 As this benefit is presumed to be a central effect, the addition of carbidopa, a peripheral DOPA decarboxylase DDC inhibitor, may favorably impact the drugs treatment profile. Carbidopa is utilized as a blocker of peripheral DDC, an enzyme required for the conversion of droxidopa into norepinephrine. Therefore, inhibition of peripheral DDC should result in a reduction of any side effects resulting from the peripheral production of norepinephrine, whilst allowing for increased central levels, and hence, increased centrally mediated benefits. 