The Hamilton Depression Rating Scale (HAM-D or HDRS) is one of the most widely used tools for evaluating the severity of depression in clinical and research settings. First developed in the 1960s by psychiatrist Max Hamilton, it was designed to provide a standardized assessment of depressive symptoms and treatment outcomes.

Unlike self-administered tools such as the PHQ-9, the HAM-D is administered by a trained clinician through structured interviews and observations. The scale typically contains 17 items, although versions with 21 and 24 items exist. It assesses a broad range of symptoms including mood, guilt, suicidal thoughts, insomnia, psychomotor changes, anxiety, weight loss, and somatic complaints.

The scoring system is weighted, with some items rated on a 5-point scale and others on a 3-point scale. The total score provides a measure of depression severity, ranging from mild to very severe. This makes it especially useful in clinical trials and psychiatric evaluations where precise monitoring is needed.