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 medication or losing a loved one), raises concern for a mental health issue.
(See also Overview of Mental Illness.)
Sudden changes in personality and behavior can be roughly categorized as involving one of the following types of symptoms:
Confusion or delirium
Delusions
Disorganized speech or behavior
Hallucinations
Mood extremes (such as depression or mania)
These categories are not specific mental illnesses. 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 general medical conditions or mental health issues.
People may have more than 1 type of change. For example, people with confusion due to a medication interaction sometimes have hallucinations, and people with mood extremes may have delusions.
Confusion and delirium
Confusion and 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.
Delirium often results from a serious, newly developed general medical problem or a reaction to a medication, especially in older adults. People who have delirium need immediate medical attention. If the cause of delirium is identified and corrected quickly, delirium often resolves.
Delusions
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 holy or are 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
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) or forming words (dysarthria) 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
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).
Hallucinations
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 health condition. Psychedelic drugs, 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. For example, before a seizure occurs, people may smell something when there is no smell (an olfactory hallucination).
Mood extremes
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 of Personality and Behavior Changes
Although people sometimes assume that changes in personality, thinking, or behavior are all due to a mental illness, there are many possible causes. All causes ultimately involve the brain, but dividing them into 4 categories can be helpful:
Psychological disorders
Substance use (including drug intoxication or withdrawal) and medication side effects
Disorders that affect mainly the brain
Bodywide (systemic) disorders that also affect the brain
Mental illnesses
Mental illnesses include
Dissociative disorders (when people feel detached from themselves or from the world around them)
Schizophrenia or other psychotic disorders
Somatic disorders (when psychological factors are expressed as physical symptoms)
Medications and illicit/recreational drugs
Substances or medications may affect personality or behavior when they cause
Intoxication: Particularly alcohol (when consumed in large amounts), amphetamines, , hallucinogens (such as LSD), and phencyclidine (PCP)
Withdrawal: Alcohol, barbiturates, benzodiazepines, and opioids
Side effects: Medications intended to affect brain function (including antiseizure medications, antidepressants, antipsychotics, sedatives, and stimulants), medications with anticholinergic effects (such as antihistamines), opioid pain relievers, and corticosteroids
Rarely, certain antibiotics and high blood pressure medications cause changes in personality and behavior.
Disorders that mainly affect the brain
These brain (neurologic) disorders can affect personality, mood, and behavior. They include
Brain infections, such as meningitis, encephalitis, and human immunodeficiency virus (HIV) infection that involves the brain (called HIV-associated encephalopathy)
Head injuries, such as a concussion and postconcussion syndrome
Bodywide disorders that also affect the brain
Bodywide (systemic) disorders that also affect the brain include
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 of Personality and Behavior Changes
During the initial evaluation, doctors try to determine whether symptoms are due to a mental illness or a general medical 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. These warning signs include
Symptoms that appear suddenly
Attempts to harm themselves or others or threats to do so
Confusion or delirium
Fever
Severe 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 seen by a health care professional 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 and psychiatric history. Doctors then do a physical examination, including a neurologic examination with a mental status examination (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).
Questions include when symptoms began. Many mental health conditions begin in a person's teens or 20s. If a mental health condition 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 general medical disorder. A general medical disorder is also more likely to be the cause when psychological symptoms change significantly during middle age or later in people with a chronic mental health condition. 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 a recreational or illicit 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 medication
Tremors: Parkinson disease or withdrawal of a medication
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 psychological or seizure disorder. If they have been treated, doctors ask whether they have stopped taking their medications or decreased the dose. However, because people with mental health conditions may also develop physical conditions, doctors do not automatically assume that any new abnormal behavior is caused by the mental health condition.
Doctors ask about general medical 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 psychological symptoms (such as multiple sclerosis).
During the physical examination, doctors look for signs of general medical disorders that can cause changes in mental status, particularly the following:
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 general medical condition. People with mental health conditions are rarely confused or delirious. However, many medical 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 health condition.
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). If doctors see swelling in part of the optic nerve (papilledema), pressure within the skull may be increased, and tumors or bleeding in the brain may be the cause of the mental symptoms.
Some Causes and Features of Personality and Behavior Changes
Cause | Common Features* | Tests |
|---|---|---|
Mental disorders | ||
Symptoms that occur in episodes lasting a few weeks to a few months and that include mania (abnormally elevated mood or energy level), depression, or both Episodes of mania:
Episodes of depression:
| A doctor's examination | |
Episodes of depression as described in bipolar disorder (see above) without a history of mania | A doctor's examination | |
Usually symptoms that develop slowly, at first with mildly disorganized thinking and difficulty coping with daily routines Later symptoms:
| A doctor's examination | |
Medications or Substance Use | ||
Use of an illicit or recreational drug, particularly | Agitation and sometimes panic or aggression Sometimes hallucinations With long-term use of alcohol:
With long-term use of amphetamines:
| A doctor's examination Sometimes blood or urine tests to detect the drug Sometimes EEG (which records the brain’s electrical activity) |
Withdrawal of a drug or medication, particularly | Typically significant confusion and delirium Shaking (tremors), headache, sweating, fever, and a rapid heart rate or palpitations Sometimes seizures, hallucinations, and sleep disturbances Onset after cutting down or stopping the drug | A doctor's examination Sometimes blood or urine tests to detect drugs |
Side effects of a medication | Vary, depending on the medication Medications with anticholinergic effects, such as
| A doctor's examination Sometimes stopping the medication to see whether the symptom goes away |
Brain (neurologic) disorders | ||
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 questions and tasks (neuropsychological testing) | |
Brain infections such as
| 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 |
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 in the brain (brain hemorrhage) | 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 |
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) | |
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) | 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 |
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 medications for diabetes | Tests to measure the blood sugar (glucose) level |
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 | |
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 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
| 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 B12 | 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. | ||
CT = computed tomography; EEG = electroencephalography; IQ = intelligence quotient; MRI = magnetic resonance imaging; PET = positron emission tomography. | ||
Testing
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 certain medications the person is taking (such as any antiseizure medications)
Urine tests to check for illicit and recreational drugs
A complete blood count (CBC)
Sometimes blood tests to measure electrolyte levels and to evaluate kidney or liver function
For most people known to have a mental illness, no further testing is needed if their only symptoms are a worsening of typical symptoms, if they are awake and alert, and if results of these tests and their physical examination are normal.
Other tests are done based mainly on the symptoms and examination results (see table Some Causes and Features of Personality and Behavior Changes). Tests may 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 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 tests to check for infection (cultures to check for bacteria in the bloodstream or tests for a viral infection): If people are very ill and have a fever
Treatment of Personality and Behavior Changes
If there is an underlying condition, it 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 or countries require that such decisions be made by someone appointed to make health care decisions for the mentally ill person (called a surrogate decision maker). 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 health conditions.
Other causes include substances (intoxication or withdrawal from illicit or recreational drugs), medication 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 as confusion or delirium, fever, and/or 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 medications (such as antiseizure medications) the person is taking, and they may do other tests based on the symptoms and results of the examination.
