This is info on tyrosine from Dr Jocker's article - 10 Nutrients to Improve Thyroid Function...
7. Tyrosine:
The amino acid tyrosine works in a joint effort with iodine to produce thyroid hormones T4 and T3. Tyrosine provides the structural foundation for thyroid hormones. Low levels of tyrosine levels is linked to a reduction in thyroid hormones and also a decrease in neurotransmitters like dopamine affecting the central nervous system (12).
Under conditions of high stress, the loss of available tyrosine to the brain results in one’s loss of interest, slower movement and a decline in physical health. Low tyrosine levels coupled with chronic stress leads to a decrease in enzymatic activity responsible for producing hormones. These influences affect the hypothalamus and adrenal glands which adversely leads to the dysfunction of the thyroid.
Increasing tyrosine in clinical studies in patients with low thyroid hormones whom also exhibited signs of depression, fatigue and lowered immunity had improved stress levels, neurological function, and higher levels of circulating thyroid hormones. (13)"