Introduction: Adding adjuvant drugs to intrathecal local anesthetics improves the quality and duration of the sensory blockade and prolongs postoperative analgesia. Intrathecal opioids are synergistic with local anesthetics, thereby intensifying the sensory block without increasing the sympathetic block. This study was designed to comparatively evaluate the two different dosages of nalbuphine as intrathecal adjuvants on subarachnoid block (SAB) characteristics of 0.5% hyperbaric bupivacaine. Methods: A randomized, triple arm study was conducted on 60 adult female patients with American Society of Anesthesiologists physical status I and II, aged 30-60 years, scheduled for total abdominal hysterectomy under SAB. Patients were randomized into three groups: group I received 15 mg of 0.5% hyperbaric bupivacaine, group II received 15 mg of 0.5% hyperbaric bupivacaine with 1.6 mg of nalbuphine, and group III received 15 mg of 0.5% hyperbaric bupivacaine with 2.4 mg of nalbuphine. The primary outcome was the duration of analgesia, while secondary outcomes included onset, duration of sensory and motor block, maximum cephalic extension, and two dermatome segment regressions. Results: The onset time of the sensory block was 3.2 ± 1.0 minutes, 3.5 ± 1.6 minutes, and 3.1 ± 1.1 minutes in groups I, II, and III, respectively. The onset time of the motor block was 8.5 ± 1.0 minutes, 8.5 ± 1.1 minutes, and 8.2 ± 1.1 minutes in groups I, II, and III, respectively. The onset of sensory and motor blocks was comparable among the three groups with no statistically significant difference (p > 0.05). The total duration of analgesia was 117.8 ± 23.3 minutes, 166.8 ± 27.8 minutes, and 181.8 ± 25.9 minutes in groups I, II, and III, respectively, with a statistically significant difference. Few incidences of manageable hypotension, but no incidences of bradycardia or respiratory insufficiency, occurred. Five patients of the control group shivered, which was managed well by tramadol 50 mg and ondansetron 4 mg. No patient suffered from pruritus, sedation, respiratory depression, nausea, and vomiting. Conclusion: The study concluded that intrathecal nalbuphine in a 1.6 mg dose is an effective adjuvant to 0.5% hyperbaric bupivacaine for SAB. It potentiated the SAB characteristics and enhanced the duration of analgesia with no effect on respiration. Nalbuphine in a dose of 2.4 mg did not offer any added advantage.