Personality Changes: Causes and What to Do

What counts as a personality change

Everyone's mood varies, but personality (a person's typical way of thinking, feeling and behaving) is usually stable in adults. Concerning changes include:

• irritability, aggression or angry outbursts
• apathy: loss of motivation, interest or emotion
• disinhibition: rude, impulsive or socially inappropriate behavior
• loss of empathy and concern for others
• suspicion or paranoia
• new obsessions, rituals or changes in eating habits
• poor judgment, for example with money
• withdrawal from friends and activities
• confusion and fluctuating alertness

Sudden personality changes

A change over hours or days needs prompt medical attention because many causes are treatable and some are life-threatening.

• Delirium: an acute state of confusion and altered attention, common in older adults with infections (urinary infection, pneumonia), dehydration, surgery, new medicines, constipation or pain. Behavior may swing between agitation and drowsiness.
• Stroke: strokes affecting the frontal lobes or right side of the brain can change behavior with few other symptoms.
• Head injury: irritability, impulsiveness and mood swings after a concussion or more severe brain injury.
• Encephalitis and meningitis: brain infection or autoimmune inflammation, often with fever, headache, seizures or confusion. Autoimmune encephalitis can present in young people with psychiatric symptoms and memory loss.
• Drugs and alcohol: intoxication, withdrawal and reactions to steroids, sedatives, stimulants, Parkinson's medicines and others.
• Low blood sugar, low sodium and other metabolic problems.

Gradual personality changes

Mental health conditions

• Depression: irritability, withdrawal, low motivation and pessimism. In men and teenagers, irritability may be more prominent than sadness.
• Bipolar disorder: episodes of mania (reduced sleep, high energy, rapid speech, impulsiveness) alternating with depression.
• Psychosis and schizophrenia: withdrawal, odd beliefs, hallucinations and social decline, usually starting in the late teens or twenties.
• Substance use disorders.

Dementia

• Frontotemporal dementia: often starts between 45 and 65 with personality and behavior changes before memory loss: disinhibition, apathy, loss of empathy, compulsive behaviors and changes in food preferences.
• Alzheimer's disease: memory loss usually comes first, but anxiety, suspicion, irritability and withdrawal are common. See dementia.
• Lewy body dementia: fluctuating alertness, visual hallucinations and parkinsonism.
• Huntington's disease: irritability and impulsiveness with involuntary movements.

Other medical causes

• Brain tumor: especially in the frontal lobe, with headaches, seizures or weakness.
• Thyroid disease: hypothyroidism causes slowness and low mood; hyperthyroidism causes anxiety and irritability.
• Normal pressure hydrocephalus: apathy with walking problems and urinary urgency.
• Vitamin B12 deficiency, liver disease and chronic kidney disease.
• HIV, syphilis and other infections.
• Hormonal changes around menopause.

How doctors find the cause

Because the person may not recognize the change, doctors rely heavily on family members. Useful information includes when the change started, how quickly it developed, specific examples, alcohol and drug use, medicines, head injuries and family history.

The assessment usually includes:

• physical and neurological examination
• memory and thinking tests
• blood tests: blood count, sodium, calcium, glucose, kidney, liver and thyroid function, B12, and infection tests
• urine test in older adults
• brain imaging (CT or MRI)
• sometimes EEG, lumbar puncture or referral to a neurologist or psychiatrist

Treatment and support

Treatment depends on the cause:

• delirium: treating the infection, stopping problem medicines, fluids, and a calm, familiar environment
• depression and bipolar disorder: talking therapies and medicines
• stroke, tumors, infections: specific medical or surgical treatment
• dementia: medicines for some types, structured routines, carer support and safety planning
• hormone and vitamin problems: replacement treatment

For families, it helps to stay calm, avoid arguing with confused beliefs, keep routines predictable, look after legal and financial planning early, and seek support for yourself.

Frequently asked questions

What can cause a sudden personality change?

Sudden changes are often caused by delirium from an infection, dehydration or medicines, especially in older adults. Stroke, head injury, brain infection, low blood sugar, and drug or alcohol effects are other causes. A sudden change needs urgent medical assessment.

What causes personality changes in the elderly?

Common causes are delirium from urinary or chest infections, medicine side effects, depression, and dementia. Small strokes, thyroid problems, vitamin B12 deficiency and hearing or vision loss can also contribute. Many of these are treatable.

Can a head injury change your personality?

Yes. Injury to the frontal and temporal lobes can cause irritability, impulsiveness, mood swings, reduced empathy and poor judgment. Changes may improve over months with rehabilitation, but some can be lasting. Even a concussion can cause temporary irritability.

Which dementia causes personality change first?

Frontotemporal dementia typically begins with changes in personality and behavior, such as disinhibition, apathy, loss of empathy and compulsive behaviors, often before memory problems. It frequently starts between ages 45 and 65.