Phenylalanine is an essential amino acid that is important for the synthesis of proteins in the body. It is also a precursor for several important neurotransmitters, including dopamine, norepinephrine, and epinephrine. It is found in many protein-rich foods, such as meats, dairy products, and soy products.L-Phenylalanine is also available as a dietary supplement for those who may not get enough from their diet. It is commonly used to improve mood and cognitive function, and may also have potential benefits for those with depression, chronic pain, and skin conditions.