Tyrosine is a non-essential amino acid meaning that it is produced naturally within the body. Tyrosine plays an important role in the production of neurotransmitters including dopamine and norepinephrine. These neurotransmitters play important roles surrounding minimizing stress and brain function and are one reason as to why this amino acid is so important for mood and stress levels. Tyrosine helps with mental alertness, anxiety, activity as well as the activity of some hormones, the most important being thyroid hormone. Low thyroid levels can result in symptoms including increased feelings of fatigue, depression, anxiety and decreased libido.