Analgesics, OpioidReceptors, Opioid, muReceptors, OpioidOpioid-Related DisordersMorphineNarcotic AntagonistsReceptors, Opioid, deltaNaloxoneNarcoticsBuprenorphineReceptors, Opioid, kappaDrug ToleranceOpioid PeptidesPainNaltrexoneEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-EndorphinsDynorphinsEnkephalin, LeucineEnkephalin, Leucine-2-AlanineStructure-Activity RelationshipDiprenorphineMolecular StructureAnalgesicsbeta-EndorphinBenzeneacetamidesMorphinansFentanylPain MeasurementMethadoneDose-Response Relationship, DrugHydromorphoneStereoisomerismPyrrolidinesBenzomorphansMagnetic Resonance SpectroscopySubstance Withdrawal SyndromeAnalgesiaOpiate Substitution TreatmentHeroinKineticsChronic PainOligopeptidesPrescription Drug MisuseRats, Sprague-DawleyLevorphanolMorphine DerivativesMolecular Sequence DataBenzylidene CompoundsMorphine DependenceDiterpenes, ClerodaneIndicators and ReagentsButorphanolHematoporphyrin DerivativePrescription DrugsOxymorphoneLigandsChromatography, High Pressure LiquidHeroin DependenceMolecular ConformationEthylketocyclazocineRadioligand AssayAmino Acid SequenceInjections, SpinalPain, IntractableBinding, CompetitiveInhibitory Concentration 50Binding SitesAnalgesics, Non-NarcoticDrug OverdoseCell LineCyclazocineSpiro CompoundsPain ThresholdSpectrophotometry, UltravioletGuinea PigsDrug DesignChemistryDrug InteractionsTime FactorsHydrocodoneChemical PhenomenaPeriaqueductal GrayPiperidinesD-Ala(2),MePhe(4),Met(0)-ol-enkephalinHyperalgesiaModels, MolecularEscherichia coliChromatography, Thin LayerRats, WistarCricetinaeGuanosine 5'-O-(3-Thiotriphosphate)HematoporphyrinsAlfentanilNalbuphineSpectrophotometry, InfraredProtein BindingTramadol