Anhedonia is a term in psychiatry used to describe the inability to feel pleasure from activities that are usually enjoyable, such as hobbies, social interaction and sex. It is a symptom of many forms of mental illness, including clinical depression and schizophrenia. However, it can often just be a reaction to stress or severe illness, although it is also exhibited as a symptom of certain physical illnesses such as Familial Mediterranean fever. The underlying etiology of anhedonia is unknown, although it is thought to be related to the function of dopamine.