Gut microbiota influences the clinical response of a wide variety of orally administered drugs. However, the underlying mechanisms by which drug-microbiota interactions occur are still obscure. Previously, we reported that tyrosine decarboxylating (TDC) bacteria may restrict the levels of levodopa reaching the circulation in patients with Parkinson's disease (PD). We observed a significant positive association between disease duration and the abundance of the bacterial tdc-gene. The question arises whether increased exposure to anti-PD medication could affect the abundance of bacterial TDC, to ultimately impact drug efficacy. To this end, we investigated the potential association between anti-PD drug exposure and bacterial tdc-gene abundance over a time period of two years in a longitudinal cohort of PD patients and healthy controls. Our data reveal significant associations between tdc-gene abundance, anti-PD medication, and gastrointestinal symptoms and warrants further research on the effect of anti-PD medication on microbial changes and gastrointestinal-function.