BMC Public Health 2008, 8:149 http://www.biomedcentral.com/1471-2458/8/149 though smaller, effect was observed for those aged 45 to 55 years. ing times on treatment outcomes can be made in this study. Encouraging treatment participation among younger drug users is a well-recognised problem [14]. Younger drug users are less likely to view their drug use as problematic or view themselves as dependent upon drugs [27] and young drug users living in affluent areas may be some- what protected from the negative consequences of drug use from their affluent families. It is not clear why older drug users living in the most deprived environmental con- ditions were the least likely to drop out and this finding warrants further consideration. It should be noted how- ever, that an ecological, rather than individual, measure of deprivation was used and that affluent individuals live in deprived areas and visa versa. It is conceivable that afflu- ent areas have a lower prevalence of problematic drug use and lower levels of service provision and that younger drug users with less motivation to change are deterred from using services to which they have to travel. Travelling more than one mile to treatment has been shown in one USA-based study to reduce the likelihood of a person completing treatment by a half after the effects of demo- graphic differences and the type of drugs used were con- trolled [28] and the possible impact of travelling to services requires further consideration in the UK. Controlling for the effect of deprivation and other explan- atory factors, significant differences in the odds of drop out were observed for different areas of the North West of England with the odds greater among residents of Cum- bria and Lancashire and Greater Manchester than Chesh- ire and Merseyside. Further work is needed to understand what is different about these regions and what factors dif- ferentially affect drop out. It is possible that there are dif- ferences between these areas in the manner in which treatment is delivered, or differences in client satisfaction with the treatment process and it is important to consider the potential influence of the quality of treatment on drop out rates rather than simply emphasising the role of client characteristics [10]. At the service rather than regional level, previous UK-based work has already demonstrated the effect the service can make on the number of clients retained successfully in treatment for six months [29]. The time people wait to access treatment will also influence retention. Here, a person was deemed to be in continuous treatment if they reappeared in treatment within three weeks of leaving the first agency they were in contact with. Individuals who dropped out of service and did not reap- pear until more than three weeks had elapsed were recorded as having dropped out so geographical areas whose waiting times were longer than three weeks would have a greater proportion of people reported as dropping out. Unfortunately, no assessment of the impact of wait- The only substance significantly associated with outcomes was alcohol, with alcohol users less likely to drop out of treatment than non-alcohol users. Following adjustment for other variables, opiate use was found not be signifi- cantly associated with treatment outcomes. The only large-scale longitudinal, prospective cohort study of treat- ment outcomes in the UK reported that there was no long- term reduction in drinking among patients of drug treat- ment programmes and authors concluded that poor drinking outcomes required urgent attention [30]. That alcohol use is considered as part of the overall drug profile of people contacting drug treatment is therefore encourag- ing, particularly in light of the role of alcohol in drug- related deaths [31,32] and its exacerbation of chronic hep- atitis C, currently the most significant infection affecting drug users who inject in the UK [33]. It is possible, how- ever, that this finding is a feature of reporting. The NDTMS records up to three drugs for each person, with those identified as most problematic (used most fre- quently, associated with greatest health and criminal con- sequences) reported preferentially. Alcohol is generally perceived to be less problematic than illicit drugs and individuals whose drug profile does not include alcohol may represent drug users who use a larger range of illicit drugs – those with the most severe drug problems. Alco- hol use may therefore act as a proxy measure of less severe drug problems. A recent investigation into the characteris- tics of drug users in contact with structured drug treatment reported that those whose drug profiles included alcohol as a supplementary drug were younger, were less likely to use heroin and were more likely to be referred into treat- ment via the criminal justice system [34]. Previous research in the North West of England showed that those referred from the criminal justice system were significantly more likely to drop out and less likely to complete treatment drug free than those referred from non-criminal justice sources [18]. Here the route of refer- ral was not significantly associated with treatment drop out in the bivariate analysis. Most community sentences last longer than 12 weeks; the now defunct Drug Treat- ment and Testing Orders for example (orders that required the offender to attend regularly both court and treatment and provide a urine sample for drug testing) became available nationally in October 2000 and could last between six months and three years [35]. It is there- fore conceivable that those referred from the criminal jus- tice system were retained in treatment for 12 weeks due to fear of breaking their order but had poorer long-term out- comes because they lacked the intrinsic motivation for behaviour change. However, the identification of poorer outcomes for criminal justice referrals [18] relates to out- Page 9 of 11 (page number not for citation purposes)