Since L-Dopa, the widely used drug in Parkinson's disease treatment, is decarboxylated by aromatic L-amino acid decarboxylase (AADC), which is found in both dopaminergic and serotonergic neurons, it is possible for serotonergic neurons to convert L-Dopa into dopamine and generate excessive neuronal death by creating reactive oxygen species and quinoproteins. The association of serotonin with mood and cognition may explain some of the side-effects observed in patients treated with L-Dopa due to serotonin deficit.[9][10]