Carbidopa is a reversible competitive inhibitor of aromatic L-amino acid decarboxylase (also known as dopa-decarboxylase) that cannot cross the blood brain barrier. It has been used successfully for many years to block the extracerebral synthesis of dopamine and avoid nausea and vomiting in patients with Parkinson's disease taking levodopa. The investigators reasoned that carbidopa could have a similar antiemetic effect in patients with FD.