law enforcement conflict with law enforcement removal of legal barriers to the operation of neps and other syringe access initiatives has been identified as an important part of a comprehensive approach to reducing hiv transmission among idus. legal barriers include both "law on the books" and "law on the streets", i.e., the actual practices of law enforcement officers, which may or may not reflect relevant law. changes in syringe and drug control policy can be ineffective in reducing such barriers if police continue to treat syringe possession as a crime or participation in nep as evidence of criminal activity. although most us neps operate legally, many report some form of police interference. in a 2009 national survey of 111 us nep managers, 43% reported at least monthly client harassment, 31% at least monthly unauthorized confiscation of clients' syringes, 12% at least monthly client arrest en route to or from nep and 26% uninvited police appearances at program sites at least every 6 months. in multivariate modeling, legal status of the program (operating legally vs illegally) and jurisdiction's syringe regulation environment were not associated with frequency of police interference. a detailed 2011 analysis of nep client experiences in los angeles suggested that as many as 7% of clients report negative encounters with security officers in any given month. given that syringes are not prohibited in the jurisdiction and their confiscation can only occur as part of an otherwise authorized arrest, almost 40% of those who reported syringe confiscation were not arrested. this raises concerns about extrajudicial confiscation of personal property. approximately 25% of the encounters detailed by respondents involved private security personnel, rather than local police. similar findings have emerged internationally. for example, despite instituting laws protecting syringe access and possession and adopting neps, idus and sex workers in mexico's northern border regions report frequent syringe confiscation by law enforcement personnel. in this region as well as elsewhere, reports of syringe confiscation are correlated with increases in risky behaviors, such as groin injecting, public injection and utilization of pharmacies. these practices translate to risk for hiv and other blood-borne diseases. racial gradient neps serving predominantly idus of color may be almost four times more likely to report frequent client arrest en route to or from the program and almost four times more likely to report unauthorized syringe confiscation. a 2005 study in philadelphia found that african-americans accessing the city's legally operated exchange decreased at more than twice the rate of white individuals after the initiation of a police anti-drug operation. these and other findings illustrate a possible mechanism by which racial disparities in law enforcement can translate into disparities in hiv transmission. notably, the majority (56%) of respondents reported not documenting adverse police events; those who did were 2.92 times more likely to report unauthorized syringe confiscation. these findings suggest that systematic surveillance and interventions are needed to address police interference. causes police interference with legal nep operations may be partially explained by training defects. a study of police officers in an urban police department four years after the decriminalization of syringe purchase and possession in the us state of rhode island suggested that up to a third of police officers were not aware that the law had changed. this knowledge gap parallels other areas of public health law, underscoring pervasive gaps in dissemination. even police officers with accurate knowledge of the law, however, reported intention to confiscate syringes from drug users as a way to address problematic substance use. police also reported anxiety about accidental needle sticks and acquiring communicable diseases from idus, but were not trained or equipped to deal with this occupational risk; this anxiety was intertwined with negative attitudes towards syringe access initiatives. training and interventions to address law enforcement barriers us neps have successfully trained police, especially when framed as addressing police occupational safety and human resources concerns. preliminary evidence also suggests that training can shift police knowledge and attitudes regarding neps specifically and public health-based approaches towards problematic drug use in general. according to a 2011 survey, 20% of us neps reported training police during the previous year. covered topics included the public health rationale behind neps (71%), police occupational health (67%), needle stick injury (62%), neps' legal status (57%), and harm reduction philosophy (67%). on average, training was seen as moderately effective, but only four programmes reported conducting any formal evaluation. assistance with training police was identified by 72% of respondents as the key to improving police relations. advocacy organizations ranging from the nih, cdc, the american bar association, the american medical association, the american psychological association, the