Objectives: Non-adherence to medication is common in the adult ADHD clinical group. The goal of this pre-registered study was to examine whether the DSM-5 Alternative Model of Personality Disorder (AMPD), generality personality dysfunction (LPFS-BF 2.0) or maladaptive personality traits (PID-5), can predict time to premature discontinuation of pharmacological treatment beyond other known factors. Methods: A sample of 284 adult patients with ADHD (60.6% female; M[subscript age] = 32.31 years) were investigated for medication adherence from 2018 to 2023, using time-to-event analytic methods. Results: Of the sample, 54 were found to have discontinued treatment prematurely without consulting their physician. Interestingly this group was prescribed considerably lower doses before discontinuation than adhering patients. General personality dysfunction and maladaptive antagonistic personality traits are implicated in varying degrees, with the specific maladaptive personality facets "Intimacy Avoidance and Deceitfulness" (PID-5) significantly predicting time to premature discontinuation of ADHD medication beyond other known reasons for non-adherence. Conclusions: The broader implication is that the emerging personality pathology models hold promise to predict non-adherence in the adult ADHD population.