A huge amount of research has been done on the impact of adoption on the child's health and well-being. Some research suggests that adopted children are more likely to exhibit worse health or behaviour than non-adopted children. Some of these behaviours are linked to issues of lack of identity through the child not knowing 'where they have come from' as a result of a closed adoption. Most of this research is based on closed adoption. One of the advantages of Open Adoption is that it reduces the likelihood of identity related behavioural issues. It should be noted that there is also a large body of literature that shows no health and behavioural difference between adopted and non-adopted people.
Relatively little research has been carried out in New Zealand, where Open Adoption is now the norm.The most relevant piece of New Zealand research (Fergusson & Horwood 1998) has shown that compared to all other children, adopted children were advantaged throughout childhood in terms of childhood experiences, standards of health care, family material conditions, family stability and mother/child interaction. Compared to children born to single mothers (the source of all the adopted children) adopted children were significantly less likely to have problems in adolescence (although not as low as non adopted children born to two parent families). It should also be noted that the majority of subjects in this research would have been adopted under the old closed system.
Fergusson D, Horwood L (1998) Adoption and adjustment in adolescence. Adoption and Fostering 22:24-30