Abstract
Borderline personality disorder (BPD) and treatment-resistant depression (TRD) are common mental disorders that are challenging to treat. Ketamine is an N-methyl-D-aspartate receptor antagonist that has shown promise as a rapid-acting antidepressant when administered intravenously. BPD symptoms have also been demonstrated to improve with repeated intravenous administration of ketamine, and a single case report described improvement in BPD following the intranasal administration of esketamine. We present a case report of a woman with BPD and TRD who responded to treatment with very low-dose sublingual ketamine. Very low-dose sublingual ketamine may be effective for the treatment of psychiatric disorders such as BPD and/or comorbid TRD.