This book is deeply insulting to all those who live with ADHD symptoms; it is built around the notion that we would not have already tried a plethora of different approaches before resigning ourself to life on a drug saddled with judgement.
It is true that absolutely no immediate biological cause for ADHD has been pinpointed, but the same could be said for bipolar, depression, addiction, literally every mental illness in the world. Saul ignores the truth that humans simply don't know enough about neurobiology to label immediate causes yet. The chemical imbalance/ deficiency ideas that drive medication is merely a theory used to drive approaches of treatment- he briefly touches on that when he acknowledges that there are in fact some humans who seem to benefit from stimulants.
Of course the extremes of drugging normally energetic children and adults looking for uppers to enhance their work performance are real. Saul totally ignores the other negative extremes. He portrays it as if stimulants are readily available for anybody willing to sit through a doctors appointment. In my experience the opposite has been true. To mitigate the dangers Saul is worried about, it takes months and several alternate therapies after which doctors are willing to prescribe stimulants. Of course it varies by environment, but Saul practices medicine in an urban environment similar to mine.
I read this book with eager hopes of finding a way to live without adderall and was sorely disappointed. This book sells by stoking controversy against the current wave of medicine approach. It pretends to be holistic, but is actually extremely conservative in attitude. The few good points about ADHD and its' treatment that it makes are already common knowledge. I would recommend "Scattered Minds" by Dr. Gabor Maté for more nuanced assessment of the spectrum of behaviors described as ADHD.