Has he ever been tested for tics or for anxiety related issues? This can be a sign of stress or anxiety Given his adhd diagnosis and the medications, I am wondering strongly if it is a type of tic. Not a lot of people know this but MANY who are diagnosis'd with adhd, esp inattentive type (which he isn't from the sounds of it, but this is still valid), actually have undiagnosed seizure disorders.
Back when adhd was first treated, the late 70s/early 80s or so, before a child was given a stimulant they had to have an eeg to rule out seizures. Esp if the child had a history of febrile seizures. I remember this because the first add kid was the little bro of a friend and I remember talking about the eeg and all the wires coming "out" of his head (stuck on, but I was 11 and it looked cool in the polaroid they had - yes, I have a LOT of childhood memories like this.) during the test.
Now? Most docs look at you like you have a third eye if you push for this. I know not all docs will go ahead and order the test. I tossed such a big stinky hissy over this with Wiz that they did it for Jess without much complaint. Boy was I glad we insisted on the sleep deprived eeg. Wiz was totally normal so the adhd medications were fine. Jess was a different story. You KNOW something is wrong when they call you for an appointment rather than sending a letter. Jess did NOT have the inattentive adhd that her teachers, her doctor, the psychiatrist and my mother all SWORE was her problem. Jess has seizures. They are absence seizures which is a nice way of saying the house is lit up and the power is on but no one is home in there. It looks like she is staring at something. In the beginning she was having so many seizures that the neuro estimated she was missing about half of everything that was going on in her life. Her brain was just not there for HALF of her life - in 10 to 50 second chunks of tme. Finding the right seizure medication hasn't been easy but has made a HUGE HUGE difference~
Tics are neurological. They can be harmless or not. They can be a symptom of another disorder and it could be any of a wide range of things. There is also an anxiety disorder that has people pulling/twisting/yanking their hair out all the time. It is not easy to haveand I think is a type of Obsessive Compulsive Disorder (OCD). I could be very wrong on that.
Why not start keeping a log of this - did he do it before school, when he got home, at an activity? Keep this for a couple of weeks and also do some reading on har twisting/pulling, compulsive hair twisting, tics, etc.... Also just keep an eye out for any other things that might seem like tics - I am sure others can help you identify other common tics.
Once you have at least a week of notes, doesn't have to be detailed - this time/activity yes he did or no he didn't or he did and stopped, whatever is easy to keep, then ask the doctor about it. Are their other symptoms causing problems? Has this been gong on for days? weeks? months? years? all his life? That is important for the doctor to know because it might help show a pattern. Then you could work to find a way to help manage this and any other issues.