Which personality disorder in the dramatic/erratic cluster is known for unstable moods and relationships?

The personality disorder in the dramatic/erratic cluster that is known for unstable moods and relationships is Borderline Personality Disorder. This disorder is characterized by a pervasive pattern of instability in interpersonal relationships, self-image, and affects. Individuals with Borderline Personality Disorder often experience intense emotional responses, leading to fluctuating relationships that can swing from extreme closeness to intense conflict. This mood instability is a hallmark of the disorder, causing individuals to experience feelings of emptiness, fear of abandonment, and identity disturbances.

In contrast, Narcissistic Personality Disorder primarily involves a sense of grandiosity and a need for admiration, focusing more on the individual's self-image than on unstable relationships. Histrionic Personality Disorder is characterized by excessive emotionality and attention-seeking behavior but does not necessarily lead to the kind of unstable relationships that define borderline disorder. Antisocial Personality Disorder involves a pattern of disregard for the rights of others and often results in manipulative or deceitful behavior rather than unstable emotional responses and relationships.

Thus, Borderline Personality Disorder stands out for its distinctive features related to mood variability and relationship instability.