The effect of carbidopa and benserazide on human plasma 5-hydroxytryptophan levels

Peripheral aromatic amino acid decarboxylase inhibitors increase human plasma 5-hydroxytryptophan (5-HTP) levels. However the 5-HTP, which is synthesized in the intestine, is not present in a sufficient quantity to influence brain 5-HT to any significant degree. Thus, peripheral decarboxylase inhibitors are unlikely to affect brain 5-HT function via 5-HTP which is synthesized peripherally.