L-Tyrosine, also called 4-hydroxyphenylalanine, is an amino acid (or protein building block) which is manufactured within animal and plants cells alike. It's most important function in the human body is its utilization by cells in the brain which convert it to neurotransmitters.

Neurotransmitters are essentially the chemical messengers within our brains which relay information between neurons and other cells. Some of these neurotransmitters, which are converted from l-tyrosine, include norepinephrine (noradrenaline), epinephrine (adrenaline), and dopamine (which effects cognition and behavior). These neurotransmitters play an important role in mood, stress reactions, and alertness.

Those lacking sufficient amounts of l-tyrosine often have mood disorders, such as depression, and may benefit from added amounts of l-tyrosine in their deits. Foods such as dairy products, chicken and meats, nuts, and grains. Additional supplements may also enhance mental cognition and bring forth better moods. Supplements, such as bulk l-tyrosine powder may be added to one's diet.

Individuals suffering from conditions such as Parkinson's disease and Alzheimer's may also be positively effected by a subtle increase of l-tyrosine due to its effects on stress hormones; however, one should speak to their physician about such plans before supplementing l-tyrosine themselves.