Beliefs About Medicines and Adherence to Biologic Therapy in Patients with Moderate-to-Severe Psoriasis: A Cross-Sectional Study

<i>Background and Objectives</i>: Psoriasis is a chronic, immune-mediated inflammatory dermatosis affecting approximately 125 million people worldwide. Biologic therapy (BT) has significantly improved treatment outcomes for moderate-to-severe psoriasis, but real-world adherence to these therapies is not fully understood. This study aimed to evaluate adherence to BT among patients with moderate-to-severe psoriasis and examine how general and treatment-specific beliefs about BT are associated with adherence. <i>Materials and Methods</i>: This cross-sectional study was conducted from March to August 2025 at the University Hospital of Split, Croatia. A total of 122 adults with moderate-to-severe psoriasis receiving interleukin-17 or interleukin-23 inhibitors completed validated Croatian versions of the Beliefs about Medicines Questionnaire-General (BMQ-G), Beliefs about Medicines Questionnaire-Specific (BMQ-S), and the Medication Adherence Report Scale (MARS-5). Adherence was assessed using MARS-5, and beliefs were analyzed using BMQ-G, BMQ-S, and the Necessity-Concerns Framework. Correlation and group-based analyses were used to explore associations between beliefs, adherence, and sociodemographic factors. <i>Results</i>: Adherence to BT was high, with 96.7% of participants reporting that they use their medication as prescribed and 84.4% stating they always followed dosing instructions. Most participants endorsed strong necessity beliefs regarding BT; however, concerns remained common-40.2% reported worry about long-term effects and 15.6% about dependence. General beliefs about medicines influenced treatment-specific perceptions: BMQ-G Overuse scores were negatively correlated with adherence (r = -0.27; <i>p</i> = 0.003) and positively correlated with BMQ-Specific concerns. Participants classified as Distrustful (low necessity, high concerns) made up 31.1% of the cohort and had the highest Harm and Overuse scores. Lower educational attainment was associated with stronger negative beliefs about medicines. <i>Conclusions</i>: Although adherence to BT was high, a considerable proportion of patients expressed residual concerns, especially those with more negative general beliefs about medicines. These findings underscore the importance of assessing medication beliefs in routine care. Tailored education and communication strategies may help address concerns and support long-term adherence to BT in psoriasis.