Evolving knowledge of opioid genetics in cancer pain

Inter-individual variation in response to opioids for cancer pain is a well-established phenomenon. Variation occurs in the dose of opioid required, the analgesic efficacy of the opioid and also in the side-effects experienced by the individual taking the drug. To date, no clinical factor has been identified that can reliably explain or predict such variation. In recent years there has been growing interest in the possibility that genetic factors may play a role in the variability in opioid response. The aims of this review are to present the evidence supporting pharmacogenetic research in this area, to evaluate some of the studies and results that have been published to date and to present some of the challenges for future research in this area.