HealthWise® L-Phenylalanine is 100% pure pharmaceutical grade amino acid powder. Phenylalanine is an essential amino acid which is highly concentrated in the human brain and plasma. Phenylalanine is a precursor for tyrosine and these two amino acids are used by the brain to manufacture neurotransmitters. The great uplifter! Did you know? Tofu and tempeh can provide up to 2.5g of phenylalanine per 200 calorie per serve.