MorphineAlkaloidsErgot AlkaloidsMorphine DependenceMorphine DerivativesIndole AlkaloidsPyrrolizidine AlkaloidsVinca AlkaloidsAnalgesics, OpioidCinchona AlkaloidsBerberine AlkaloidsDrug ToleranceNarcoticsAmaryllidaceae AlkaloidsNaloxoneAconitumReceptors, Opioid, muAporphinesClavicepsNarcotic AntagonistsBenzylisoquinolinesDelphiniumCatharanthusAnalgesiaPain MeasurementInjections, SpinalCodeineSolanaceous AlkaloidsPapaverSubstance Withdrawal SyndromeBerberinePain, PostoperativePlant ExtractsOpiumAnalgesicsNeotyphodiumCoptisRutaceaePlant PoisoningPainDose-Response Relationship, DrugReceptors, OpioidMolecular StructureErgotismLycopodiumErgotamineNaltrexoneMorphinansLysergic AcidRubiaceaeAnalgesia, Patient-ControlledNalorphineThebaineStereoisomerismRats, Sprague-DawleyEphedraBelladonna AlkaloidsHeroinHydromorphoneHarmineFentanylEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Periaqueductal GrayEnkephalinsAspidospermaPapaveraceaeReceptors, Opioid, deltaOxycodonePentazocineEphedrinePlants, MedicinalPlant BarkNalbuphineIsoquinolinesErgolinesAnnonaceaeSenecioHeterocyclic Compounds with 4 or More RingsUncariaBenzophenanthridinesRauwolfiaAconitineVeratrum AlkaloidsPoriferaMeperidineHypocrealesEtorphineIbogaineEpichloeLiliaceaePain ThresholdMitragynaHarmalineBehavior, AnimalOxymorphoneCorydalisCyclizationAnalgesia, EpiduralEphedra sinicaDiterpenes