Heroin DependenceMorphineMorphine DerivativesMethadoneNarcoticsHeroinAnalgesics, OpioidMorphine DependenceBuprenorphineReceptors, Opioid, muBehavior, AddictiveNaloxoneDrug ToleranceNuclear Receptor Subfamily 4, Group A, Member 2Opioid-Related DisordersNarcotic AntagonistsSubstance-Related DisordersSubstance Withdrawal SyndromeCryptochromesCodeineReceptors, OpioidNaltrexonePainLinkage DisequilibriumPain MeasurementAnalgesiaCocaineSelf AdministrationAnalgesicsOxycodoneInjections, SpinalDose-Response Relationship, DrugGenetic Predisposition to DiseaseEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Gene FrequencyHydromorphoneRewardGenetic TestingEnkephalinsStreet DrugsFentanylPain, PostoperativeRats, Sprague-DawleyReceptors, Opioid, deltaReceptors, Opioid, kappaBehavior, AnimalNucleus AccumbensHaplotypesOpioid PeptidesOpiumSubstance Abuse Treatment CentersPolymorphism, Single NucleotideConditioning, OperantGenotypeTobacco Use DisorderSubstance Abuse DetectionEndorphinsDopamineOpiate Substitution TreatmentDopamine Uptake InhibitorsDrug OverdoseAnalgesia, Patient-ControlledDrug-Seeking BehaviorCompulsive BehaviorNalorphineMeperidineReinforcement (Psychology)OxymorphonePeriaqueductal GrayBrainPain, IntractableAlcoholismDynorphinsDrug InteractionsMorphinansNicotineDrug and Narcotic ControlPrescription Drug MisuseEnkephalin, D-Penicillamine (2,5)-NalbuphineTime FactorsMotivationTramadolVentral Tegmental AreaMethamphetamineEnkephalin, MethioninePain ThresholdCentral Nervous System StimulantsPentazocineMotor ActivityLimbic SystemAmphetamine-Related DisordersConditioning (Psychology)Analgesia, EpiduralEuphoriaImpulsive BehaviorInjections, IntravenousExtinction, PsychologicalSubstance Abuse, IntravenousPrescription Drugs