D-phenylalanine is the "mirror-image" of L-phenylalanine, which is the form found in proteins and foods. Your body can make L-phenylalanine but can not make D-phenylalanine.

There are couple of reports which suggest that D-phenylalanine may help with chronic pain. They have design flaws which mean that their conclusions are unreliable and no subsequent studies have been reported.

The information here may help you to decide about this http://www.umm.edu/health/medical/al.../phenylalanine.