory hallucination).
Mood extremes include outbursts of rage, periods of extreme elation ( mania Mania In bipolar disorder (formerly called manic-depressive illness), episodes of depression alternate with episodes of mania or a less severe form of mania called hypomania. Mania is characterized... read more ) or depression Depression A short discussion of prolonged grief disorder. Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to... read more , and, conversely, constant expression of little or no emotion (appearing unresponsive or apathetic).
Although people sometimes assume that changes in personality, thinking, or behavior are all due to a mental disorder, there are many possible causes. All causes ultimately involve the brain, but dividing them into four categories can be helpful:
Drugs (including drug intoxication, withdrawal, and side effects)
Disorders that affect mainly the brain
Bodywide (systemic) disorders that also affect the brain
Mental disorders include
Dissociative disorders Overview of Dissociative Disorders Occasionally everyone has minor problems integrating their memories, perceptions, identity, and consciousness. For example, people may drive somewhere and then realize that they do not remember... read more (when people feel detached from themselves or from the world around them)
Somatic disorders Overview of Somatic Symptom and Related Disorders Somatic symptom and related disorders are mental health disorders characterized by an intense focus on physical (somatic) symptoms that causes significant distress and/or interferes with daily... read more (when mental factors are expressed as physical symptoms)
Drugs may affect personality or behavior when they cause
Intoxication: Particularly alcohol Alcohol Alcohol (ethanol) is a depressant. Consuming large amounts rapidly or regularly can cause health problems, including organ damage, coma, and death. Genetics and personal characteristics may... read more (when consumed in large amounts), amphetamines Amphetamines Amphetamines are stimulant drugs that are used to treat certain medical conditions, but are also subject to abuse. Amphetamines increase alertness, enhance physical performance, and produce... read more , cocaine Cocaine Cocaine is an addictive stimulant drug made from leaves of the coca plant. Cocaine is a strong stimulant that increases alertness, causes euphoria, and makes people feel powerful. High doses... read more , hallucinogens Hallucinogens Hallucinogens are a class of drugs that cause profound distortions in people's perceptions. Hallucinogens distort and intensify sensations, but the actual effects are variable and highly unpredictable... read more (such as LSD), and phencyclidine Ketamine and Phencyclidine (PCP) Ketamine and phencyclidine are chemically similar drugs used for anesthesia but are sometimes used recreationally. Ketamine is available in powder and liquid form. The powder can be snorted... read more (PCP)
Withdrawal: Alcohol Withdrawal symptoms Alcohol (ethanol) is a depressant. Consuming large amounts rapidly or regularly can cause health problems, including organ damage, coma, and death. Genetics and personal characteristics may... read more , barbiturates Withdrawal symptoms , benzodiazepines Withdrawal symptoms Antianxiety and sedative drugs are prescription drugs used to relieve anxiety and/or help with sleep, but their use can result in dependency and a substance use disorder. Using prescription... read more , and opioids Opioids Opioids are a class of drugs derived from the opium poppy (including synthetic variations) that are pain relievers with a high potential for misuse. Opioids are used to relieve pain, but they... read more
Side effects Drug Effectiveness and Safety The main goals of drug development are demonstrating the effectiveness and safety of the drug. Because all drugs can harm as well as help, safety is relative. The difference between the usual... read more : Drugs intended to affect brain function (including antiseizure drugs Antiseizure drugs In seizure disorders, the brain's electrical activity is periodically disturbed, resulting in some degree of temporary brain dysfunction. Many people have unusual sensations just before a seizure... read more , antidepressants Drug Treatment for Depression Agomelatine, a new type of antidepressant, is a possible treatment for major depressive episodes. Several types of drugs can be used to treat depression: Selective serotonin reuptake inhibitors... read more , antipsychotics Antipsychotic drugs Schizophrenia is a mental disorder characterized by loss of contact with reality (psychosis), hallucinations (usually, hearing voices), firmly held false beliefs (delusions), abnormal thinking... read more , sedatives Antianxiety and Sedative Drugs Antianxiety and sedative drugs are prescription drugs used to relieve anxiety and/or help with sleep, but their use can result in dependency and a substance use disorder. Using prescription... read more , and stimulants), drugs with anticholinergic effects Anticholinergic: What Does It Mean? (such as antihistamines), opioid pain relievers Opioid Pain Relievers Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more , and corticosteroids Corticosteroids Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more
Rarely, certain antibiotics and drugs used to treat high blood pressure cause changes in personality and behavior.
