Opioid-Related DisordersBuprenorphineAnalgesics, OpioidMethadoneNarcotic AntagonistsBehavior, AddictiveOpiate Substitution TreatmentNaloxoneReceptors, Opioid, muHeroin DependenceNarcoticsReceptors, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesSubstance-Related DisordersNaltrexoneMorphineEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-DynorphinsSubstance Withdrawal SyndromeCocaineEndorphinsEnkephalin, D-Penicillamine (2,5)-RewardSubstance Abuse Treatment CentersHeroinSelf AdministrationTobacco Use DisorderPainEnkephalin, LeucineDrug ToleranceEnkephalin, Leucine-2-AlanineDiprenorphineCompulsive BehaviorNucleus AccumbensAnalgesicsPrescription Drug MisuseAlcoholismOpiumbeta-EndorphinDopamine Uptake InhibitorsStreet DrugsMorphine DependenceBenzeneacetamidesHydromorphonePain MeasurementDopamineDrug-Seeking BehaviorNicotineConditioning, OperantMorphinansFentanylBehavior, AnimalDose-Response Relationship, DrugBrainRats, Sprague-DawleyReinforcement (Psychology)MotivationImpulsive BehaviorAnalgesiaPyrrolidinesCentral Nervous System StimulantsBenzomorphansLimbic SystemChronic PainMethamphetamineAmphetamine-Related DisordersVentral Tegmental AreaPrescription DrugsGamblingDrug Overdose