the RDA of B6, because doing so would act to neutralize
oral L-DOPA too quickly. These days, almost all Parkinson's
patients on L-DOPA take the drug in a combination with an
artificial decarboxylase inhibitor, called Carbidopa (the
combination is called Sinemet). But even with Carbidopa,
Parkinson's patients are advised not to exceed a daily dose of B6
of 25 mg, since more will overwhelm the Carbidopa effect, and
cause pharmacologic L-DOPA to be destroyed in the liver before it
can get into the brain.
Now, Carbidopa, because it acts on the same metabolizing
enzyme in the liver, performs exactly the same preservative
service for 5-HTP as for L-DOPA."