Disorders that mainly affect the brain
These disorders can affect personality, mood, and behavior. They include
Brain infections, such as meningitis Introduction to Meningitis Meningitis is inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid space). Meningitis can be... read more , encephalitis Encephalitis Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved... read more , and human immunodeficiency virus (HIV) infection that involves the brain (called HIV-associated encephalopathy HIV-Associated Dementia HIV-associated dementia is progressive deterioration in mental function due to infection of the brain with human immunodeficiency virus (HIV). Unlike almost all other forms of dementia, HIV-associated... read more )
Bodywide disorders that also affect the brain
Bodywide disorders that also affect the brain include
Thyroid disorders, such as an underactive thyroid gland ( hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more ) or an overactive thyroid gland ( hyperthyroidism Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more )
Less commonly, Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by Borrelia species, primarily by Borrelia burgdorferi and sometimes by Borrelia mayonii in the United States. These... read more , sarcoidosis Sarcoidosis Sarcoidosis is a disease in which abnormal collections of inflammatory cells (granulomas) form in many organs of the body. Sarcoidosis usually develops in people aged 20 to 40, most often people... read more , syphilis Syphilis Syphilis is a sexually transmitted infection caused by the bacteria Treponema pallidum. Syphilis can occur in three stages of symptoms, separated by periods of apparent good health. It... read more , or a vitamin deficiency causes personality and behavior changes.
During the initial evaluation, doctors try to determine whether symptoms are due to a mental or physical disorder.
The following information can help people decide when a doctor’s evaluation is needed and help them know what to expect during the evaluation.
In people with changes in personality or behavior, certain symptoms and characteristics are cause for concern. These warning signs include
Symptoms that appear suddenly
Attempts to harm themselves or others or threats to do so
Confusion or delirium
Symptoms that suggest malfunction of the brain, such as difficulty walking, balancing, or speaking or vision problems
A recent head injury (within several weeks)
When to see a doctor
People who have warning signs should be seen by a health care practitioner as soon as possible. Law enforcement may need to be called if people are violent.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination, including a neurologic examination Neurologic Examination When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more with a mental status examination Mental Status When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more (which evaluates the ability to pay attention, memory, mood, and ability to think abstractly, follow commands, and use language, among other things). What they find during the history and physical examination often suggests a possible cause of the changes and the tests that may need to be done (see table Some Causes and Features of Personality and Behavior Changes Some Causes and Features of Personality and Behavior Changes ).
Questions include when symptoms began. Many mental disorders begin in a person's teens or 20s. If a mental disorder begins during middle age or later, especially if there is no obvious trigger (such as loss of a loved one), the cause is more likely to be a physical disorder. A physical disorder is also more likely to be the cause when mental symptoms change significantly during middle age or later in people with a chronic mental disorder. If changes began recently and suddenly in people of any age, doctors ask about conditions that can trigger such changes. For example, they ask whether people have just started or stopped taking a prescription or recreational drug.
Doctors ask about other symptoms that may suggest a cause, such as
Palpitations: Possibly an overactive thyroid gland or use or withdrawal of a drug
Tremors: Parkinson disease or withdrawal of a drug
Difficulty walking or speaking: Multiple sclerosis, Parkinson disease, stroke, or intoxication from an opioid or a sedative
Headache: Brain infection, brain tumor, or bleeding in the brain (hemorrhage)
Numbness or tingling: A stroke, multiple sclerosis, or a vitamin deficiency
People are also asked whether they have previously been diagnosed and treated for a mental or seizure disorder. If they have been treated, doctors ask whether they have stopped taking their drugs or decreased the dose. However, because people with mental disorders may also develop physical disorders, doctors do not automatically assume that any new abnormal behavior is caused by the mental disorder.
Doctors ask about physical disorders people have (such as diabetes) and about their lifestyle (such as their marital status, job situation, educational background, use of alcohol, tobacco, and recreational drugs, and living arrangements). Doctors also ask whether family members have had any physical disorders that can cause mental symptoms (such as multiple sclerosis).
