Tyrosine

Tyrosine, an amino acid, is a precursor to dopa, which is converted to the neurotransmitters dopamine, noradrenaline (norepinephrine) and adrenaline (epinephrine). Tyrosine is converted to l-dopa by the enzyme tyrosine hydroxylase. Dopamine is important for both pleasesure and motivation, and both noradrenaline and adrenaline have a key role in the fight or flight response of the sympathetic nervous system, which is activated by emotional or physical arousal.

It is also a precursor to the thyroid hormones triiodothyronine (T3) and thyroxine (T4)

Tyrosine and its precursor phenylalanine are required for the synthesis of coenzyme Q10. People with the genetic condition phenylketonuria (PKU) need tyrosine supplements because they are unable to phenylalanine.

ME/CFS
Reduced levels of plasma tyrosine have been found in ME/CFS patients.

Evidence
Two studies of healthy adults have found that tyrosine supplements moderately increased cognitive performance and mental status after prolonged periods of without sleep and intensive military training.