1. Institute of Medicine. Reliving pain in America. Washington DC; 2011. p. 1. http://books.nap.edu/openbook.php?record_id=13172&page=1 . Accessed March 2, 2013.
2. National Center for Health Statistics New report finds pain affects millions of Americans. Press release issued by CDC; 2014. http://www.cdc.gov/nchs/pressroom/06facts/hus06.htm . Accessed July 11, 2014.
3. National Institutes of Health. The NIH guide: new directions in pain research 1. Washington, DC; 1996. http://grants.nih.gov/grants/guide/pa-files/PA-98-102.html . Accessed June 2013.
4. Gorji A, Khaleghi Ghadiri M. History of headache in medieval Persian medicine. Lancet Neurol. 2002;1:510–5.
5. Turnbull A. Tincture of capsaicin as a remedy for chilblains and toothache. Dublin Free Press, vol. 1; 1850. pp. 95–96.