Why do so many people with ADHD have problems with cocaine, meth and sex addiction?

ADD. The drug issue is believed to be, in part, a self medication. Meth and Cocaine are of the family of medications, psychostimulants, that are used for treating add. In fact, meth- methamphetamine, is called desoxyn, as a name brand pharmaceutical used as an rx for add. The sex addiction, as well as risk taking activities in general, seem to act as stimulants, probably by adrenaline release.
Stimulation. Noradrenaline is the brain's stimulant and much more powerful than adrenaline in keeping the brain engaged and sharp. Imagine that your brain can't manage to create enough so that you routinely make errors that cost you your job, security, and relationships. So, the "fast-lane" approach, despite its dangers, gives adrenaline that may "help." the body seeks answers, science looks for better ones.