There are now several strong opioids available to choose from for the relief of moderate to severe pain. On a population level, there is no difference in terms of analgesic efficacy or adverse reactions between these drugs; however, on an individual level there is marked variation in response to a given opioid. The genetic influences to this variation are complex, and although current research has shown some promising results, these have not been replicated across larger studies and as such the ultimate aim of personalized prescribing remains elusive. If personalized prescribing could be achieved this would have a major impact at an individual level to facilitate safe, effective and rapid symptom control. This review presents some of the recent positive advances in opioid pharmacogenetic studies, focusing on associations between candidate genes and the three main elements of opioid response: analgesic, upper gastrointestinal and central adverse reactions.