Carbidopa (Lodosyn) is a drug given to people with Parkinson's disease in order to inhibit peripheral metabolism of levodopa.

Therefore, the PD brain, which is deficient in dopamine, will not receive as much of its prodrug precursor levodopa/L-DOPA due to peripheral DDC breakdown.

Carbidopa, an inhibitor of aromatic amino acid decarboxylation, is a white, crystalline compound, slightly soluble in water, with a molecular weight of 244.3.

This results in the newly formed dopamine being unable to cross the blood–brain barrier and the effectiveness of L-DOPA treatments is greatly decreased.

This is extremely useful in the treatment of Parkinsons disease symptoms because the amount of levodopa administered to the patient can be greatly reduced.

Carbidopa is also used in combination with 5-hydroxytryptophan (5-HTP), a naturally occurring amino acid which is a precursor to the neurotransmitter serotonin and an intermediate in tryptophan metabolism.

[citation needed] The synthesis begins with a modified Strecker reaction using hydrazine and potassium cyanide on arylacetone (1) to give 2.

More vigorous hydrolysis with 48% HBr cleaves the amide bond and the aryl ether group to produce carbidopa (4).