Tyrosine is classified as a non-essential amino acid since it can be synthesised from phenylalanine, there are special considerations that may make it a conditionally-essential amino acid. That's because while a man can synthesise most of the non-essential amino acids from glucose and ammonia, tyrosine synthesis requires the availability of phenylalanine, just as cysteine requires the availability of methionine.
Tyrosine seems to have become one of the new darlings of the supplement world. The reason seems to be mainly because it is the precursor to some neurotransmitters such as norepinephrine and dopamine and it has been shown that that tyrosine administration can accelerate catecholamine synthesis in the human sympathoadrenal system.
The latest information on tyrosine contains claims that the use of tyrosine will do wonders for sports performance and weight loss, and for anything else that may ail you.