Clostridium butyricum is a probiotic bacterium that has gained attention for its potential to mitigate side effects of chemotherapy, particularly gastrointestinal toxicity such as diarrhea and mucositis. The scientific evidence supporting its use comes primarily from preclinical studies and a limited number of clinical trials, mostly conducted in East Asia. These studies suggest that C. butyricum supplementation can help restore gut microbiota balance disrupted by chemotherapy, enhance the production of beneficial short-chain fatty acids (such as butyrate), and reduce inflammation in the gut lining. Butyrate, in particular, is known to promote mucosal healing and strengthen the intestinal barrier.

Several small randomized controlled trials in patients undergoing chemotherapy for colorectal cancer or hematologic malignancies have reported that C. butyricum supplementation can reduce the incidence and severity of diarrhea, improve patient quality of life, and sometimes shorten hospital stays. Mechanistically, these benefits are thought to arise from both direct anti-inflammatory effects and the restoration of a healthy microbial community. However, most of the available clinical studies are small, and larger, high-quality trials are lacking. There is no longstanding traditional use of C. butyricum for chemotherapy side effect management, as its application in this context is recent and based on modern probiotic science. Overall, while the preliminary data are promising and justify cautious optimism, the strength of evidence is still moderate (rated 3/5), pending confirmation in larger and more diverse patient populations.