Seasonal affective disorder (winter depression) is a type of depression that recurs in the autumn and lasts until the spring. It is similar to regular depression except sufferers are usually very tired and have an increase in their appetite. It is more common in countries with few daylight hours in winter. One of the mainstays of treatment for all depression, including winter depression, are second-generation antidepressants (SGAs) such as selective serotonin reuptake inhibitors (SSRIs), and serotonin and norepinephrine reuptake inhibitors (SNRIs). It is not clear how well these drugs work for winter depression and how they compare to each other or to other types of therapy such as light therapy.