Background Comparing bupivacaine's adjuvants in spinal anesthesia, we assessed the specific blocking characteristics and adverse effects of bupivacaine alone and in combination with dexmedetomidine or meperidine in spinal anesthesia during cesarean section. Methods In this double-blind randomized clinical trial study, ninety pregnant women were divided into groups to receive 10 mg bupivacaine (group B), 10 mg bupivacaine with 5 μg dexmedetomidine (group BD), or 10 mg bupivacaine with 10 mg meperidine (group BM) intrathecal. Patients were assessed for the quality of analgesia during operations. Durations of sensory and motor blocks and anesthesia-related complications were analyzed using SPSS 21, and p values <0.05 were considered statistically significant. Results The onset of sensory and motor blocks was essentially the same in all treated groups. Block regression time was significantly prolonged in the BD group compared to the B and BM groups (p < 0.001). The duration of analgesia was significantly longer in the BD and BM groups than in the B group (p < 0.001). The level of sedation in the BD group was higher than in the B group. Shivering occurred in 40% of patients in the B group, which was significantly more than that of the BD (16.6%) and BM (33.3%) groups. Itching happened in 33.3% of women in the BM group which was statistically more than that of the B (3.33%) and BD (0) groups. The incidence of adverse effects was the same in all groups. Conclusion The combination of bupivacaine with dexmedetomidine significantly prolonged sensory and motor regression time and duration of analgesia.