- Currently Scotland operates an opt in system of organ and tissue donation. This review was undertaken to provide an overview of evidence regarding opt out systems of donation and to inform the development and implementation of a workable opt out system of organ and tissue donation
- The majority of the Scottish population is likely to support opt out legislation for organ donation (59% supported the principle of opt out in a 2016 TNS survey  )
Although, there is little firm evidence that opt out legislation in isolation causes increases in organ donation and transplantation, there is encouraging evidence that, as part of a package of measures, opt out legislation can lead to increases in organ donation and transplantation.
- A body of evidence shows that there is a well-established association between higher deceased donation/transplantation and opt out legislation/systems compared to opt in. Although it is important to note that not all opt out countries have higher rates of deceased donation and transplantation
- A range of before and after studies suggest a change to a system of opt out donation can result in increases in organ donation, although this evidence base is somewhat limited
- A small body of evidence from psychological experiments explains how opt out could increase donation and transplant, although its real word applicability is limited
- It is challenging to separate the impact of opt out legislation from other concurrent system changes, thereby limiting the evidence base
- There is some encouraging but limited evidence that opt out systems can bring about wider positive changes, which are likely to increase organ donation and transplantation
- There is a small body of international evidence that suggests opt out is associated with increased willingness to donate. People in opt out countries were between 17–29 per cent more likely to report willingness to donate their own organs and 27–56 per cent more likely to authorise the donation of their own relatives' organs, compared to respondents living in opt in countries
- There is a limited body of evidence with regards to the impact of opt out legislation and systems on the number of people registering decisions on a register (where they are used).
- Existing evidence draws no firm conclusions about the impact of opt in legislation on family authorisation. A small number of studies suggest how family authorisation could increase as a result of opt out. However, there is also evidence ( e.g. from Chile) indicating decreases in family authorisation
- Welsh evidence suggests that opt out is likely to increase awareness of organ donation more widely, although only limited conclusions can be drawn from this
- There is a strong body of evidence that highlights the importance of non legislative measures, such as improving infrastructure. This suggests that opt out systems and legislation function most effectively as part of a wider package of measures,
- Public awareness of opt out appears to be important and associated with increased willingness to donate, particularly in opt out systems
- Public attitudes are likely to be crucial. There are several country based case studies ( e.g. Brazil) which indicate that negative public attitudes, particularly due to medical mistrust, can pose a risk when implementing opt out. There is strong evidence that families should be encouraged to have conversations about organ donation and where this happens it is likely to increase organ donation and transplantation. It is vital that families are aware of what organ donation is, when it can occur and their involvement in the process
- There is evidence which indicates that improving health care staff awareness, knowledge and confidence in relation to donation is likely to be important in raising organ donor numbers
- There are various contextual factors ( e.g. mortality rates) that are likely to influence the impact of opt out and these should be considered when comparing countries
- Religion and ethnicity are likely to be important and the relationship with organ donation is complex, but there was little evidence identified with regards to opt out on specific religious or ethnic groups.