Find information on medical topics, symptoms, drugs, procedures, news and more, written in everyday language.

* This is the Consumer Version. *

Personality and Behavior Changes

by Caroline Carney Doebbeling, MD, MSc

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.

Changes in personality and behavior can be roughly categorized as one of the following:

  • Confusion or delirium

  • Delusions

  • Disorganized speech or behavior

  • Hallucinations

  • Mood extremes (such as depression)

These categories are not disorders. They are just one way doctors organize different types of abnormal thought, speech, and behavior.

People may have more than one type of change. For example, people with confusion due to Alzheimer disease sometimes become depressed, and people with delirium may have disorganized speech or hallucinations.

Confusion and delirium (see Delirium) 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.

Delusions are fixed false beliefs that people hold despite evidence against those beliefs. 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. 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 against it. 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. 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) or to being unable to behave normally. People with disorganized behavior typically have trouble doing normal daily activities (such as maintaining good personal hygiene or obtaining food).

Hallucinations refers to hearing, seeing, smelling, tasting, or feeling things that are not 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. Some types of hallucinations are more likely to be caused by a neurologic disorder. 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) or depression, and, conversely, constant expression of little or no emotion (appearing unresponsive or apathetic).

Causes

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:

  • Mental disorders

  • Drugs (including drug intoxication, withdrawal, and side effects)

  • Disorders that affect mainly the brain

  • Bodywide (systemic) disorders that also affect the brain

Of these causes, drugs are the most common cause overall, followed by mental disorders.

Drugs may affect personality or behavior when they cause

  • Intoxication: Particularly alcohol (when consumed for a long time), amphetamines, cocaine, hallucinogens (such as LSD), and phencyclidine (PCP)

  • Withdrawal: Alcohol, barbiturates, and benzodiazepines

  • Side effects (see Drug Effectiveness and Safety): Drugs intended to affect brain function (including anticonvulsants, antidepressants, antipsychotics, sedatives, and stimulants), drugs with anticholinergic effects (such as antihistamines—see Anticholinergic: What Does It Mean?), opioid pain relievers, and corticosteroids

Rarely, certain antibiotics and drugs used to treat high blood pressure cause changes in personality and behavior.

Mental disorders include

  • Bipolar disorder

  • Depression

  • Schizophrenia

  • Posttraumatic stress disorder

Disorders affecting mainly the brain include

  • Alzheimer disease

  • Brain infections, such as meningitis, encephalitis, and human immunodeficiency virus (HIV) infection that involves the brain (HIV-associated encephalopathy)

  • Brain tumors

  • Head injuries, such as a concussion and postconcussion syndrome (see Concussion)

  • Multiple sclerosis

  • Parkinson disease

  • Seizure disorders

  • Stroke

Bodywide disorders that also affect the brain include

  • Kidney failure

  • Liver failure

  • Low blood sugar (hypoglycemia)

  • Systemic lupus erythematosus (lupus)

  • Thyroid disorders, such as an underactive thyroid gland (hypothyroidism) or an overactive thyroid gland (hyperthyroidism)

Less commonly, Lyme disease, sarcoidosis, syphilis, or a vitamin deficiency causes personality and behavior changes.

Evaluation

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.

Warning signs

In people with changes in personality or behavior, certain symptoms and characteristics are cause for concern. They include

  • Symptoms that appear suddenly

  • Attempts to harm themselves or others or threats to do so

  • Confusion or delirium

  • Fever

  • Headache

  • 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 taken to the hospital right away. Law enforcement may need to be called if people are violent or belligerent.

If people take drugs for diabetes, a fingerstick test to check their blood sugar level should be done if possible. For this test, the finger is pricked to obtain a small sample of blood. If this test cannot be done or if the blood sugar level is low, people should be taken to the hospital right away.

People who have no warning signs should see a doctor within a day or two if the personality or behavior change was recent. If the change occurred gradually over a period of time, people should see a doctor as soon as is practical, but a delay of a week or so is not harmful.

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. What they find during the history and physical examination often suggests a cause of the changes and the tests that may need to be done (see Table: Some Causes and Features of Personality and Behavior Changes).

Doctors ask 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 drug or a recreational (usually illegal) 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.

