I've been doing extensive reading on the difference between the two forms of phenylalanine...the D and L versions (DPA and DLPA respectively), in an attempt to understand the reaction I seem to be having to them. Almost everything I have read seems to indicate that the D version does not convert into the neurotransmitters...tyrosine, noreprinephrine, etc. Instead it inhibits enkephalin degradation. I have problems with chronic inflammatory pain, anxiety, depression, and headaches. I have achieved good results with 5-HTP on mood and anxiety, but am confused about my response to the DPA, DLPA. I seemed to have a lot of anxiety on the DLPA as well as a good level of pain relief. I switched to the D-version (DPA) thinking this should eliminate the part that could be causing anxiety (possible too much norepinephrine?), but I seem to be getting a racing heart while on the DPA. I am trying to figure how the DPA could be causing this. I want to stay on it for pain relief and it doesnt make sense to me why it would be causing racing heart. On 1000mg per day of DPA, I get excellent pain relief, but also constipation and the racing heart. I should mention that I am on a low-dose of Elavil (10-20mg per day), which works on serotonin and noradrenergic pathways, I believe. Any feedback about what might be going on would be much appreciated. Thanks.