AnalgesicsAnalgesics, OpioidReceptors, Opioid, muReceptors, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesAnalgesics, Non-NarcoticMorphineNarcotic AntagonistsPainAnalgesiaNaloxonePain MeasurementOpioid-Related DisordersNaltrexonePain, PostoperativeEnkephalinsTramadolNarcoticsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Drug ToleranceBuprenorphineEndorphinsEnkephalin, D-Penicillamine (2,5)-FentanylDynorphinsPhenacetinAcetaminophenPain ThresholdHydromorphoneEnkephalin, LeucineMorphinansDextropropoxypheneCodeineInjections, SpinalEnkephalin, Leucine-2-AlanineHyperalgesiabeta-EndorphinAnti-Inflammatory Agents, Non-SteroidalMeperidinePain ManagementPentazocineDose-Response Relationship, DrugMethadoneBenzeneacetamidesPain, IntractableDiprenorphineButorphanolAnesthetics, LocalHydrocodoneChronic PainOxymorphoneMorphine DerivativesDouble-Blind MethodDipyroneAnalgesia, EpiduralLevorphanolAnalgesia, Patient-ControlledBenzomorphansBupivacaineRats, Sprague-DawleyOxycodoneNociceptorsAlfentanilCyclazocineNociceptionNalbuphineSubstance Withdrawal SyndromePrescription DrugsPyrrolidinesHeroinNeuralgiaTolmetinCarrageenanKetoprofenSufentanilMeptazinolKetorolacAcupuncture AnalgesiaMorphine DependenceNalorphineKidney Papillary NecrosisNociceptive PainDrug OverdoseAcute PainPeriaqueductal GrayNefopamPrescription Drug MisuseSpinal CordCyclohexanecarboxylic AcidsIbuprofenOpiate Substitution TreatmentDrug InteractionsAnalgesia, ObstetricalBehavior, AnimalKetamineEdemaOligopeptidesDiclofenac