Tyrosine is an amino acid typically found in cheeses and meats. L-tyrosine ultimately is used to increase levels of circulating dopamine in the brain. L-tyrosine is not a direct precursor to dopamine; it is first converted into L-DOPA in the brain which is then directly used for dopamine synthesis as well as norepinerphrine and epinephrine (adrenaline) if needed. These three catecholamines are important neurotransmitters which play a large role in the regulation of attention, memory, cognition, and mood.
When l-tyrosine is supplemented it is converted into L-DOPA by an enzyme called tyrosine hydroxylase, which is responsible for the regulation of dopamine synthesis1https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065393. This process of converting l-tyrosine into L-DOPA is rate limited by the enzyme, which means that it will only convert as much tyrosine as needed, and acts sort of as a “safety” net to prevent it being oversatured.
In short, l-tyrosine is best used to keep your dopamine levels at their baseline and delaying the depletion of dopamine, which would be helpful when doing something like studying which no doubt depletes them. However l-tyrosine will not elevate dopamine levels beyond their normal threshold.
L-DOPA can also be supplemented on its own but there is no rate-limited conversion into dopamine in the brain1https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065393. This can lead to abnormally elevated dopamine levels in the brain. I do not recommend taking L-DOPA for this reason as it can lead to a downregulation of dopamine over time. When you saturate your brain with abnormally high levels of any neurotransmitter the body responds by decreasing the density of dopamine receptors thereby decreasing the ability of your brain to absorb dopamine in the future.
This is true with any drug that elevates neurotransmitters to unusually high levels, the brain always tries to maintain homeostasis, which means it is aiming to achieve a neurochemical equilibrium. If you start chronically elevating certain neurotransmitters it is going to respond by decreasing the ability of the brain to absorb these neurotransmitters.
For these reasons I do not recommend taking L-DOPA. L-tyrosine is much safer and poses none of the risks that L-DOPA has.
Where to Purchase Tyrosine
Tyrosine may be purchased at Nootropics Depot.
I recommend Nootropics Depot because they have been around for a long time and have maintained a solid reputation. They have excellent quality control metrics: they do in-house testing as well as independent 3rd-party testing, and they have certificates of analysis available for all of their products.
The recommended dosages are 100-150 mg/kg of bodyweight, which ranges from 7-10g for a 150lb person and 9-13.5g for a 200lb person.