This randomized controlled trial titled “Comparative study of duration of postoperative analgesia with intrathecal versus subcutaneous dexmedetomidine as an adjuvant to 0.5% hyperbaric bupivacaine in lower limb surgeries” aims to evaluate the effectiveness of two routes of dexmedetomidine administration in prolonging postoperative analgesia. The study will be conducted in the Department of Anaesthesiology, Jubilee Mission Medical College and Research Institute, Thrissur, over a period of 18 months. Thirty adult patients aged 18–60 years, belonging to ASA physical status I or II and scheduled for elective lower limb surgeries under spinal anesthesia, will be enrolled and randomly allocated into two groups of fifteen each using computer-generated randomization. Group A will receive 3 mL of 0.5% hyperbaric bupivacaine with 5 µg intrathecal dexmedetomidine and subcutaneous normal saline, while Group B will receive 3 mL of 0.5% hyperbaric bupivacaine intrathecally and 0.5 µg/kg dexmedetomidine subcutaneously. Both the anesthesiologist and the patient will be blinded to group allocation. The primary outcome of the study will be the duration of postoperative analgesia, measured as the time to first request for rescue analgesia. Secondary outcomes include hemodynamic stability, onset and duration of sensory and motor block, incidence of adverse effects such as bradycardia, hypotension, and nausea, total analgesic requirement within 24 hours, and patient satisfaction scores. Data will be analyzed using SPSS version 24, with results expressed as mean ± standard deviation for continuous variables and percentages for categorical variables. Statistical tests such as the independent t-test and chi-square test will be used, and a p-value less than 0.05 will be considered significant. This study seeks to determine whether subcutaneous dexmedetomidine provides analgesic efficacy comparable to intrathecal administration, potentially offering a simpler and safer alternative route for postoperative pain management following lower limb surgeries.