T Nation

Tyrosine and Thyroid


I have some sub-clinical hypothyroidism, as evidenced by my TSH blood work and morning/afternoon body temperature. I was under the impression that supplementing with tyrosine (as in Brain Candy for example) is important for one's thyroid as it combines with iodine to make T4.

However, I just came across an article which basically says that since tyrosine is a precursor to dopamine, which turns into the flight or fight hormones epinephrine/norepinephrine, it can suppress thyroid function.

Could the same then be said for something like caffeine, which also stimulates the adrenal hormones?


I have never encountered the theory of tyrosine inhibiting the thyroid in any scientific literature.

I did find it now Googling popular sites.

Rather ironically, the sites I found being their argument by criticizing claims that tyrosine will aid thyroid production by stating (correctly) that there’s no study supporting that. They then follow that with their unsupported theory that tyrosine impairs thyroid function, this time however having no care about lack of evidence.

It is true that you don’t want to overstimulate epinephrine production. It’s possible to overstimulate with caffeine. For all things there’s such a thing as too much use or overly-frequent use.