Methylphenidate treatment in adults with comorbid attention-deficit/hyperactivity disorder and borderline personality disorder: a prospective longitudinal study.

Attention-deficit/hyperactivity disorder (ADHD) and borderline personality disorder (BPD) frequently co-occur. However, evidence on the clinical effects of stimulant treatment in ADHD-BPD comorbidity remains limited. This prospective study aimed to investigate the longitudinal effects of methylphenidate (MPH) on borderline personality features in adults with ADHD-BPD. Thirty-six adults diagnosed with ADHD who also met the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition criteria for BPD were treated with MPH and followed for at least 16 weeks. Clinical ratings of the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition BPD criteria and psychometric measures assessing symptom severity and personality functioning were obtained at baseline and follow-up. Twenty-four participants (66.7%) completed the follow-up. Follow-up duration ranged from 3.9 to 12.3 months, with a mean duration of 7.8 ± 2.48 months. The number of BPD criteria significantly decreased after treatment ( r  = 0.82, P  < 0.001). Nineteen participants no longer met the diagnostic threshold for BPD, and 10 achieved remission (≤2 BPD criteria). Baseline anger dysregulation ( P  = 0.009) and mood stabilizer use ( P  = 0.029) were associated with continued MPH treatment. Our findings preliminarily suggest that MPH, especially combined with mood stabilizers, may be associated with clinical benefits and acceptable tolerability in patients with comorbid ADHD-BPD. While causal conclusions cannot be drawn, replication in randomized controlled trials is warranted.