The involvement of users and stakeholders in the co-creation of services for citizens presents some critical issues when applied to prevention. In healthcare, the perimeter of effective and appropriate interventions is defined by guidelines and users often lack the tools to discuss its boundaries. It is necessary that the selection of possible interventions does not appear arbitrary, agreeing from the outset on which criteria and sources will be adopted. Furthermore, in prevention, what is identified as a need by the health service is not always perceived as such by potential users. The different assessment of needs leads to perceiving possible interventions as undue interferences in lifestyle choices.