Chronic pain management represents a serious healthcare problem worldwide. Chronic pain
affects approximately 20% of the adult European population and is more frequent in women and older
people. Unfortunately, its management in the community remains generally unsatisfactory and rarely
under the control of currently available analgesics. Opioids have been used as analgesics for a long
history and are among the most used drugs; however, while there is no debate over their short term use
for pain management, limited evidence supports their efficacy of long-term treatment for chronic noncancer
pain. Therapy with opioids is hampered by inter-individual variability and serious side effects and
some opioids often result ineffective in the treatment of chronic pain and their use is controversial.
Accordingly, for a better control of chronic pain a deeper knowledge of the molecular mechanisms
underlying resistance to opiates is mandatory.