NaloxoneNarcotic AntagonistsMorphineReceptors, OpioidEndorphinsPrimary PreventionEnkephalin, MethionineBuprenorphineReceptors, Opioid, muNarcoticsAnalgesics, OpioidOpioid PeptidesMorphine DependenceEnkephalinsbeta-EndorphinOpioid-Related DisordersEnkephalin, LeucineSecondary PreventionCenters for Disease Control and Prevention (U.S.)Drug OverdoseSubstance Withdrawal SyndromeReceptors, Opioid, kappaAnalgesicsNaltrexoneEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, Opioid, deltaAccident PreventionDose-Response Relationship, DrugDrug ToleranceMorphinansLoperamidePentazocineEnkephalin, Leucine-2-AlanineNalorphineLevallorphanLevorphanolCyclazocineEnkephalin, D-Penicillamine (2,5)-OxycodonePainDynorphinsAdministration, SublingualRisk FactorsPain MeasurementInjections, SpinalMeptazinolInjections, IntraventricularFentanylTime FactorsHeroin DependenceHIV InfectionsHeroinUnited StatesPreventive Health ServicesRats, Sprague-DawleyDiprenorphineEtorphineMeperidineHealth PromotionDouble-Blind MethodOpiate AlkaloidsPyrrolidines