Aims: To confirm the stress-relieving effects of heat-inactivated, enteric-colonizing Lactobacillus gasseri CP2305 (paraprobiotic CP2305) in medical students taking a cadaver dissection course. Methods and Results: Healthy students (21 males and 11 females) took paraprobiotic CP2305 daily for 5 weeks during a cadaver dissection course. The General Health Questionnaire and the Pittsburgh Sleep Quality Index were employed to assess stress-related somatic symptoms and sleep quality respectively. The aggravation of stress-associated somatic symptoms was observed in female students (P = 0.029). Sleep quality was improved in the paraprobiotic CP2305 group (P = 0.038), particularly in men (P = 0.004). Among men, paraprobiotic CP2305 shortened sleep latency (P = 0.035) and increased sleep duration (P = 0.048). Diarrhoea-like symptoms were also effectively controlled with CP2305 (P = 0.005) in men. Thus, we observed sex-related differences in the effects of paraprobiotic CP2305. In addition, CP2305 affected the growth of faecal Bacteroides vulgatus and Dorea longicatena, which are involved in intestinal inflammation. Conclusions: CP2305 is a potential paraprobiotic that regulates stress responses, and its beneficial effects may depend on specific cell component(s). Significance and Impact of the Study: This study characterizes the effects of a stress-relieving para-psychobiotic in humans.