If your child is having chronic pain, you might want to check out these articles. The first article I found this weekend and just sent it on to our doctor. The other articles I sent last week and they got our doctors attention. I got a personal phone call from him on Friday. He wanted to run the NR2 subunits NMDA receptors testing. The research is out but the testing is still in research. So the the testing cannot be done. Our doctor called in the 7mg extended release Namenda prescription to be given at a higher dosage. My son was started on the Namenda(memantine) 5 mg pills back in November and it was not until December that he noticed his headache pain levels had dropped some. According to some of the research, it can take up to 6 months for this medication to help. It helps regulate NMDA receptors but according to Wiki it also helps regulate dopamine receptors.
http://www.uic.edu/labs/wanglab/PDF/tfp2.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3113704/
http://paperity.org/p/4445327/targeting-the-nmda-receptor-subunit-nr2b-for-the-treatment-of-neuropathic-pain