On an individual level, there is a difference in the analgesic response to a given opioid. Various factors such as gender, age, and genetic variation can affect the analgesic response. The genetic variation can influence pharmacokinetics (eg drug transporters and drug-metabolizing enzymes) and/or pharmacodynamics (eg opioid receptor and catechol-O-methyltransferase enzymes). We present recent experimentally induced pain, postoperative pain, and cancer pain and chronic non-malignant pain conditions studies in humans, focusing on the association between genetic variation and analgesic response assessed as opioid consumption or changes in pain scores. Studies have shown promising results regarding pharmacogenetics as a diagnostic tool for predicting the individual response to a given opioid in the experimental settings; however, in the clinic, it is a more complicated task to accomplish.