During the physical examination, doctors look for signs of physical disorders, particularly

  • Fever (suggesting an infection, alcohol withdrawal, or use of amphetamines or cocaine in high doses)

  • A rapid heart rate

  • Confusion or delirium

  • Abnormalities during the neurologic examination

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.

Some Causes and Features of Personality and Behavior Changes

Cause

Common Features*

Tests

Mental disorders

Schizophrenia

Usually symptoms that develop slowly, with mildly disorganized thinking and difficulty coping with daily routines

Later symptoms:

  • Delusions and/or hallucinations

  • Often lack of emotion and disinterest

  • Increasingly disorganized thinking and behavior

  • Difficulty maintaining relationships and employment

A doctor's examination

Bipolar disorder

Symptoms that occur in episodes lasting a few weeks to a few months and that include mania, depression, or both

Episodes of mania:

  • Elation or irritability

  • Grandiosity

  • Talkativeness

  • Racing thoughts, jumping from one idea to another

  • Sometimes hallucinations or delusions of persecution

Episodes of depression:

  • Sluggishness

  • Sadness, despair, and a pessimistic mood

  • Loss of interest in typical pleasures

  • Lack of energy

  • Difficulty sleeping

  • Thoughts of death or suicide

A doctor's examination

Depression

Episodes of depression as described in bipolar disorder (see above) but that last longer

A doctor's examination

Drugs

Use of a drug, particularly

  • Alcohol

  • Amphetamines

  • Cocaine

  • Hallucinogens

  • Phencyclidine (PCP)

Agitation and sometimes panic or aggression

Sometimes hallucinations

With long-term use of alcohol:

  • Sometimes balance problems

  • Twitching eyes

  • An abnormal way of walking

With long-term use of amphetamines:

  • Sometimes paranoia

With short-term excessive use of amphetamines or cocaine:

  • An increased heart rate

  • Sometimes fever

Usually in people known to use the drug

A doctor's examination

Sometimes blood or urine tests to detect the drug

Sometimes EEG

Withdrawal of a drug, particularly

  • Alcohol

  • Barbiturates

  • Benzodiazepines

Typically significant confusion and delirium

Shaking (tremors), headache, sweating, fever, and a rapid heart rate or palpitations

Sometimes seizures, hallucinations, and sleep disturbances

Usually in people known to use the drug

A doctor's examination

Side effects

Vary, depending on the drug

Drugs with anticholinergic effects:

  • Constipation

  • Blurred vision

  • Light-headedness

  • Difficulty starting and stopping urination

  • Dry mouth

Usually in people known to use the drug

A doctor's examination

Sometimes stopping the drug to see whether the symptom goes away

Brain disorders

Alzheimer disease

Symptoms that progress slowly

Loss of short-term memory, difficulty finding the right words, and poor judgment

Difficulty with daily activities (such as balancing a checkbook or finding their way around their neighborhood)

Usually in people over 60

A doctor's examination

Often CT , MRI, or PET of the brain

Detailed testing of mental function involving a series of simple questions and tasks (neuropsychologic testing)

Brain infections such as

  • Encephalitis

  • Herpes simplex encephalitis

  • Meningitis

Headache

Usually confusion and fever

Pain and/or stiffness when the doctor bends the neck forward (more common in people with meningitis)

With herpes simplex encephalitis, hallucinations of bad odors and sometimes seizures

A spinal tap (lumbar puncture)

Often CT or MRI of the brain

Culture of samples of blood, urine, and material from the throat

EEG

Head injuries (such as postconcussion syndrome)

Forgetfulness and headaches

Emotional instability in the weeks after a significant head injury

CT or MRI of the brain

Testing of IQ and executive functions such as the ability to plan and solve problems (neurocognitive testing)

Brain tumors or bleeding (hemorrhage) in the brain

With brain tumors, a headache that develops gradually and is often worse during the night or early morning and when lying flat

With hemorrhage, a headache that starts suddenly (called a thunderclap headache)

Often confusion and drowsiness

Sometimes seizures

CT or MRI of the brain

Multiple sclerosis

Weakness and/or numbness that comes and goes in different parts of the body

Sometimes partial loss of vision or double vision

Sometimes symptoms that are worsened by heat (such as a warm bath or hot weather)

MRI of the brain and spinal cord

Sometimes a spinal tap

Nerve conduction studies (measuring how fast nerves transmit signals) and electromyography (stimulating muscles and recording their electrical activity)

