Tyrosine is an amino acid which can be converted in the body into
phenylalanine. Among other things, phenylalanine is converted into
l-DOPA, which is the major source of dopamine for the brain. Were it not
the case that both tyrosine and phenylalanine were available in the diet,
taking tyrosine pills might make sense.
Even if there is no benefit to taking tyrosine, there is
probably no harm, unless as was the case of tryptophan another AA
involved in another transmitter (serotonin), the tablets are contaminated
with toxic substances. A more direct way of increasing the amount of
dopamine would be to take dopamine tablets, but dopamine does not get
inside the brain where it is needed. DOPA is an amino acid which
gets into the brain cells which can use it to manufacture dopamine.
Unfortunately this population of cells capable of manufacturing dopamine
gets smaller and smaller with the progression of PD, and so DOPA, specifically
one form of DOPA (l-DOPA) has progressively less effect. Tyrosine will not
compensate for the loss of response to l-DOPA since its theoretical effect
is to increase the l-DOPA.
The bottom line is, except for the placebo effect, tyrosine is unlikely
to help; except for possible contamination, it is unlikely to do harm.
I am glad I was able to provide you with this simple explanation.
Best wishes, Allan (dx 1990)