During the physical examination, doctors look for signs of physical disorders that can cause changes in mental status, particularly the following:
Fever and/or a rapid heart rate (suggesting an infection, alcohol withdrawal, or use of amphetamines or cocaine in high doses)
Confusion or delirium (suggesting drug intoxication or withdrawal)
Abnormalities during the neurologic examination, such as difficulty forming words or understanding language (possibly suggesting a brain disorder)
Confusion and delirium are more likely to result from a physical disorder. People with mental disorders are rarely confused or delirious. However, many physical disorders that cause changes in behavior do not cause confusion or delirium, but they often cause other symptoms that may appear to be a mental disorder.
Doctors bend the person's neck forward. If doing so is difficult or painful, meningitis may be the cause. Doctors check the legs and abdomen for swelling, which may result from kidney or liver failure. If the skin or whites of the eyes look yellow, the cause may be liver failure.
Doctors may examine the interior of the eyes with a handheld device that looks like a small flashlight (called an ophthalmoscope Ophthalmoscopy A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more ). If doctors see swelling in part of the optic nerve ( papilledema Papilledema Papilledema is a condition in which increased pressure in or around the brain causes the part of the optic nerve inside the eye to swell. Symptoms may be fleeting disturbances in vision, headache... read more ), pressure within the skull may be increased, and tumors or bleeding in the brain may be the cause of the mental symptoms.
Typically, tests include the following:
Measurement of the oxygen level in the blood using a sensor clipped to the person's fingertip (called pulse oximetry)
Blood tests to measure sugar (glucose) levels
Blood tests to measure levels of alcohol and levels of any antiseizure drugs Antiseizure drugs In seizure disorders, the brain's electrical activity is periodically disturbed, resulting in some degree of temporary brain dysfunction. Many people have unusual sensations just before a seizure... read more the person is taking
Urine tests to check for drugs
A complete blood count (CBC)
Sometimes blood tests to measure electrolyte levels and to evaluate kidney function
For most people known to have a mental disorder, no further testing is needed if their only symptoms are worsening of their typical symptoms, if they are awake and alert, and if results of these tests and their physical examination are normal.
For most other people, blood tests to check for HIV infection are usually done.
Other tests are done based mainly on the symptoms and examination results (see table Some Causes and Features of Personality and Behavior Changes Some Causes and Features of Personality and Behavior Changes ). Tests may include
Computed tomography Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more (CT) or magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more (MRI) of the brain: If symptoms of mental dysfunction have just appeared or if people have delirium, a headache, a recent head injury, or any abnormality detected during the neurologic examination
A spinal tap Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more (lumbar puncture): If people have symptoms of meningitis or if results of CT are normal in people with a fever, a headache, or delirium
Blood tests to evaluate thyroid function: If people are taking lithium, have symptoms of a thyroid disorder, or are over 40 years old and have personality or behavior changes that have just started (particularly people with a family history of thyroid disorders and women)
Chest x-ray: If people have a fever or a productive cough or they cough up blood
Blood cultures (to check for bacteria in the bloodstream): If people are very ill and have a fever
Blood tests to evaluate liver function: If people have symptoms of a liver disorder, such as jaundice (a yellowish discoloration of the skin and whites of the eyes), or a history of alcohol or drug use disorder, or if specific information about them is not available
The underlying condition is corrected or treated when possible. Whatever the cause, people who are a danger to themselves or others typically need to be hospitalized and treated whether they are willing or not. Many states require that such decisions be made by someone appointed to make health care decisions for the mentally ill person (called a surrogate decision maker Default Surrogate Decision Making If a person is unable to make decisions about personal health care, some other person or people must provide direction in decision making. The general term for such person is surrogate decision... read more ). If the person has not appointed a decision maker, doctors may contact the next of kin, or a court may appoint an emergency guardian.
People who are not dangerous to themselves or others can refuse evaluation and treatment, despite the difficulties their refusal may create for themselves and their family.
Not all changes in personality and behavior are due to mental disorders.
Other causes include drugs (including withdrawal and side effects), disorders that mainly affect the brain, and bodywide disorders that affect the brain.
Doctors are particularly concerned about people with symptoms that suggest brain malfunction, such confusion or delirium, fever, headache, people with a recent head injury and people who want to harm themselves or others.
Typically, doctors do blood tests to measure the levels of oxygen, sugar (glucose), and certain drugs (such as antiseizure drugs) the person is taking, and they may do other tests based on the symptoms and results of the examination.