The cause of anxiety disorders is thought to be a combination of genetic and environmental factors. Risk factors include a history of child abuse, family history of mental disorders, and poverty. Anxiety disorders often occur with other mental disorders, particularly major depressive disorder, personality disorder, and substance use disorder. To be diagnosed, symptoms typically need to be present for at least six months, be more severe than the symptoms that would normally be expected for certain situations, and decrease a person's ability to function in their daily life. Other problems that may result in similar symptoms include hyperthyroidism; heart disease; caffeine, alcohol, or cannabis use; and withdrawal from certain drugs, among others. Anxiety disorders differ from normal fear or anxiety by being excessive or persisting.