Harm ReductionDrug UsersSubstance Abuse, IntravenousNeedle-Exchange ProgramsNeedle SharingMethadoneHIV InfectionsStreet DrugsSyringesTobacco, SmokelessOpiate Substitution TreatmentRisk-TakingSubstance-Related DisordersDrug and Narcotic ControlLaw EnforcementHeroin DependenceCodependency (Psychology)Group StructureHepatitis CPrisonsOpioid-Related DisordersNew York CityTobacco IndustryNarcoticsPoliceSubstance Abuse Treatment CentersPrisonersBritish ColumbiaHungarySan FranciscoSelf-Help GroupsSexual BehaviorSex WorkersProstitutionHomeless PersonsPrevalenceRisk Reduction BehaviorPublic PolicyHealth PolicySocial NetworkingSmoking CessationPublic HealthMarketingBaltimoreHeroinRisk FactorsInterviews as TopicAttitude to HealthVietnamArgentinaPublic OpinionHIV SeroprevalencePeer GroupAlcohol DrinkingCondomsHIV SeropositivityCross-Sectional StudiesSmokingUnsafe SexDrug OverdoseCrack CocaineUnited StatesHIVAlcoholismHealth Services AccessibilityQuestionnairesProfessional-Patient Relations