I do not have ADD or ADHD but did know a close friend that did. He had the condition from birth, he told me, and was worsened from prescription medications at an early age that lasted into his teens. He tried meditating on his own a few times for relief and on one such occasion, he managed to accidentally astral project. He fell into a coma that lasted two days and when he came to, he retold of floating around his body, meanwhile, some malicious force was shadowing him keeping him from re-engaging. This mess went down before I met the fella so I can't validate any of it and remain indifferent. He avoided practise after the fact.
I found him to only have a rudimentary grasp of meditation that was sullied by lotts of woo woo nonsense, mysticism. His lense of enlightenment was the Native American's awakening or the buddhist's 4th jhana. I instructed and guided him through a few sits and learned that instead of being grounded in his physical body, his center of awareness was his prana, or energies. I established his meditative "symptoms" over some dialectic discussions and going back and forth matching circumstances with my own practice. It just seemed to me that he was navigating life under blurred sensate awareness. Clarity was obscured by inculcated ideologies and psychedelic legends.
But the clearest factor was that his meditative ability was naturally great! He was easily propelled into deep states without even trying. This could be considered dangerous as one could easily "slip" out of the body and without the necessary comprehension over what actually is happening, is what he may or may not have experienced.
Everyone is born different, some are fine genetic specimens... some, like me, are born with extra fluid in their eyes and require glasses

others are born with exceptional skills... and some are just born more sensitive to life. It's all fine of course, in the end, this is not about becoming super-human, it's about realizing that being human is super. I gave him some advice, to form some sort of fitness regimen and get to know the mechanisms of his body more. And to remember that the breath is always there as an anchor. We all have to deal with our past Karma. Meditation did finally bring relief but only after he had made newfound insights into his own nature. He still has a long path to walk but unfortunately, he says he doesn't have the time to meditate on his own

...
I'm not shy to the subject of chemical imbalances and actually I'm quite glad to have faced such phenomena too, just for the experimental aspects of the scientific investigation. My condition is somewhat rare and is also characterized by heightened dopamine levels. The first step is not to jump onto the cushion and meditate, it's acceptance. In Buddhism, one definition of a demon is a thought principle that has branched away from the "normal conscious" or a traumatic memory that split from "the mind". Denial only strengthens the demon, makes the event harder to deal with. I tried therapy for many years to no avail and refused medication. I quit therapy and took my care into my own hands, and by extension, the universe you could say

I'm able to hold down a fine job, have romantic relationships, I have a plethora of hobbies that I enjoy, and maintain good company. It's part of the treatment to keep a positive mindset! Happiness is an emotion and those cant be faked while a positive mentality is just a world view, and those get stronger the more you refine them. Sulking into depressive episodes and becoming a hermit would probably only do more harm than good. The opposite if depression isn't happiness, it is vitality!
I'm a big advocate about getting one's psychological trip in order FIRST before meditation is turned to.
Through meditation, I have learned that I am impotent against my bodily chemistry... I have noticed that only a dash of sadness causes me to break out in acne and predisposes me to sickness. I cannot sleep unless I feel adequate either, my vibrancy is too affected. Manic episodes when I was younger would leave me sleepless for days. after 4 or 5 days I would begin to pass out randomly. I remember one occurrence that happened while walking home from school... I was walking down a sidewalk and just like that
LIGHTS OUT!
I woke up 2 hours later, nothing seemed stolen; this was normal to me. And with those two hours, I would stay up for another number of days until my next moment of collapse. Meditation helped me to steady myself and instead of sleep, I would meditate to compensate for the lack of oxygen reaching my brain. Meditation, staying in good spirits, and having a grasp of the human condition acted as my cures.
I'm sure it's possible to achieve a level of manipulation over these chemicals but I haven't been able to. It's all just been about finding balance. I can say now though that I do feel "cured". Of course, it's still there, but it has no hold over me. I can use meditation to shift into sleep and it makes no impediment to my life. My mother doesn't share in my condition but she too surrenders to her bodily chemistry, and there is a history of mental illness in my family, just past Karma that needs to be dealt with

The central nervous system requires psychological health to perform normal functions.
We also have to be keen on what goes into our bodies! Our desiccated brain consists largely of fats (about 60%), the remainder being proteins, amino acids, micronutrients, and glucose. The bound lipids allow the brain's cohesion & oversee functionality. Omega 3,6, and 9 have been associated with the degradation of our intellectual capacity i.e. cognitive disorders, memory impairment, attention and concentration problems, and mood-related matters such as irritability and dramatic mood swings. Proteins advance the synthesis of amino acids, increasing the levels of tryptophan, tyrosine, histidine, etc and these trigger the production of a few important neurotransmitters and neuromodulators like dopamine and serotonin.
Hopefully there is salvageable information that stays relevant to your interests. Take it for a grain of salt if you will