AnalgesicsAnalgesics, OpioidAnalgesics, Non-NarcoticPainMorphineAnalgesiaPain MeasurementNarcoticsNaloxoneOxycodoneOpioid-Related DisordersTramadolFentanylNarcotic AntagonistsReceptors, OpioidPain, PostoperativeOpioid PeptidesEnkephalin, MethionineDrug ToleranceEnkephalin, Ala(2)-MePhe(4)-Gly(5)-CodeineHydromorphoneEndorphinsReceptors, Opioid, kappaPhenacetinAcetaminophenPain, IntractableEnkephalinsDextropropoxypheneMeperidineInjections, SpinalChronic PainBuprenorphineOxymorphonePain ThresholdReceptors, Opioid, deltaAlfentanilNaltrexonePain ManagementHydrocodonePrescription DrugsHyperalgesiaEnkephalin, D-Penicillamine (2,5)-Analgesia, EpiduralSufentanilAnesthetics, LocalAnti-Inflammatory Agents, Non-SteroidalDose-Response Relationship, DrugMorphine DerivativesAnalgesia, Patient-ControlledPentazocinebeta-EndorphinBupivacaineDouble-Blind MethodDipyroneNeuralgiaNociceptive PainMethadoneDynorphinsHypnotics and SedativesEnkephalin, LeucineReceptors, Opioid, muPrescription Drug MisuseAcute PainNociceptorsBenzeneacetamidesKetorolacTolmetinMorphinansNalbuphineButorphanolRats, Sprague-DawleyLevorphanolNociceptionAnalgesia, ObstetricalCyclohexanecarboxylic AcidsHeroinEtorphinePeriaqueductal GrayOpiate AlkaloidsDrug PrescriptionsCarrageenanKetoprofenKidney Papillary NecrosisNefopamCyclazocineSpinal CordKetamineDrug and Narcotic ControlDrug InteractionsIbuprofenEnkephalin, Leucine-2-AlanineClonidineDrug OverdoseChronic DiseasePyrrolidinesNalorphinePiperidinesAcupuncture AnalgesiaNerve Block