QUOTE(kaleshnikov @ May 07, 2012, 03:00 AM)
You won't derive much of a cognitive benefit from Thyrosine as the dopamine that does get created will not cross the blood/brain barrier, but it will linger around in other dopamine receptors through out your body. Basically, you increase your chances of all the shitty side effects of Adderall/Ritalin, without getting much of the cognitive benefit.
Dopamine does not cross the BBB, but both L-tyrosine and L-Dopa DO cross the BBB. Likewise, most tyrosine that is ingested will not be converted into dopamine within the blood, but instead will be taken up into cells to be used for general protein synthesis (note: only a portion of tyrosine that passes through the BBB will be used in the dopamine synthesis pathway). SOME of the l-tyrosine within the blood will undergo hydroxylation to become L-DOPA, then L-DOPA can undergo decarboxylation to become dopamine, but this process takes time and significant amounts of tyrosine and L-DOPA make it into the CNS. The small amount of dopamine formed from LOW DOSE tyrosine (under 1 gram) in the peripheral circulation cause little to no side effects. Another portion of the supplemented tyrosine will act as a building block for the production of thyroxine, which could cause worsening of hyperthyroidism or Grave's Disease if already present.
Further, the way that tyrosine acts in supporting dopamine production is HUGELY different than the mechanism of action of the dopamine/noradrenaline re-uptake inhibitors (Ritalin/Adderall). The production of dopamine from tyrosine in the CNS occurs on an "as needed" basis (i.e. synaptic dopamine levels will not be largely increased in the synapse unless a task is mentally or physically demanding and requires higher release of dopamine).
So in summary:
Does some tyrosine get converted into dopamine in the blood? Yes
Is it significant enough to cause similar side effects to Ritalin? Not really
Does tyrosine raise CNS levels of dopamine when needed? Yes
Does it benefit cognition if a higher level of dopamine is required? Yes
All this being said, if the first poster is looking for something as a study aid, then tyrosine can help them out when mentally stressed. If on the other hand the poster has full blown ADHD (which is completely different than just wanting a dopamine boost), then they should talk to their doctor about getting medications specifically for the ADHD.