Background Adding of an adjuvant to local anesthetics improves the quality of nerve block and reduces the need of postoperative analgesic intake. Aim The aim of this study was to compare the block characteristics of bupivacaine when used alone with those characteristics after using different adjuvants in ultrasoundguided supraclavicular brachial plexus block (US-guided SCBPB) in patients undergoing below shoulder upper limb surgeries. Patients and methods A prospective, double-blinded, randomized, controlled trial. A total of 108 patients undergoing elective upper limb surgeries under US-guided SCBPB were randomly allocated according to the studied solution into four equal groups (n=27): (i) Group C: 30 ml bupivacaine 0.5%+5 ml 0.9% saline. (ii) Group D: 30 ml bupivacaine 0.5% +100 μl dexmedetomidine diluted to 5 ml using 0.9% saline. (iii) Group N: 30 ml bupivacaine 0.5%+10 mg nalbuphine hydrochloride diluted to 5 ml using 0.9% saline. (iv) Group M: 30 ml bupivacaine 0.5%+5 ml of 10% MgSO4. We compared the onset and duration of sensory and motor blockade, hemodynamic stability, sedation, complications and postoperative analgesia. Results There were no significant differences in the times of onset of both sensory and motor blocks between the four groups. The analgesic duration and duration of motor block were significantly longer in all adjuvant groups. The total consumption of paracetamol during the first 24 h was significantly higher in group C. Patients in groups D and M had statistically significantly higher sedation scores at different times during the study. Conclusion Adding either dexmedetomidine, nalbuphine, or magnesium sulfate to bupivacaine in US-guided SCBPB prolongs both sensory and motor blockade. Both dexmedetomidine and magnesium sulfate produces significant sedation when added to bupivacaine. Keywords: brachial plexus, dexmedetomidine, magnesium sulfate, nalbuphine, supraclavicular