Any disease of the mind; the psychological state of someone who has emotional or behavioral problems serious enough to require psychiatric intervention.
A mental illness is an illness of the mind. People with a mental illness may behave in strange ways, or have strange thoughts, in their view or the view of others. Mental illnesses develop during the life of a person. This may be linked to genes and experience. What is considered as a mental illness has changed over time. What is considered to be a mental illness may not be one in a different culture.
People with a mental illness sometimes have problems dealing with other people, or leading what is called a normal life. Treatment and certain medications can help people with certain mental illnesses lead a better life.