title: A comparison of 'visible' and 'invisible' users of amphetamine, cocaine and heroin: two distinct populations?
abstract: OBJECTIVE
  To compare the characteristics of heroin, cocaine and amphetamine users having no history of contact with services with those of a group in contact.
  
  
  METHODS
  Multiple agency sampling and field work which included 'snowballing' using 'privileged access interviewers'. Each subject underwent a structured interview which included the Severity of Dependency Scale (SDS), and completed a confidential, self-report questionnaire.
  
  
  METHODS
  Three contrasting provincial urban locations.
  
  
  METHODS
  Five hundred and eighty-one regular users of the target drugs. Of these, 380 (65%) denied any contact with police or helping agencies in connection with drug use.
  
  
  RESULTS
  Most zero-contact users (79%) expressed little or no concern about their drug use, and no wish for help or advice. They were much more likely to use stimulants only; less likely ever to inject any drug or, for those that did, to share equipment; less likely to use opioids, amphetamine or cocaine powder on a daily basis; more likely to use Ecstasy; and yielded significantly lower SDS scores for all target drugs save crack. Prevalence of crack use was lower, but the proportion of daily users was the same as in the contact group. Most (69%) contact users remained concerned about their drug use, but 58% expressed little or no confidence that local services could meet their needs. In both groups, SDS scores for cocaine powder were comparable to those for cannabis, LSD and Ecstasy. Of the 495 cannabis smokers identified (85% of the sample), 72% reported daily consumption.
  
  
  CONCLUSIONS
  The findings are consistent with the hypothesis that 'visible' and 'invisible' drug users are distinct populations in terms of behavioral characteristics, vulnerability to compulsive use, and prevalence of drug-related problems or concern. Purchasers and providers with limited resources should concentrate on improving the range and quality of services for users already in contact rather than attempting to uncover invisible populations. On the basis of SDS scores, cocaine HCI seems to have a relatively modest addictive potential.
authors.affiliation: Chilton Clinic, Warneford Hospital, Oxford, UK.
authors.forename: P
authors.initials: P
authors.lastname: Robson
authors.forename: M
authors.initials: M
authors.lastname: Bruce
mesh_terms: D000293:Adolescent; D000328:Adult; D019969:Amphetamine-Related Disorders / Q000453:epidemiology; D003042:Cocaine; D004739:England / Q000453:epidemiology; D005260:Female; D003932:Heroin; D006801:Humans; D008297:Male; D015995:Prevalence; D019966:Substance-Related Disorders / Q000453:epidemiology*; D014504:Urban Health
chemical_list: D003932:Heroin; D003042:Cocaine