Once-monthly paliperidone palmitate (PP1M) is a long-acting injectable antipsychotic approved for the treatment of schizophrenia and schizoaffective disorder (SCA) in adults. To assess treatment patterns and schizophrenia/SCA-related hospitalization following payer rejection, patient reversal, or payment of an initial PP1M claim. This was a retrospective cohort study using the IQVIA Formulary Impact Analyzer database linked to the Medical Claims, Hospital Charge Detail Master, and Experian consumer databases. Patients with schizophrenia/SCA and ≥1 PP1M pharmacy claim from January 1, 2018, to February 28, 2022, were identified and stratified into 3 cohorts based on the transaction status of the initial PP1M claim (index date): rejected (payer not approved), reversed (payer approved, patient abandoned), and paid (payer approved, patient filled). Patient characteristics during the 12 months before the index date, subsequent treatment patterns, and schizophrenia/SCA-related hospitalization for patients with >6 months of follow-up were assessed by cohort. The rejected, reversed, and paid cohorts included 1,260, 1,046, and 1,686 patients, respectively. Across these cohorts, the mean ages ranged between 39.2 and 44.5 years; more than half were male (50.8%-51.6%) and White (50.6%-58.3%); 19.8%-24.6% of patients had a Quan-Charlson Comorbidity Index score of ≥2. Rates of prior atypical oral and long-acting injectable antipsychotic use ranged between 76.4%-80.3% and 7.8%-12.7%, respectively. Among patients with ≥6 months of follow-up, 52.2% in the rejected and 53.1% in the reversed cohorts had a subsequent paid PP1M claim during the study period; the median (quartile 1-quartile 3) time to the first paid PP1M claim was 22 (5-74) days for rejection and 11 (1-41) days for reversal. In the rejected and reversed cohorts, 10.2% (n = 111) and 9.8% (n = 90) of patients, respectively, did not receive any paid claim for an antipsychotic after the initial PP1M rejection/reversal. The prevalence of schizophrenia/SCA-related hospitalization during follow-up was similar between patients with a paid (7.4%) and rejected PP1M claim (7.0%; P = 0.689) but higher among patients with a reversed claim (10.8%; P = 0.004). After adjusting for confounders, patients in the reversed cohort were 39% more likely to have a schizophrenia/SCA-related hospitalization than those in the paid cohort (odds ratio = 1.39; 95% CI = 1.03-1.87). Payer rejection and patient reversal of initial PP1M claims is a form of primary nonadherence and may influence patient trajectory. Data from this study suggest that patient reversal of PP1M may lead to an increased risk of schizophrenia/SCA-related hospitalizations, potentially caused by missed or delayed treatment. Policy initiatives that remove barriers to primary adherence or fulfillment may help improve patients' clinical outcomes.