how to tell an older child hes adopted

Regarding explaining the drug use, etc., to your son, there is a book called "Telling the Truth to Your Adopted or Foster Child: Making Sense of the Past" that is very good and describes how to explain information in age appropriate ways. I forget exactly but it was something like, if the bmom had been raped, when the child is young mention that their bparents didn't know each other, and then when the child is a little older say they didn't like each other, and the tell the whole truth when the child is 10 yrs (I forget the exact age, but I remember the book emphasized that children need to know all the information, good and bad, before they hit puberty. I think it had something to do with the development of abstract reasoning and some sort of 'identity' formation in the early teen years, but I forget the details, maybe more problems if the kid finds out later and has to reform their identity at an abnormal stage of life?).