DDC and Parkinson disease: Catechol-o-methyl transferase (COMT) inhibitors, anticholinergics, monoaminoxidase inhibitors and dopamine agonists are all additional PD drugs that can be administered with or without L-dopa (Weis et al., 2019), and they can impact the abundance of gut microbial dopa decarboxylases, thus influencing dopamine metabolism (van Kessel et al., 2019).