Symptoms include impairment of thinking, delusions and changes in behavior. Its onset is usually in the late teens or early twenties. The affective disorders are the most common psychiatric disorders. The primary disturbance is that of affect or mood. The causes of mental illnesses are not well understood, although it is believed that the functioning of the brain's neurotransmitters is involved.
More research is needed to determine causes and to plan strategies of prevention.
While the current medications do not cure these illnesses, they can reduce the symptoms markedly for most people.