In
http://www.dcnutrition.com/AminoAcid...cordNumber=129
it states that tyrosine can be used as an adjunct in the treatment of PD.
it says metabolism of tyrosine necessitates large doses compared to L-Dopa. Also, its effectiveness is increased when combined with Sinemet.
This may be why I did not see much improvement of symptoms when I tried it some years ago. I did not take it together with Sinemet, and did not know high doses are needed due to its fast metabolism.
I read somewhere that tyrosine can not be sythesised in the brain, which is presumably why the above paper describes it as a nutriant.
It is synthesised in the body and readily passes the BBB to be made into L-dopa, dopamine and adrenalin.
Ron