ABSTRACT
Pain is one of the most basic clinical symptoms seen by every physician and is often the primary reason that patients seek medical advice. Over 100 million patients experience acute or chronic pain annually in the United States caused by headache, muscle strains and sprains, arthritis, trauma, cancer, surgery, and back injuries, among others. Because pain impairs one’s ability to carry out a productive life, pain in general and chronic pain in particular are serious health and economic problems.
