Benefits
Anxiety scores during months of exam preparation
In 60 medical students preparing for a national exam, 10 billion heat-killed cells a day for 24 weeks lowered trait anxiety and a hospital anxiety score versus placebo. State anxiety, an overall health questionnaire and salivary cortisol did not differ, and results were not corrected for the many outcomes tested. The maker funded the trial.
Sleep quality ratings under ongoing stress
In two placebo-controlled trials in students under stress, a 5-week drink and 24-week tablets improved scores on a standard sleep questionnaire; in the shorter trial the gain was seen in men only. A pooled analysis of six trials, which Europe PMC lists as funded by Asahi, found scores 0.77 points better than control.
Sleep stage timing on home EEG recordings
In the 24-week tablet trial, a single-channel home EEG showed a shorter time to reach deep sleep, less time awake after first falling asleep and a larger share of deep-sleep brain waves in the first cycle versus placebo. Total deep sleep, REM sleep and overall deep-sleep wave power did not differ. These were secondary measures in one maker-funded trial.
Mental stress ratings after a single dose
In a crossover trial of 28 healthy adults, one 10 billion-cell dose before demanding mental tasks led to larger drops in self-rated mental stress and tension-anxiety than placebo over the next hour. These were secondary measures, the main one being a brain wave marker; the other mood scales did not differ, and maker employees ran the study.
Low mood scores on questionnaires during exam stress
In the 24-week trial of students preparing for a national exam, 10 billion heat-killed cells a day lowered a hospital depression score and the depression part of a general health questionnaire versus placebo, with no correction for the many outcomes tested; the questionnaire total did not differ. Scores stayed in the normal range, and a depression scale did not differ in the single-dose study.
Bowel movement frequency in adults with irregular habits
In 118 adults with infrequent or very frequent bowel movements, a daily drink with 10 billion heat-killed cells for 3 weeks increased bowel movement counts and improved stool odor versus placebo, but stool form, the outcome the study was sized on, did not differ, and the group included both habits. Bowel frequency did not differ in the 24-week tablet trial.
Mild menopausal symptom scores in women in their 40s and 50s
In women aged 40 to 60 with mild symptoms and regular cycles, tablets of 10 billion heat-killed cells a day for six cycles lowered two menopausal symptom questionnaire totals, including hot flash and mood items, versus placebo. The share of women who improved was not significantly different, 19 randomized women were excluded after the fact, and all authors work for the maker.
Mechanism of action
Non-living cell parts acting on the gut lining
Because the cells are heat-killed, any effect has to come from the cell bodies and their surface components rather than from bacteria growing in the gut, which is what places CP2305 under the postbiotic definition. Which component matters has not been identified.
Gut-brain signaling and the autonomic nervous system
In two maker-run human trials, heart rate variability shifted toward parasympathetic (rest and digest) activity versus placebo, and a single dose raised EEG alpha power at some scalp sites. These are physiological markers, not outcomes, and the proposed vagus nerve route is based on unpublished rat work cited by the researchers.
Effects on colon nerve activity and stress-related diarrhea in rats
In rat colon tissue, live and non-living CP2305 cells both damped nerve-driven fluid secretion, and both eased diarrhea triggered by a stress hormone in rats. This is animal and tissue work only and has not been measured in people.
Brain growth factor genes in stressed mice
In mice exposed to repeated social stress, a diet with heat-inactivated CP2305 restored food intake and raised hippocampal gene expression of BDNF and related nerve growth factors. Gene expression in mouse brain tissue does not show what happens in the human brain.
Clinical trials
Randomized, double-blind, placebo-controlled parallel trial (UMIN000027303) of two tablets a day giving 10 billion heat-inactivated, washed CP2305 cells versus identical tablets with dextrin; the planned primary outcomes were questionnaire scores and salivary cortisol and chromogranin A, with sleep EEG and gut bacteria secondary; funded by Asahi Group Holdings, one author an Asahi employee (Nishida et al. 2019, Nutrients)
60 healthy Japanese sixth-year medical students (41 men, 19 women) preparing for the national licensing exam.
