There is no evidence that methadone has increased initiation into opiate addiction where it has been made available. However, it is difficult to develop a powerful design for testing the hypothesis, particularly given the paucity of local indicators of heroin use. There has been no association between the number of persons in methadone programs and the number of reported new users in the National Household Survey on Drug Abuse, but that is at best a weak test. Assessing whether methadone prolongs a career of opiate dependence is difficult because of the very different characteristics of the methadone and heroin initiate populations. Even among addicts, many desist for long periods without treatment; for example, Anglin et al. (1986) found that 56.4% of a sample of 406 heroin addicts were able to desist for three years or more without formal assistance. However, those who initiate methadone use for addiction treatment are those who were unable to quit heroin; hence the difficulty of comparison.
Harm reduction has been controversial wherever it has been applied explicitly; moreover it often has a weak base in terms of assessed outcomes. Automobile safety is one instance for which there is good evidence of both compensatory behavior and net harm reduction. It is also the instance in which harm reduction issues have been least clearly articulated in public debate, though widely discussed in the traffic safety community.
Interventions to reduce the danger of adolescent sexual behavior have shown no adverse effect, in terms of increased sexual activity, but also little indication that the interventions have reduced the average harmfulness of the acts. For alcohol, harm reduction is gathering momentum but with only a modest scientific basis at either the population or clinical level. For heroin, research on methadone and needle exchange programs provide evidence that they do reduce total harms resulting from use by currently dependent users; there is a weaker evidentiary base for concluding that initiation is unaffected.
These examples are offered for the insights they may provide as to the likely consequences of tobacco-related potential reduced-exposure products (PREPs). However, harm reduction can work through a number of mechanisms and has consequences in a number of dimensions. Assessing the relevance of these harm reduction interventions to PREPs requires consideration of those mechanisms and consequences.