Objective: The aim was to better understand how beliefs influence medication adherence in asthma. Methods: All participants were prescribed an inhaled corticosteroid for a diagnosis of asthma. Each participant completed a survey consisting of: Beliefs about Medicines Questionnaire (BMQ), Brief-Illness Perception Questionnaire (B-IPQ) and Multi-dimensional Health Locus of Control Scale (MHLCS). Adherence to inhaled corticosteroids was elicited using the Medication Adherence Report Scale (MARS). Multiple linear regression with interaction effects was used to identify significant predictors of medication adherence and interactions between beliefs. Results: A total of 198 participants completed the survey. The mean($±$SD) MARS score was 19.2($±$4.5). A multivariable model (adjusted R2 = 0.39) predicted adherence using: age, asthma hospitalisation, timeline (B-IPQ) subscale, necessity and concern (BMQ) subscales, doctor (MHLCS) subscale and the two interaction effects (concerns [BMQ] moderated by chance [MHLCS] and treatment control [B-IPQ] moderated by understanding [B-IPQ]). Conclusion: The findings of this study contribute to a better understanding of the role of beliefs in medication adherence in asthma. Certain beliefs meaningfully interrelate and change the relationship they have with medication adherence. Practice Implications: If these beliefs are causally related to medication adherence and can be intervened upon, the findings are useful for providing targets to personalise adherence support.