Background and Aims: Paravertebral block has been found to be a recommended method of analgesia for breast surgeries. We aimed to assess the efficacy of paravertebral block compared to morphine by means of the visual analogue scale (VAS), pain-related biomarkers, and reactive oxygen species (ROS) in adult patients undergoing breast cancer surgeries under general anesthesia. Methodology: Forty patients undergoing breast surgery with or without lymph outcome were randomly divided into two groups. Group M received general anesthesia with intraoperative injection morphine (0.1 mg/kg) and group P received general anesthesia with paravertebral block with 0.25% bupivacaine (0.3 ml/kg). The primary objective was to compare the postoperative pain using VAS at baseline, 2 hours, 24 hours, and 48 hours. Secondary objectives were to compare the levels of pain-related biomarkers and ROS in both the groups at baseline, 24 hours, and 48 hours and to study the correlation between the VAS and level of pain-related biomarkers and ROS. Results: There was no significant difference in the postoperative VAS scores in both the groups ( P = 0.252, 0.548, 0.488 at baseline, 24 hours, and 48 hours, respectively) and no significant difference in the mean biomarkers in both the groups. The mean VAS negatively correlated with biomarker levels at 24 hours and 48 hours, but the change in VAS after 24 hours and 48 hours did not significantly correlate with the change in the biomarkers. Conclusion: Paravertebral block is equally efficacious to intraoperative morphine for breast surgeries for postoperative analgesia. The biomarker levels were not significantly different when patients received paravertebral block or morphine.