Capsaicin (CAP) is an active ingredient in chili peppers with a variety of pharmacological activities and potential effects on psychiatric disorders.95–97 CAP was found to improve depression and serum levels of 5-hydroxytryptamine (5-HT) and tumor necrosis factor-α (TNF-α) in mice with lipopolysaccharide (LPS)-induced depressive-like behavior and to significantly upregulate the relative abundance of key microbes such as Oscillospira. Here, TNF is linked to depressive symptom measurement.