Depression causes sadness or loss of interest in or enjoyment of life to a degree that interferes with daily activities. It is a medical condition, not a normal reaction to such life situations as the death of a loved one or the loss of a job. About 1 of every 5 people experiences depression at some time in his or her life, and it is common among patients who see primary care providers. Common symptoms are lack of energy, change in sleep or appetite, and prominent thoughts of worthlessness or guilt. Sometimes the condition goes away on its own, but many people with depression need treatment with counseling or medication to speed recovery. Treating depression can be difficult. Treatment strategies that involve collaboration between primary care doctors and mental health specialists have been shown to improve depression outcomes. However, such strategies have been difficult to implement outside of research settings.