Direct harms

In some cases, desired health outcomes may have directly harmful effects, regardless of the content of the intervention targeting them. For example, sun exposure is associated with a reduced risk of some cancers.4 This implies that skin cancer prevention programmes which successfully reduce sun exposure may risk inadvertently increasing the risk of other cancers. Similarly, programmes to increase sports participation may increase injury risk. More generally, in many cases the evidence for the longer-term health impacts of behaviour change is lacking, as witnessed by the recent controversy over body weight and mortality sparked by the work of Flegal et al.5

Psychological harms

A more indirect category of harms is the possibility of negative psychological impacts on individuals as a result of interventions. Perhaps, most obviously, some population screening programmes may produce high numbers of false-positive results, potentially leading to substantial adverse effects in terms of psychological stress and unnecessary treatment;6–10 the NHS Health Check programme has recently been criticised on these grounds.11 Some universal psychological interventions, such as ‘debriefing’ after traumatic events, may have adverse mental health impacts.12 The dissemination of health messages through educational or media campaigns may generate damaging feelings of worry or guilt, which can have negative effects not only on general well-being but, in many cases, on the targeted behaviours themselves.13 ,14 While most media campaigns do now try to avoid explicitly guilt-oriented messages, there is still considerable potential for harms, which have rarely been investigated systematically.

More indirect psychological harms may result where targeted health behaviours are bound up with individuals’ social identity or relationships with others. It is hard to say how serious this potential for adverse effects may be, since such socio-psychological harms are rarely considered in evaluations of interventions. However, the qualitative literature suggests that, for example, moderate consumption of alcohol or other drugs may facilitate social interactions,15 ,16 and that unprotected sex may facilitate trust and intimacy within sexual relationships.17 ,18 It is thus possible that interventions targeting these behaviours could have negative impacts on social or intimate relationships.

Equity harms

Interventions may create harm by worsening health inequalities. That is, some successful interventions may improve outcomes across the population, but exacerbate existing inequalities by benefiting privileged groups more than disadvantaged groups.19–21 This has particularly been a concern with individualistic or ‘responsibilising’ approaches to health promotion which, it is often argued, tend to benefit those who are in least need of them.22 ,23 It has also been argued that targeted or ‘high-risk’ approaches are more likely than population-level initiatives to widen health inequalities.24 Although the evidence base on such ‘intervention-generated inequalities’ is limited in extent, there is fairly reliable evidence that some interventions do widen inequalities, particularly media campaigns for smoking cessation.25

Equity harms raise complex ethical and methodological questions, since they may exist even where no individual in the population is worse off as a direct result of the intervention. However, given the evidence that inequality at a societal level is itself harmful across the population as a whole,26 it is clear that effects on equity are an important dimension of the potential harms of interventions.

Group and social harms

Group-based interventions may inadvertently create harms by singling out a particular subset of the population, or by the effects of bringing them together. A particular concern in the literature has been the so-called ‘deviancy training’ effect in group-based targeted interventions with young people for outcomes such as antisocial behaviour or drug use. That is, group interventions may generate harms by facilitating social interaction between people who are already partially socialised into marginal or ‘deviant’ norms,27 ,28 although the empirical evidence is mixed.29

Targeting particular groups or behaviours for intervention may contribute to stigmatising them. This may operate at an individual level, for example, in interventions targeting obesity,30–32 or on a larger scale, where the targeting of social interventions at disadvantaged groups or areas may exacerbate the stigma experienced by their members or residents. It may also contribute to divisions between groups, as in the case of alcohol restrictions in Aboriginal communities in Australia.33 ,34

More broadly, interventions may have negative impacts at the level of social norms or perceptions. For example, advocacy to promote bicycle helmets may contribute to an exaggerated perception of the injury risks of cycling, and hence lower cycling rates.35 This type of harm overlaps with those already discussed to the extent that interventions may contribute to culturally entrenched stereotypes of, for example, drug users or people from socio-economically deprived areas, hence contributing to the broader disadvantage which these groups may suffer. Social narratives—such as those which determine the boundaries of ‘appropriate’ behaviour by pregnant women (eg, around light consumption of alcohol)—may cause stress and guilt even where their putative health rationales receive limited support from the evidence.36 Such narratives may also lead people to reject public health messages as irrelevant to them, for example, by perpetuating stereotypes of particular health risks as associated with lower or marginal status. Finally, the broader impacts of ‘medicalisation’, for example, of mental health problems, on social norms, should also be borne in mind as a potential adverse effect of preventive programmes.37

Opportunity cost harms

A final category of potential harms relates to the opportunity costs of interventions, that is, the potential benefits which may be forgone as a result of committing resources to ineffective or less effective interventions, or to less serious public health problems. Such opportunity harms cannot be precisely defined, since the counterfactuals on which they rest are imponderable by their nature, and are not limited to specific prioritisation scenarios. Nonetheless, from some perspectives such opportunity harms considerably outweigh the other categories of harms discussed above, and they should be considered in any discussion of adverse effects. Indeed, many of the other harms mentioned above—particularly in the context of large, costly intervention programmes (eg, health checks and media campaigns)—may also represent substantial opportunity cost harms.