eng Oriental Scientific Publishing Company Biosciences Biotechnology Research Asia 0973-1245 2026-03-30 23 1 305 317 10.13005/bbra/3499 58286 article Indu Ghooli 1 Archana Jorige 1 Tejasri Talloju 1 Department of Pharmacology, R.B.V.R.R. Women’s College of Pharmacy (Affiliated Osmania University), Hyderabad, India Stress, particularly chronic stress, affects physical and mental health and causes adverse outcomes. Mental disorders account for 14% of all diseases, with depression being the main cause. Chronic Unpredictable Stress (CUS) models are used to study stress-induced disorders and evaluate therapeutic agents. Vitamin D3(Vit D₃), essential for mood regulation and neuroplasticity, L-theanine, an amino acid in tea with anxiolytic and neuroprotective qualities, have been connected to depression and stress susceptibility. This study used adult male Albino Wistar rats aged ten–fifteen-weeks weighing 250–350 g to investigate the combined effects of L-theanine and Vit D₃in the CUS Model. This involves administering Vit D₃ and L-theanine to rodents after exposure to random stressors for a predetermined duration. Behavioural tests including forced swim test(FST), sucrose preference test(SPT), open field test(OFT), splash test, and novel object recognition test(NORT) evaluated cognitive and anhedonia symptoms resembling depression. Biochemical assays measured glucose, total cholesterol, triglyceride, and cortisol levels in serum, and adrenal gland relative weight was measured. Results indicated that L-theanine and Vit D3 significantly mitigated CUS-induced behavioural changes, showing reduced immobility in forced swim test, increased exploratory behaviour in OFT, normalized SPT and increased cognition in NORT. Biochemical assessment showed triglycerides, cholesterol, glucose, and cortisol levels were lower in treatment groups than stress control group. The results demonstrate that co-administration of L-theanine and Vit D₃confers superior protection against CUS-induced behavioural and neurochemical deficits compared with monotherapy, indicating a synergistic therapeutic interaction. This finding supports the potential of combination strategies in stress-related mood disorders. Further research is required to define the molecular pathways mediating this enhanced effect. https://www.biotech-asia.org/vol23no1/vitamin-d%e2%82%83-and-l-theanine-co-therapy-alleviates-behavioral-and-biochemical-deficits-in-a-chronic-unpredictable-stress-rodent-model/ Behavioural assessments; Biochemical deficits; Chronic unpredictable stress (CUS); Cortisol; L - Theanine; Vitamin D3