BACKGROUND: Paliperidone is among the most cost-effective antipsychotics in adults with schizophrenia, and it has different formulations, including oral paliperidone extended-release (ER) and long-acting injectable (LAI) paliperidone formulations administered every month (PP1M), 3 months (PP3M), or 6 months (PP6M). However, cost-effectiveness analyses comparing different paliperidone formulations were limited. OBJECTIVE: To compare the cost-effectiveness across different paliperidone formulations. METHODS: A Markov model was developed to simulate 1,000 adults aged 40 years with stable schizophrenia transitioning among stable disease-medication adherent, stable disease-medication nonadherent, relapse with hospitalization, relapse with ambulatory care, and death states every 3 months for 5 years. Drug costs were estimated using the prices listed in the Veterans Affairs Federal Supply Schedule, and costs for treating complications were estimated from published studies. All costs were estimated from the US health care system perspective and standardized to 2022 US dollars using the Consumer Price Index Inflation Calculator. Quality-adjusted life-years (QALYs) were estimated using relapse rates from randomized clinical trials and health-related quality of life scores from observational studies. The estimated future costs and QALYs were discounted at 3%. We reported incremental net monetary benefits between alternative formulations at the $50,000 willingness-to-pay (WTP) threshold with a positive value indicating cost-effectiveness. The impact of parameter uncertainty on study outcomes was assessed using 1-way deterministic and probabilistic sensitivity analyses. RESULTS: In adults with schizophrenia stabilized with paliperidone ER, switching to LAI formulations was associated with increased QALY (PP1M = 0.05, PP3M = 0.14, PP6M = 0.15) and increased cost (PP1M = 49,433, PP3M = 26,698, PP6M = 26,147), leading to a negative incremental net monetary benefit (PP1M = -$46,804, PP3M = -$19,508, PP6M = -$18,886) compared with continuing ER. Among LAI formulations, PP6M was cost-saving with the most QALYs gained (cost = $63,277, QALY = 3.731), followed by PP3M (cost = $63,828, QALY = 3.729) and PP1M (cost = $86,563, QALY = 3.638). At the $50,000 WTP threshold, the probabilities for PP1M, PP3M, and PP6M being cost-effective compared with paliperidone ER were 0.4%, 10.2%, and 9.8%, respectively. The probability of PP6M being cost-effective was 92.6% for the PP6M-PP1M pair and 55.2% for the PP6M-PP3M pair, and 91.1% of PP3M use was cost-effective in the PP3M-PP1M pair. The results were generally robust in the sensitivity analyses, even at the $190,000 WTP threshold. CONCLUSIONS: For patients with schizophrenia stabilized with paliperidone ER, switching to LAI formulations was not cost-effective, suggesting the high drug costs for LAI may not justify the improved quality of life within 5 years. Among LAI formulations, PP6M was cost-effective over PP1M and PP3M.