The observation of strange behavior depends at least in part upon the perceptions of the observer. For most people, behaviors that are observed as out of the ordinary or strange are a feature of psychotic disorders, mood disorders, and other mental-health conditions. Examples of conditions in which psychosis (altered perception of reality) are present include schizophrenia, delusional disorder, and schizoaffective disorder. People suffering from psychosis may have an altered perception of reality that often affects their behavior, leading them to act in ways that may be perceived as strange. Problems controlling one's behavior can also occur as a result of brain damage or disorders. People suffering from dementia may display strange behaviors. Behavioral changes can be accompanied by other psychiatric symptoms or by physical symptoms if they are related to a medical condition. Substance abuse and drug overdoses can also lead to problems with behavior.
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.
Pictures, Images, Illustrations & Quizzes
Alzheimer's Disease Symptoms & Early Diagnosis
Learn the early warning signs and symptoms of Alzheimer's disease. Memory loss and confusion can be signs of normal aging, but...
Autism Signs in Children: What Is Autism Spectrum Disorder?
What is autism? Learn about the signs, symptoms, and diagnosis of autism spectrum disorder. Get information about the causes of...
Bipolar Disorder: Symptoms, Testing for Bipolar Depression
Bipolar disorder (once called manic depression) causes extreme mood shifts and can be disorienting. Our experts define bipolar...
Dementia, Alzheimer's Disease, and Aging Brains
What is dementia? Learn about dementia disorders such as Lewy Body Dementia, Alzheimer's disease (AD), Vascular (multi-infarct)...
Panic Attacks (Panic Disorder) Quiz: Test Your Mental Health IQ
Could you suffer a panic attack? Take this Panic Attacks Quiz to learn causes, symptoms, and treatments for panic disorder. Use...
Parkinson's Disease: Symptoms, Causes, Stages, Treatment
Discover the symptoms, causes, stages, and treatment options for Parkinson's disease. Learn more about the stages of Parkinson's...
Schizophrenia: Symptoms, Types, Causes, Treatment
What is schizophrenia? Learn about schizophrenia symptoms, signs, and treatment. Read about schizophrenia types such as paranoid...
Stroke Causes, Symptoms, and Recovery
What is a stroke? Learn about stroke symptoms like sudden numbness or weakness, confusion, vision problems, or problems with...
Teen Drug Abuse: Warning Signs, Statistics, and Facts
Teen drug abuse is a growing concern today. Learn statistics, facts, warning signs, and effects related to teen substance abuse...
Causes of Unusual Behavior
Alcoholism is a disease that includes alcohol craving and continued drinking despite repeated alcohol-related problems, such as...
Alzheimer's disease is a common cause of dementia. Symptoms and warning signs of Alzheimer's disease include memory loss,...
Anxiety is a feeling of apprehension and fear characterized by symptoms such as trouble concentrating, headaches, sleep problems,...
Autism Spectrum Disorder (In Children and Adults)
Autism in children and adults is a developmental disorder, characterized by impaired development in communication, social...
Bipolar disorder (or manic depression) is a mental illness characterized by depression, mania, and severe mood swings. Treatment...
Brain and Spinal Cord Tumors in Adults (Symptoms, Signs, Causes, Treatment Options, Life Expectancy)
Brain and spinal tumor are diseases in which cancer (malignant) cells begin to grow in the tissues of the brain. Tumors that...
Brain Tumor (Symptoms, Signs, Types, Causes, Survival Rates)
A brain tumor can be either non-cancerous (benign) or cancerous (malignant), primary, or secondary. Common symptoms of a primary...
Dementia is defined as a significant loss of intellectual abilities such as memory capacity, severe enough to interfere with...
Depression is an illness that involves the body, mood, and thoughts and affects the way a person eats and sleeps, the way one...
Drug addiction is a chronic disease that causes drug-seeking behavior and drug use despite negative consequences to the user and...
Dysthymia is a less severe form of chronic depression. Symptoms and signs include insomnia, suicidal thoughts, guilt, empty...
Human Immunodeficiency Virus (HIV)
The human immunodeficiency virus (HIV) causes HIV infection and the acquired immunodeficiency syndrome (AIDS). Symptoms and signs...
Huntington's disease is the result of degeneration of neurons in areas of the brain. Huntington's disease is an inherited...
Panic attacks are sudden feelings of terror that strike without warning. These episodes can occur at any time, even during sleep....
Parkinson's disease is a slowly progressive neurological disease characterized by a fixed inexpressive face, a tremor at rest,...
Phobias are unrelenting fears of activities (social phobias), situations (agoraphobia), and specific items (arachnophobia). There...
Postpartum depression is a form of depression that occurs within a year after delivery. It is thought that rapid hormone changes...
Posttraumatic Stress Disorder
Post-traumatic stress disorder (PTSD), a psychiatric condition, can develop after any catastrophic life event. Symptoms include...
Psychotic disorders are a group of serious illnesses that affect the mind. Different types of psychotic disorders include...
Schizoaffective disorder is a mental illness that features schizophrenia and a mood disorder, either major depression or bipolar...
Schizophrenia is a disabling brain disorder that may cause hallucinations and delusions and affect a person's ability to...
Schizotypal Personality Disorder
Schizotypal personality disorder is characterized by odd behaviors, feelings, perceptions, and ways of relating to others that...
Seasonal Affective Disorder (SAD)
Seasonal affective disorder is a type of depression that tends to occur as the days grow shorter in the fall and winter. Symptoms...
Epilepsy is a brain disorder in which the person has seizures. There are two kinds of seizures, focal and generalized. There are...
Stroke (Signs, Symptoms, Warning Signs)
A stroke is an interruption of the blood supply to part of the brain caused by either a blood clot (ischemic) or bleeding...
Other Causes of Unusual Behavior
- Brain Trauma
- Catastrophic Life Events
- Conduct Disorder
- Delusional Disorder
- Drug-Induced Psychosis
- Oppositional Defiant Disorder
Examples of Medications for Unusual Behavior
- aripiprazole (Abilify, Abilify Maintena, Aristrada)
- bupropion (Wellbutrin, Wellbutrin SR, Wellbutrin XL, Zyban, Aplenzin, Fortivo XL, Zyban)
- chlorpromazine - oral, Thorazine
- chlorpromazine-injection, Thorazine
- citalopram, Celexa
- clozapine (Clozaril, Fazacio ODT, Versacloz)
- desvenlafaxine (Pristiq, Khedezla)
- duloxetine, Cymbalta
- fluoxetine, Prozac, Sarafem, Prozac Weekly
- fluphenazine (Permitil, Prolixin)
- fluphenazine concentrate - oral, Prolixin
- fluphenazine liquid - oral, Prolixin
- haloperidol (Haldol)
- Lexapro (escitalopram)
- olanzapine, Zyprexa, Zydis, Zyprexa Relprevv
- paroxetine, Paxil, Paxil CR, Pexeva
- quetiapine (Seroquel, Seroquel XR)
- risperidone, Risperdal; Risperdal Consta, Risperdal M-TAB
- Sertraline (Zoloft)
- thiothixene - oral, Navane
- venlafaxine, Effexor XR (Effexor has been discontinued in the US)
- ziprasidone (Geodon)