world health organization and many others endorsed low-threshold programmes including needle exchange. needle exchange programmes have faced opposition on both political and moral grounds. advocacy groups including the national district attorneys association (ndaa), drug watch international, the heritage foundation, drug free australia, and so forth and religious organizations such as the catholic church. in the united states nep programmes have proliferated, despite lack of public acceptance. internationally, needle exchange is widely accepted. research disease transmission two 2010 'reviews of reviews' by a team originally led by norah palmateer that examined systematic reviews and meta-analyses on the topic found insufficient evidence that nsp prevents transmission of the hepatitis c virus, tentative evidence that it prevents transmission of hiv, and sufficient evidence that it reduces self-reported risky injecting behaviour. in a comment palmateer warned politicians not to use her team's review of reviews as a justification to close existing programmes or to hinder the introduction of new needle-exchange schemes. the weak evidence on the programmes' disease prevention effectiveness is due to inherent design limitations of the reviewed primary studies and should not be interpreted as the programmes lacking preventive effects. the second of the palmateer team's 'review of reviews' scrutinised 10 previous formal reviews of needle exchange studies, and after critical appraisal only four reviews were considered rigorous enough to meet the inclusion criteria. those were done by the teams of gibson (2001), wodak and cooney (2004), tilson (2007) and käll (2007). the palmateer team judged that their conclusion in favour of nsp effectiveness was not consistent with the results from the hiv studies they reviewed. the wodak and cooney review had, from 11 studies of what they determined as demonstrating acceptable rigour, found 6 that were positive regarding the effectiveness of nsps in preventing hiv, 3 that were negative and 2 inconclusive. however a review by käll et al. disagreed with the wodak and cooney review, reclassifying the studies on nsp effectiveness to 3 positive, 3 negative and 5 inconclusive. the us institute of medicine evaluated the conflicting evidence of both drs wodak and käll in their geneva session and concluded that although multicomponent hiv prevention programmes that include needle and syringe exchange reduced intermediate hiv risk behavior, evidence regarding the effect of needle and syringe exchange alone on hiv incidence was limited and inconclusive, given "myriad design and methodological issues noted in the majority of studies." four studies that associated needle exchange with reduced hiv prevalence failed to establish a causal link, because they were designed as population studies rather than assessing individuals. neps successfully serve as one component of hiv prevention strategies. multi-component hiv prevention programmes that include nse reduce drug-related hiv risk behaviors and enhance the impact of harm reduction services. tilson (2007) concluded that only comprehensive packages of services in multi-component prevention programmes can be effective in reducing drug-related hiv risks. in such packages, it is unclear what the relative contribution of needle exchange may be to reductions in risk behavior and hiv incidence. multiple examples can be cited showing the relative ineffectiveness of needle exchange programmes alone in stopping the spread of blood-borne disease. many needle exchange programmes do not make any serious effort to treat drug addiction. for example, david noffs of the life education center wrote, "i have visited sites around chicago where people who request info on quitting their habit are given a single sheet on how to go cold turkey -- hardly effective treatment or counseling." a 2013 systematic review found support for the use of neps to prevent and treat hiv and hcv infection. a 2014 systematic review and meta-analysis found evidence that neps were effective in reducing hiv transmission among injection drug users, but that other harm reduction programmes have probably also contributed to the decrease in hiv incidence. neps appear to be as effective in low- and middle-income countries as in high-income ones. worker training lemon and shah presented a 2013 paper at the international congress of psychiatrists that highlighted lack of training for needle exchange workers and also showed the workers performing a range of tasks beyond contractual obligations, for which they had little support or training. it also showed how needle exchange workers were a common first contact for distressed drug users. perhaps the most concerning finding was that workers were not legally allowed to provide naloxone should it be needed. drug use according to a 2022 study by vanderbilt university economist analisa packham, syringe exchange program reduce hiv rates by 18.2 percent but lead to greater drug use. syringe exchange programmes increased drug-related mortality rates by 11.7 percent and opioid-related mortality rates by 21.6 percent. arguments for and against needle disposal