Seven years of going to ChADD national meetings and several workshops with Russ Barkley suggest the following:
a: About 5% of males will have clinically significant ADHD which is considered a continuous variable.
b: Of the ADHD kids, 62% will develop Oppositional Defiant Disorder around age 5.
c: Of the ADHD kids, 42% will develop Conduct Disorder around age 7, chiefly characterized by lying and stealing
d. ODD and CD seem to relate to parental inconsistency, family distress, depressed mothers, and antisocial behavior in one of the natural parents, usually the father.
e. ODD and CD may be precursors of APD; ADHD possibly is not.
f. ODD and CD seem to be more strongly related with drug abuse rather than drug experimentation.
I personally would wager that much of ODD will be eventually tied to mania and bipolar disorder. Many of the argumentive traits attributed to ADHD could be as easily linked to mania. This diagnositic change would also account for a lot of other "orphan" data about ADHD. The negative is that of teaching worried parents that their child may have the complication of a 2nd problem that can be more socially disruptive than ADHD.
Some recent information from Joe Biederman's group shows CD and bipolar disorder to have the same elevated risks for drug abuse in the teens and again in the late 40s.
Check your indices for articles by Russell Barkley, Rachel Gittelman Klein, and Gabriella Weiss or Lilly Hechtman for longterm outcome studies of ADHD clients. You won't find much of their work on the Net; a good library, particularly in a medical school, will give you lots of material.