Effective posttonsillectomy analgesia is crucial for patient comfort and recovery. Fentanyl, notable for its potency, rapid action, and lipophilicity, has been successfully used in various procedures through multiple administration routes. However, the use of its nebulized form for posttonsillectomy pain has not been extensively explored. This study sought to compare the analgesic efficacy, onset time, and complications between nebulized and intravenous fentanyl in posttonsillectomy patients. In this randomized controlled trial, adult patients who underwent tonsillectomy were assigned to either an intravenous fentanyl group (1 mcg/kg) or a nebulized fentanyl group (4 mcg/kg). In both groups, fentanyl was administered when pain scores exceeded three. Pain levels were monitored every 5 minutes until they fell below four. The study also recorded the duration until the next analgesia request and noted complications (such as respiratory depression, bradycardia, chest tightness, drowsiness, nausea, pruritus, sweating, and flushing) within 24 hours. Patient exclusions were based on predetermined criteria. From an initial cohort of 59 patients, 22 in the intravenous group and 27 in the nebulizer group were eligible for analysis after applying the exclusion criteria. The nebulizer group exhibited a significantly prolonged period before the next analgesia request, with a median of 683.5 minutes (interquartile range 260-1440), in contrast to the 326.7 minutes (145.0-504.7) observed in the intravenous group (P = .009). The time to achieve a pain score less than 4 and the incidence of side effects did not differ significantly between the groups. Nebulized fentanyl provided a longer duration of analgesia than intravenous fentanyl in posttonsillectomy pain management, with similar onset times and side effect profiles. These findings underscore the potential of nebulized fentanyl as an effective alternative for pain control in posttonsillectomy patients.