Intentional and unintentional medication non-adherence in psoriasis: the role of patients' medication beliefs and habit strength.

Medication non-adherence is a missed opportunity for therapeutic benefit. We assessed 'real-world' levels of self-reported non-adherence to conventional and biologic systemic therapies used for psoriasis and evaluated psychological and biomedical factors associated with non-adherence using multivariable analyses. Latent profile analysis (LPA) was used to investigate whether patients can be categorised into groups with similar medication beliefs. LPA categorises individuals with similar profiles on a set of continuous variables into discrete groups represented by a categorical latent variable. 811 patients enrolled in the British Association of Dermatologists Biologic Interventions Register (BADBIR) were included. 617 patients were using a self-administered systemic therapy; 22.4% were classified as 'non-adherent' (12% intentionally and 10.9% unintentionally). Patients using an oral conventional systemic agent were more likely to be non-adherent compared to those using etanercept or adalimumab (29.2% vs. 16.4%; p ≤ 0.001). LPA supported a 3-group model; all groups held strong beliefs about their need for systemic therapy but differed in levels of medication concerns. Group 1 (26.4% of the sample) reported the strongest concerns, followed by Group 2 (61%), with Group 3 (12.6%) reporting the weakest concerns. Group 1 membership was associated with intentional non-adherence (odds ratio (OR) 2.27; 95% confidence interval: 1.16 - 4.47) and weaker medication-taking routine or habit strength was associated with unintentional non-adherence (OR 0.92; 95% CI: 0.89 - 0.96). Medication beliefs and habit strength are modifiable targets for strategies to improve adherence in psoriasis.