Amino acids are classified as either essential or non-essential. Essential amino acids cannot be synthesised in the body and must be obtained from the diet, whereas non-essential amino acids, whilst still essential for health, can be synthesised in the body and are therefore not classified as 'essential'. Phenylalaine is an essential amino acid and is the precursor for the amino acid tyrosine. Like tyrosine, it is the precursor for the neurotransmitters called catecholamines (adrenaline, noradrenaline and dopamine). As with all our amino acids, Lamberts L-Phenylalanine is presented in its free-form for maximum absorption. Each capsule provides a full 500mg of L-Phenylalanine. 1 capsule daily with water or fruit juice. An Amino Acid is best taken half an hour before any meal or at bedtime. Caution: Not to be taken by phenylketonuria sufferers (PKU). Not to be used with MAO inhibitors (a type of anti-depressant medicine). Do not take if pregnant or breast feeding.