DOPA Decarboxylase (DDC) is an enzyme responsible for the synthesis of the neurotransmitter dopamine, which is performed metabolizing levodopa by decarboxylation reaction. It has being active in several clinic disorders, including Parkinson’s disease. Carbidopa (CDOPA) is a peripheral inhibitor of DDC that is ingested together with the levodopa, being the antiparkinsonian drug most used nowadays. Aiming to give a quantum chemistry theoretical description of the carbidopa molecule, we present here its geometrical, optoelectronic, and vibrational spectroscopic results. Annealing calculations were employed to explore the space of the molecular geometry of carbidopa, in order to obtain its most stable conformations of smaller energies by using density functional theory (DFT) with the LDA/PWC, GGA/PBE, and GGA/BLYP functionals. The carbidopa’s structural data (bond length, bend, and torsion angle), charge population analysis (absorption spectra), and molecular orbital study (HOMO, LUMO, PDOS, and DOS) are then obtained considering one of its smallest conformation energy. Furthermore, a detailed interpretation of the carbidopa harmonic vibrational frequencies are here also presented, through the analysis of its infrared (IR) and Raman scattering spectroscopy.