NarcoticsAnalgesicsAnalgesics, OpioidNalorphineDrug and Narcotic ControlAnalgesics, Non-NarcoticMorphineLevorphanolMeperidineNarcotic AntagonistsPentazocineAnalgesiaPainLevallorphanPain MeasurementPain, PostoperativeDextropropoxypheneMorphinansFentanylCyclazocineCodeineOpiumDopamine AgonistsAlphaprodineOxymorphoneOpioid-Related DisordersReceptors, Opioid, muLegislation, DrugMethadoneDose-Response Relationship, DrugTramadolOxycodoneDrug ToleranceHydrocodoneAcetaminophenReceptors, OpioidHeroinPhenacetinPreanesthetic MedicationPain ManagementHydromorphoneGABA AgonistsPain, IntractableAdrenergic alpha-2 Receptor AgonistsAnesthetics, LocalButorphanolPurinergic P1 Receptor AgonistsBupivacaineNaltrexoneAnti-Inflammatory Agents, Non-SteroidalBuprenorphineMorphine DerivativesNicotinic AgonistsAlfentanilMuscarinic AgonistsSubstance-Related DisordersRats, Sprague-DawleySpasmAnalgesia, Patient-ControlledPain ThresholdNaloxoneDouble-Blind MethodEndorphinsAdrenergic AgonistsSerotonin 5-HT2 Receptor AgonistsTime FactorsMorphine DependenceSerotonin 5-HT1 Receptor AgonistsHyperalgesiaInert Gas NarcosisMethotrimeprazineAdrenergic alpha-AgonistsEnkephalinsAnesthesiaNitrous OxideReceptors, Opioid, deltaHistamine AgonistsReceptors, Opioid, kappaHypnotics and SedativesPurinergic P2 Receptor AgonistsDrug InteractionsAlcoholics AnonymousGABA-A Receptor AgonistsSubstance Withdrawal SyndromeAdrenergic beta-AgonistsMitragynaDipyroneBridged CompoundsNerve BlockIsonipecotic AcidsInjections, SpinalPapaverDrug OverdoseClonidineKetonesCholinergic AgonistsParamethasoneEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Adenosine A1 Receptor AgonistsCannabinoid Receptor Agonists