COMT and Parkinson disease: SCFAs‐producing bacteria may reduce or increase outside of an “optimal range.” Considering that Bifidobacterium, Lactobacillus, and Akkermansia are beneficial for human health, the increased Bifidobacterium and Lactobacillus may be associated with PD medications, especially COMT inhibitors, while a high level of Akkermansia may be associated with aging.