Dual-Strain Psychobiotics Combining Live Lactiplantibacillus plantarum PS128 and Heat-Treated Lacticaseibacillus paracasei PS23 Improve Psychological and Neuroendocrine Outcomes in Stressed Adults: A Randomized, Placebo-Controlled Trial

Chronic psychological stress impairs neuroendocrine balance and increases the risk of mental health disturbances, including anxiety, sleep disruption, and low mood. The gut–brain axis has emerged as a promising target for stress modulation, particularly through psychobiotic interventions. This randomized, double-blind, placebo-controlled trial evaluated the effects of a combined psychobiotic formulation (Neuralli Mood), comprising live Lactiplantibacillus plantarum PS128 (PS128) and heat-treated Lacticaseibacillus paracasei PS23 (HT-PS23), on the psychological and physiological stress responses in a high-stress occupational population. A total of 116 healthy participants with elevated perceived stress (PSS ≥ 14), primarily firefighters, were randomly assigned to receive the dual-strain supplement or placebo for 8 weeks. Stress-related outcomes were assessed by using validated psychological scales and serum biomarkers. Compared with placebo, the psychobiotics group showed significantly greater reductions in overall job stress perception (JSS), state anxiety (STAI), and insomnia severity (ISI) (all p < 0.05). Additionally, serum adrenocorticotropic hormone (ACTH) and norepinephrine levels were significantly reduced post-intervention, whereas cortisol levels remained unchanged. These findings suggested that combining live and heat-treated psychobiotic strains may provide a safe and effective strategy for alleviating psychological stress and regulating neuroendocrine function in high-risk populations.