Just thought I'd add my own word of caution about Tyrosine. I also read in a number of places that you shouldn't take Tyrosine together with l-dopa meds. From what I understood, this is because they compete with each other for absorption by our brains, and so, by taking them together we would render one of them (or both) less effective. I didn't read anything about combining them being dangerous (but this isn't a guarantee that it isn't, of course).
On the more positive side I did find a couple of old studies that speak for the virtues of Tyrosine for PD: One (from 1982)concludes that "l-tyrosine administration can increase dopamine turnover in patients with disorders in which physicians wish to enhance dopaminergic neurotransmission" (http://www.ncbi.nlm.nih.gov/pubmed/6175872
). The other (from 1989) concludes that "For some patients, 3 years of L-tyrosine treatment was followed by better clinical results and many fewer side effects than with L-DOPA or dopamine agonists." (http://www.ncbi.nlm.nih.gov/pubmed/2502304
However these studies are 20-30 years old, which makes me wonder that if Tyrosine was so great why isn't everobody using it today? And also the 1989 study only involved a tiny number of PD patients. So, wondering if anyone has any more info that could shed some light in this (e.g., any more recent studies?).
Turnip: Your point that there is a mechanism that limits the maximum amount of tyrosine that can converted to levadopa seems totally true and maybe is the real reason why L-dopa is today the medication of choice... but on the other hand, I'm tempted to speculate that precisely that aspect could make Tyrosine have some beneficial long-term advantages. Intuitively, I quite like the idea that there's a mechanism that prevents my neurons from overworking too much and thus protect them from any possible situation of "neuron burn-out" we might inadvertently induce by taking meds that get them to work harder to create more dopamine. I know this line of thinking is pure speculation from my side, as I've never seen this notion of "neuron burn-out" discussed or addressed anywhere, but I confess it does cross my mind, and so would be interested to know any view you (or any others) may have on it.
Cheers to all,