about 10 million people in spain suffer from chronic pain. despite the identification of important steps in the mechanisms of pain, an unacceptably large number of people live with it chronically. since melzack and wall framed the idea of the central nervous system filtering, assessing and modulating the sensory information with their gate-control theory in 1965, we have advanced our understanding of the pain process. in this paper, i review the pathophysiological and molecular bases of pain, and explain the reasons why we do not have the tools to adequately treat all chronic or acute pain. of the current 100 clinical trials of pain relievers conducted by investigators from the national institutes of health in the united states, most of them are investigating new ways to deliver old standards or alternative approaches. with the help of the new science of genomics, we are discovering that there are genetic differences among individuals in response to drugs.