2. L-Tyrosine – How Does It Work?
Tyrosine is involved in the production of catecholamines, also known as the neurotransmitters dopamine, noradrenaline and adrenaline which are responsible for the “fight or flight” response. Tyrosine gets broken down by the body in two stages.
First, it needs to be synthesized into L-DOPA (a precursor of dopamine and a common nootropic that has benefits similar to those of Tyrosine), before being converted by enzymes and replenishing one of the three catecholamines.
For L-Tyrosine to have a beneficial impact on our cognitive function, the cognitive tasks must first be challenging enough to deplete our neurotransmitter stores in the first place. 
When presented with cognitively demanding tasks, studies on cold stress and sleep deprivation have shown that L-Tyrosine acts as a buffer that prolongs the anti-stress effects of noradrenaline by delaying its depletion. This, in fact, is also the most prominent characteristic of L-Tyrosine.
When we expose our bodies to uncontrollable acute stress, the concentrations of norepinephrine usually take a dip, resulting in unwanted reduced motor control and in some cases, unwanted aggression. Among others, a recent study on military cadets has proven Tyrosine to be an effective stress reliever, as it had a profound effect on the mood of the individuals during a week-long intense combat training course. 
L-Tyrosine is also a common pharmaceutical solution for individuals suffering from dementia. Catecholamine levels with such individuals are usually decreased, so on the basis of its catecholamine producing properties, supplementation with Tyrosine proves to be a good neuroprotective agent.
Tyrosine, in isolation, will not necessarily give you a mental boost. It will prove beneficial if you find yourself in situations where your natural catecholamines will be depleted by providing more material (Tyrosine) to make catecholamines from.