Opioid-Related DisordersBuprenorphineNarcotic AntagonistsOpiate Substitution TreatmentAnalgesics, OpioidMethadoneNaloxoneNarcoticsReceptors, Opioid, muReceptors, OpioidSubstance Withdrawal SyndromeNaltrexoneHeroin DependenceMethadyl AcetateBehavior, AddictiveReceptors, Opioid, deltaReceptors, Opioid, kappaMorphine DependenceOpiate AlkaloidsHeroinSubstance-Related DisordersOpioid PeptidesMorphineSheltered WorkshopsPrescription Drug MisuseCocaine-Related DisordersSubstance Abuse Treatment CentersSubstance Abuse DetectionHydromorphoneDiprenorphineNeonatal Abstinence SyndromePrescription DrugsDrug ToleranceUrine Specimen CollectionAlcoholismPainCocaineDrug InteractionsDose-Response Relationship, DrugTobacco Use DisorderTreatment OutcomeEnkephalinsCounselingDiagnostic and Statistical Manual of Mental DisordersMedication AdherenceEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Substance Abuse, IntravenousDynorphinsBehavior TherapyTime FactorsDouble-Blind MethodEndorphinsDrug Administration ScheduleDrug CombinationsEnkephalin, D-Penicillamine (2,5)-RewardUnited StatesPrimary Health CareChronic DiseaseSelf AdministrationHIV InfectionsEnkephalin, LeucineEnkephalin, Leucine-2-AlanineCombined Modality TherapyNicotineStreet DrugsCompulsive BehaviorSeverity of Illness IndexAnalgesicsNucleus AccumbensDopamine Uptake InhibitorsOpiumCase-Control Studiesbeta-EndorphinDopamineBrainMotivationBenzeneacetamidesPain MeasurementConditioning, OperantRats, Sprague-DawleyBehavior, AnimalAmphetamine-Related DisordersDrug-Seeking BehaviorMorphinansFentanylImpulsive BehaviorReinforcement (Psychology)MethamphetamineAlcohol DeterrentsCentral Nervous System StimulantsKineticsMarijuana AbuseAnalgesiaPyrrolidinesLimbic SystemBenzomorphansChronic PainGamblingSmoking