Heroin DependenceNarcoticsMorphine DerivativesMethadoneSelf AdministrationBuprenorphineDrug OverdoseCodeineStreet DrugsCocaine-Related DisordersSubstance Abuse, IntravenousBehavior, AddictiveOpioid-Related DisordersSubstance Abuse DetectionSubstance Withdrawal SyndromeDrug and Narcotic ControlNaloxoneOpiate Substitution TreatmentMorphineNaltrexoneCocaineSubstance-Related DisordersReceptors, Opioid, muDrug UsersAnalgesics, OpioidConditioning, OperantCrimeNucleus AccumbensReinforcement (Psychology)Substance Abuse Treatment CentersLaw EnforcementGas Chromatography-Mass SpectrometryReinforcement ScheduleDose-Response Relationship, DrugExtinction, PsychologicalDrug ContaminationBehavior, AnimalPolitical SystemsCrack CocaineRats, Long-EvansSocial Determinants of HealthNeedle SharingFlupenthixolCuesInjections, IntravenousPupilSecobarbitalDrug-Seeking BehaviorSweatReceptors, Opioid, delta