ADHD is a common symptom of any of several organic dysfunctions in the brain. Because of this, any viable answer will border on medical advice, which is out of scope for SE. Nevertheless, I will attempt to give an answer (sanitized of medical advice) because I believe this is a good question.
My exposure to ADHD goes back to the late 1980's when I assisted in creating materials for a children's hospital to teach parents whose children had been diagnosed with ADD (as it was called then) about the symptoms and treatments available. Over the years, both knowledge and misinformation about the condition have abounded.
In the past year, the study of ADHD has become much more personal for me. As a result of injuries, I exhibit many of the same symptoms as children with ADHD (and @anongoodnurse keeps me in check on here when I get out of hand, much to her frustration and my deep appreciation). Unlike the children, I have a solid anatomical model that I can point to to explain what is out of whack.
Asking "How do I discipline a child with ADHD" is IMHO akin to asking "How do I discipline a child with one leg?".
A child with one leg cannot be expected to compete in the 100 meter sprints, but they can be disciplined to persevere and accomplish great athletic feats (https://www.youtube.com/watch?v=SaXU8_soOBQ)
Example:
In many of my postings talk (or brag) about my webcast team, which is first-in-class for the work they do. On my team, I have a boy with ADHD. The other day we sat down and I explained to him the nature of my injuries. It took him about 2 minutes to reason his way from the abstract discussion of brain anatomy to realizing that we shared the most troubling of his symptoms - the violent flash temper that OP describes.
Outside of my team, this boy has a reputation for an unpredictable temper. But when webcasting, this boy always incredibly focused and professional no matter how much pressure I put him under, while working in close quarters in a team, which includes at least two other people with flash tempers.
Takeaway #1: It has been documented that kids with ADHD often do better with task oriented activities than unstructured activities.
Takeaway #2 You can instill discipline (self control), but you cannot heal a mechanical flaw through punishment.
Takeaway #3 He may need to learn to handle emotions strategically rather than tactically. In my own case, due to mechanical damage, I am not aware of emotions until they are strong enough that I can read the involuntary signs in my own body. All of the drugs and anger management classes in the world can't compensate for a damaged shred of tissue that is just a few millimeters in size.
One of my tech's flash points is when he feels he is being appeased or catered to. He is not defined by ADHD. I hold him to the same standard as the adults on my team, and his ADHD only comes to my attention when outside forces intrude.
Takeaway #4 Treat him with respect, and cultivate an atmosphere of mutual respect. Nothing hurts a person's feelings more than to be treated as damaged goods by people they respect.
Takeaway #5 Do not cater to ADHD. He will have to live in the real world and learn to manage. Temper tantrums have real world ramifications. In the world of social media, a person's career can be ended and they can be rendered unemployable for one bad day.
