Tyrosine MUST be taken with 5HTP (or tryptophan ). When you raise one neurotransmitter pre-cursor you lower the other. Tyrosine also does not produce a tolerance. You need to start taking methylation co-factors to keep it working. Cystiene being the best. You don't need to take 5htp or tyrosine apart, or on an empty stomach or with a carbohydrate. Little was understood about amino acids but now it is being discovered that there is a lot of myth surrounding their use.
Google Dr. Dan Kalish- Brain drain, which is a very good podcast.