Persistent sadness that drains meaning from ordinary life is more than ordinary low mood. Depression as a clinical disorder involves sustained low mood, loss of interest or pleasure, and associated changes in sleep, appetite, energy, concentration, and self-worth.

Symptoms must persist for weeks and impair function for diagnosis. Causes involve genetic vulnerability, life stress, medical illness, and alterations in brain circuits and chemistry. Depression increases risk of suicide and worsens outcomes of concurrent physical diseases.

Effective treatments include psychotherapy, antidepressant medication, and, for severe or resistant cases, other somatic therapies. Primary-care screening and prompt referral improve detection. Recovery is realistic for most patients, though recurrence risk requires ongoing attention and sometimes maintenance treatment.

• Mood disorder with persistent sadness and loss of interest
• Affects sleep, energy, concentration, and self-worth
• Increases suicide risk and complicates physical illness
• Responds to therapy, medication, and combined approaches