Amino acids are the building blocks of body proteins, including structural and contractile proteins, enzymes, and certain hormones and neurotransmitters. They also function in many other metabolic activities, are used as substrates for energy production, are involved in immune function, ammonia detoxification, the synthesis of nucleic acids, and also function as antioxidants. Amino acids, either free form or in the form of small peptides, are potent physiological and pharmacological agents.