Paying people to be healthy

User Financial Incentives (UFIs) have emerged as a powerful tool for health promotion. Strong evidence suggests that large enough incentives paid to individuals conditional on behaviour they can control encourages more of the desired behaviour. However, such interventions can have unintended consequences for non-targeted behaviours. Implementation difficulties that result in individuals not understanding the nature of the incentive, unintended opportunities to "game" the system and inefficient roll-outs, can dampen results. Moreover, the legitimacy of paternalistic interventions by health planners requires careful consideration if we accept that the families involved will almost certainly be better judges of their own best interests than outsiders.