Epidural injections (EIs) are the most commonly performed minimally invasive intervention in managing chronic low back pain (CLBP). There is inconsistency in data to accurately predict the degree of hypothalamic-piuitary-adrenal (HPA) axis suppression in patients receiving exogenous steroid therapy, especially in the form of epidural steroid injections (ESIs). We aim to quantify the degree and duration of HPA axis suppression after a single ESI of 80 mg methyl prednisolone acetate in patients with CLBP. A single open-label prospective study. An operating room of a tertiary care hospital. Patients with CLBP and unilateral radicular pain were included in this study. An ESI of 80 mg of methylprednisolone acetate was administered in each patient. Blood samples for cortisol and adrenocorticotropic hormone (ACTH) were collected before the ESI and on days 7, 14, and 28 after the ESI. The patients' pain levels were graded on the numeric rating scale (NRS) at baseline and on days 7, 14, 28, and 60 after the ESI in the pain clinic. A total of 30 patients were enrolled in this study. The median with interquartile range (IQR) serum cortisol level at baseline and on days 7, 14, and 28 after intervention were found to be 329.55 (208.49 - 399.48) nmol/L, 72.99 (52.95 - 119.82) nmol/L, 194.45 (73.88 - 292.52) nmol/L, and 302.56 (257.68 - 357.43) nmol/L, respectively. A significant discrease in the serum cortisol levels was observed on days 7 (P < 0.001) and 14 (P < 0.001). Twenty-six (87%), 13 (43%), and 2 (7%) patients had serum cortisol levels below normal (<170 nmol/L) on days 7, 14, and 28, respectively. HPA axis suppression was observed in all of the patients for a median (IQR) period of 14 days (range: 11-17 days). This study was an unblinded observational study. The effect of a single ESI was studied and the sample collection of day 21 serum cortisol and ACTH were passed over. HPA axis function was suppressed after the ESI until day 14 and returned to the normal range by postoperative week 4. Epidural injections, steroids, HPA, suppression, cortisol, ACTH.