Versus placebo, trait anxiety (STAI), the PSQI sleep score, HADS anxiety and depression and irritability ratings improved, while state anxiety, the GHQ-28 total and salivary cortisol did not differ; salivary chromogranin A was lower. On EEG, time to first deep sleep and wake time after sleep onset fell and the first-cycle delta ratio rose; total REM, deep sleep and delta power did not differ. Bowel frequency and stool form did not differ. No adverse events, and no correction for multiple comparisons.
Randomized, double-blind, placebo-controlled parallel trial of a daily fermented-milk-based drink with 10 billion heat-inactivated CP2305 cells versus an acidified milk drink without bacteria; no primary outcome named; two authors are Asahi Group Holdings staff (Nishida et al. 2017, J Appl Microbiol)
32 healthy medical students (21 men, 11 women), 16 per group, during a cadaver dissection course.
The PSQI sleep score improved versus placebo (P = 0.038), driven by men (P = 0.004), with no difference in women; men also had shorter sleep latency and longer sleep. Diarrhea-like symptoms eased in men only. The GHQ-28 total, STAI and HADS anxiety scores and salivary stress markers did not differ between groups.
Randomized, double-blind, placebo-controlled crossover trial (UMIN000056164) of one dose of tablets with 10 billion heat-treated CP2305 cells before mental arithmetic and listening tasks, with change in EEG alpha power as the stated primary outcome and heart rate variability and stress and mood questionnaires as other measures over 60 minutes; funded by Asahi Group Holdings, all four authors employees of Asahi Quality and Innovations (Tanihiro et al. 2026, Front Nutr)
28 healthy Japanese adults aged 20 to 44.
Alpha power rose more than with placebo at 4 of 8 electrode sites, and RMSSD, a parasympathetic index, rose more. Mental stress ratings (P = 0.015) and POMS2 tension-anxiety improved more than with placebo; anger, confusion, depression, fatigue, vigor and friendliness scales did not differ. The authors note that tension-anxiety did not rise under placebo after the tasks, and EEG and heart rate analyses dropped some participants for data quality. No adverse events.
Randomized, double-blind, placebo-controlled parallel trial of a daily 200 mL drink with 10 billion washed, heat-treated CP2305 cells versus the same drink without them; the sample size was based on stool form; funded by Asahi Group Holdings, six of eight authors its employees (Sugawara et al. 2016, Microb Ecol Health Dis)
120 healthy adults (118 completed) who had 4 or fewer, or 10 or more, bowel movements a week.
Bowel movement counts (p = 0.035) and fecal odor scores (p = 0.040) improved versus placebo, while objectively rated stool form, the outcome the sample size was based on, did not differ significantly; the paper's text reports the count gain as significant in the subgroup with hard stools (p = 0.019). Fecal p-cresol fell, Bifidobacterium rose and Clostridium cluster IV fell versus placebo. Because the group combined people with too few and too many bowel movements, the direction of benefit for each person is not clear from the overall count.
Randomized, double-blind, placebo-controlled parallel trial (UMIN000039086) of two tablets a day with 10 billion heat-inactivated CP2305 cells for six menstrual cycles; primary outcome symptom questionnaire scores; funded by Asahi Quality and Innovations, all four authors its employees (Sawada et al. 2022, Nutrients)
Women aged 40 to 60 with regular cycles and mild symptoms; 102 randomized, 80 analyzed.
Simplified Menopausal Index total, vasomotor and psychological scores and Greene Climacteric Scale total, somatic and vasomotor scores improved more than with placebo. The share of women improving on the index total was 75.0% versus 55.0% (p = 0.059), and on the Greene scale total 52.5% versus 40.0% (p = 0.262); neither difference was significant. Nineteen women were excluded after randomization, mostly for cycle irregularities. No adverse events.
Randomized, double-blind, placebo-controlled parallel safety trial (UMIN000021511) of 20 tablets a day giving 100 billion heat-inactivated CP2305 cells, ten times the recommended daily intake; sponsored by Asahi, four of six authors Asahi employees (Fuchida et al. 2026, Toxicol Rep)
44 healthy Japanese adults, including some prone to constipation; 43 analyzed.
No safety concerns in physical examinations, blood counts, blood chemistry or urinalysis. Subjective symptoms numbered 29 mild events in 6 people on CP2305 and 14 in 5 on placebo, none judged related to the tablets. This was a safety study and did not test benefits.