Ineffective analgesic management of patients with sickle cell disease remains a major problem in the management of the disorder in both adults and children. The pharmacological treatment of acute and chronic pain conditions resulting from vaso-occlusive crises in children with sickle cell disease typically involves the use of opioids. In the outpatient setting, this is most commonly achieved with administration of codeine and/or tramadol, both substrates of cytochrome P450 2D6 (CYP2D6). Currently these drugs are used in this patient population without any information concerning the patient's capacity to metabolize these CYP2D6 substrates which may lead to over and under treatment of pain depending on their CYP2D6 activity. The proposed objectives in this application will address this issue by the development of a pharmacodynamic assessment tool that will objectively assess the response to morphine in terms of analgesic response (pharmacodynamic assessment). This new tool might also serve as a non-invasive technique for CYP2D6 phenotyping if CYP2D6 substrates are used for pain therapy by assessing specifically morphine response. Development of this novel assessment tool will result in improved opioid analgesic therapy in this population. Future anticipated studies will examine the application of this technique in the determination of opioid tolerance and hyperalgesia.