Impact of comorbid borderline personality disorder on medication exposure and healthcare utilisation in bipolar disorder

Background

Bipolar disorder (BD) and borderline personality disorder (BPD) frequently co-occur and are associated with worse outcomes, including greater symptom severity, increased relapse rates, and a more complex clinical course[1]. Although pharmacological treatment represents the cornerstone of BD management, no medications are specifically approved for BPD, and treatment in this population is often characterised by complex and heterogeneous prescribing patterns[2]. In individuals with BD, comorbid BPD may contribute to greater treatment intensity and polypharmacy. However, evidence on pharmacological exposure and healthcare utilisation in this population remains limited. This population-based study aimed to investigate whether comorbid BPD in individuals with BD (BD/BPD) was associated with greater psychotropic medication burden, more complex treatment patterns, and increased healthcare utilisation.

Methods

Health records from individuals with BD were extracted from the PADRIS-PRESTO public healthcare registry (2010–2019), a program that integrates anonymized sociodemographic, clinical, and healthcare utilisation data from the Catalan public healthcare system[3]. Patients were classified as BD alone or BD/BPD based on International Classification of Diseases, Tenth Revision (ICD-10) diagnostic codes. Pharmacological exposure was quantified using defined daily doses per year (DDD/year). Differences between groups were examined in terms of treatment complexity and healthcare utilisation, including psychiatric hospitalizations, specialized mental health outpatient visits, and emergency visits. Treatment complexity was defined as the number of concurrent medications per month and the proportions of patients receiving monotherapy and three or more medications. Group comparisons were performed using t-tests and χ² tests. A multivariable linear regression model was used to assess the association between BD/BPD and total DDD/year, adjusting for sex, age, index year, socioeconomic status, medical comorbidity count, concurrent drug number, and healthcare utilisation.

Results

The cohort included 24,135 individuals with BD: 1,613 with BD/BPD and 22,522 with BD alone. In the regression model, comorbid BPD was significantly associated with greater total DDD/year (β = 106.10 DDD/year, 95% CI 61.19–151.01; p < 0.001). Compared with BD alone, individuals with BD/BPD had a higher mean number of concurrent medications per month (2.21 ± 0.81 vs 1.86 ± 0.67; p < 0.001), a lower proportion of monotherapy (30.7% vs 50.8%; p < 0.001), and a higher proportion of regimens involving three or more medications (28.2% vs 16.5%; p < 0.001). They also showed higher healthcare utilisation, including psychiatric hospitalisations (0.46 ± 0.82 vs 0.21 ± 0.52), specialised mental health outpatient visits (9.66 ± 11.98 vs 6.07 ± 6.27), and emergency visits (1.37 ± 2.57 vs 0.65 ± 1.16; all p < 0.001).

Conclusions

Comorbid BPD in BD is associated with greater pharmacological burden, independently of demographic, clinical and service-use factors. Moreover, patients with comorbid BPD showed greater treatment complexity and higher healthcare utilisation. These findings support the view of BPD as a clinically relevant modifier of illness complexity in BD, contributing to increased treatment intensity beyond markers of severity captured in routine data.

References

1. Temes, C.M., Boccagno, C., Gold, A.K., Kobaissi, H., Hsu, I., Montinola, S., Sylvia, L.G., 2024. Comorbidity of bipolar disorder and borderline personality disorder: Phenomenology, course, and treatment considerations. Bipolar Disord 26, 548–555. https://doi.org/10.1111/bdi.13465.
2. Tennant, M., Frampton, C., Mulder, R., Beaglehole, B., 2023. Polypharmacy in the treatment of people diagnosed with borderline personality disorder: repeated cross-sectional study using New Zealand’s national databases. BJPsych Open 9, e200. https://doi.org/10.1192/bjo.2023.592.
3. De Prisco, M., Oliva, V., Fico, G., Mas, A., Valenzuela-Pascual, C., Montejo, L., Bort, M., Sommerhoff, C., Bortolozzi, A., Miquel-Rio, L., Vilella, E., Forte, M.F., Fortea, L., Fernández, T., Giménez-Palomo, A., Sague Vilavella, M., Madero, S., Llorca Bofí, V., Bioque, M., Grande, I., Murru, A., Pacchiarotti, I., Cavero, M., Blanch, J., Viñas-Bardolet, C., Aparicio-Nogué, V., Martínez-Cerdá, J.F., Parellada, E., Martínez-Arán, A., Radua, J., Vieta, E., Hidalgo-Mazzei, D., Anmella, G., 2025. The PADRIS-PRESTO cohort: A comprehensive population-based study on mental health in Catalonia. Eur Psychiatry 68, e144. https://doi.org/10.1192/j.eurpsy.2025.10103.