An L-Tyrosine is a form of amino acid that is not generally required to be healthy. A Tyrosine (or L-Tyrosine) supplement is a supplement to increase alertness and mental arousal. They help you respond and increase your over-all alertness level which helps to increase your focus. However, there are side-effects. Some side-effects include: restlessness, insomnia, anxiety, and heart palpitations.