The term "non-essential" may be misleading. Although histidine was once considered an essential amino acid for infants only, subsequent research has determined that histidine may also be essential for adults. Arginine, ornithine, cysteine, cystine, taurine and tyrosine are classified as non-essential amino acids but may be essential for individuals with certain diseases or nutritional concerns. A suboptimal intake of the essential amino acids increases the body's need for the non-essential amino acids. Solgar Amino Acids are of the highest quality available.