Several strategies for discovering drugs from unexplored natural products continue to strengthen research and development with current commercial evidence supporting their applications. We assessed the effects of the hydroethanolic extract of root (HEASR) against phenylhydrazine (PHZ)-induced haematotoxicity, biochemical changes, and oxidative stress in male Wistar rats. Groups 1 and 2 controls received normal saline (10 mL/kg/day) and PHZ (60 mg/kg, day 4 and 5), respectively, via oral gavage. Groups 3, 4, and 5 were administered dexamethasone (DXM, 0.014 mg/kg/day, p.o.), HEASR1 (50 mg/kg/day, p.o.) and HEASR2 (200 mg/kg/day, p.o.), respectively. Groups 6, 7, and 8 received HEASR2 (200 mg/kg/day), DXM (0.014 mg/kg/day), or their combination, respectively, and further received PHZ (60 mg/kg/day) intervention on day 4 and 5 only. Treatments lasted for 7 days. Phenylhydrazine toxicity manifested as lowered haemoglobin, white blood cells, lymphocytes, red blood cells, and platelet levels by 45.86%, 53.47%, 75.69%, 46.89%, and 30.29%, respectively, in rats. This was accompanied by an increase in serum alanine (ALT; 108.25%) and aspartate (AST; 78.79%) aminotransferases, urea (84.36%), total cholesterol (81.55%), and triglycerides (123.42%) levels. Similarly, malondialdehyde levels and serum cyclooxygenase-2 activity were elevated ( < 0.05) in the rats liver and spleen, respectively. Just HEASR alone, or in combination with DXM, preserved haematological and biochemical parameters, cyclooxygenase-2 activity, and corticosterone levels during PHZ intoxication and restored renal histopathological alterations in rats. The HEASR was found to contain high flavonoid and phenolic phytochemicals and demonstrated better in vitro antioxidants inhibitory action.