Parkinson disease

Tremors of the hands and fingers while they are at rest

Stiffness and difficulty moving and maintaining balance

Slowed speech and limited facial expressions

A doctor's examination

Seizure disorders (typically complex partial seizures—see Partial seizures)

Episodes of abnormal behavior

Usually confusion and staring

Sometimes involuntary chewing, smacking of the lips, and purposeless movements of the limbs

Typically no loss of consciousness and no general shaking of the body (convulsions)

Sometimes hallucinations of odor or taste

MRI of the brain

EEG

Stroke

Symptoms that appear suddenly

Usually weakness or paralysis on one side of the body and unsteadiness when walking

CT or MRI of the brain

Bodywide (systemic) disorders

Hypoglycemia (a low level of blood sugar)

Weakness, sweating, and confusion

Almost always in people taking drugs for diabetes

Tests to measure the blood sugar (glucose) level

Kidney failure

Swelling of the legs, loss of appetite, and nausea

Weakness that typically develops over several weeks

Blood and urine tests to evaluate how well the kidneys are functioning

Liver failure

Yellow color of the skin and/or whites of the eyes (jaundice)

Usually swelling of legs and/or abdomen

A reddish purple rash of tiny dots (petechiae)

Usually in people already known to have a liver disorder

Blood tests to evaluate how well the liver is functioning (liver function tests)

Systemic lupus erythematosus (lupus)

Usually painful, swollen joints

Often a rash, particularly on the face or areas exposed to sunlight

Sometimes a headache

Blood tests to check for certain antibodies

Thyroid disorders, including

  • Hyperthyroidism (an overactive thyroid gland)

  • Hypothyroidism (an underactive thyroid gland)

Typically in hyperthyroidism: Palpitations, excessive sweating, difficulty tolerating heat, an increased appetite, weight loss, shakiness (tremor), and sometimes bulging eyes

Typically in hypothyroidism: Fatigue, constipation, difficulty tolerating cold, decreased appetite, weight gain, slow speech, sluggishness, a puffy face, drooping eyelids, coarse and thick dry skin, and loss of eyebrow hair

Blood tests to evaluate how well the thyroid gland is functioning

Vitamin deficiency, such as deficiency of thiamin or vitamin B 12

Disorientation, an impaired memory, and irritability

Abnormal sensations in the hands and feet

Other symptoms, depending on which vitamin is deficient

Blood tests to measure vitamin levels

*Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present.

These disorders typically begin in a person's teens to mid-20s. People are usually alert and are not confused or delirious. Results of their physical examination (including the neurologic examination) are normal.

CT = computed tomography; EEG = electroencephalography; IQ = intelligence quotient; MRI = magnetic resonance imaging; PET = positron emission tomography.

Testing

Typically, doctors clip a sensor to the person's fingertip to measure the oxygen level in the blood (called pulse oximetry). They also measure blood sugar (glucose) levels and blood levels of any anticonvulsants the person is taking.

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 their physical examination are normal. For most other people, the following additional tests are usually done.

  • Blood tests to measure the alcohol level

  • Urine tests to check for drugs

  • Blood tests to check for HIV infection

Some doctors also routinely do blood tests to measure electrolyte levels and to evaluate kidney function.

Other tests are done based mainly on the symptoms and examination results (see Table: Some Causes and Features of Personality and Behavior Changes). They include

  • Computed tomography (CT) or magnetic resonance imaging (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 (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 women and people with a family history of thyroid disorders)

  • Chest x-ray, urinalysis and culture, a complete blood count, and blood cultures: If people have a fever

  • Blood tests to evaluate liver function: If people have symptoms of a liver disorder or a history of alcohol or drug abuse or if specific information about them is not available

Treatment

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 (see Default Surrogate Decision Making). 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.

Key Points

  • Not all changes in personality and behavior are due to mental disorders.

  • Other causes include drugs (including withdrawal and side effects), brain disorders, and bodywide disorders that affect the brain.

  • Doctors are particularly concerned about people with confusion or delirium, fever, headache, symptoms that suggest brain malfunction, or a recent head injury and about people who want to harm themselves or others.

  • Typically, doctors do blood tests to measure the levels of oxygen, sugar (glucose), and any drugs (such as anticonvulsants) the person is taking, and they may do other tests based on the symptoms and results of the examination.

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • LITHOBID