It is not very difficult to remember the difference between adopted and adoptive. Just take a look at these examples:
Mary has adopted a little boy. Now he calls her ‘mommy’.
Jeremy was adopted by Mary a year ago. He looks happy now.
Jeremy loves his adoptive mother.
Jake didn’t know his natural parents. But his adoptive parents gave him everything: love, care and support.
According to these examples we can see that ‘adopted’ is a person who was taken by somebody while ‘adoptive’ is a person who takes somebody.