MorphinePainMorphine DependenceMorphine DerivativesAnalgesics, OpioidPain, PostoperativePain MeasurementPain ManagementChronic PainPain ThresholdDrug ToleranceNarcoticsNaloxonePain, IntractableLow Back PainBack PainAbdominal PainNeck PainAnalgesiaAnalgesicsReceptors, Opioid, muPain PerceptionNarcotic AntagonistsPelvic PainFacial PainInjections, SpinalAcute PainPain, ReferredCodeineSubstance Withdrawal SyndromeShoulder PainMusculoskeletal PainAnalgesia, Patient-ControlledReceptors, OpioidHyperalgesiaNaltrexoneDose-Response Relationship, DrugFentanylRats, Sprague-DawleyOxycodoneHydromorphoneNeuralgiaNalorphineNociceptive PainPeriaqueductal GrayHeroinEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NociceptorsPentazocineMorphinansEnkephalinsDouble-Blind MethodAnalgesia, EpiduralNalbuphineMeperidineReceptors, Opioid, deltaSpinal CordBehavior, AnimalAnesthetics, LocalAnalgesics, Non-NarcoticChronic DiseaseOxymorphoneTramadolThebaineTime FactorsBupivacaineMyofascial Pain SyndromesOpiumComplex Regional Pain SyndromesVisceral PainMethadoneLabor PainEndorphinsInjections, SubcutaneousTreatment OutcomeArthralgiaReceptors, Opioid, kappaOpioid-Related DisordersNociceptionDrug InteractionsKetorolacHot TemperatureBuprenorphinePruritusInjections, IntraventricularInjections, IntravenousProspective StudiesLocus CoeruleusMotor ActivityPapaverLevallorphanClonidineCyclohexanecarboxylic AcidsPostoperative Nausea and VomitingAnesthesia, SpinalOpioid PeptidesHydrocodoneLidocaineNerve BlockDrug Administration Schedule