There's no good evidence that ADHD is not the result of psychological conditioning. For that matter, even if you measured abnormal neurotransmitter activity or brain scans in suspected ADHD patients before diagnosing them, if you looked at animal psychology studies where pathological behavior has been induced by conditioning, I'd be surprised if there weren't abnormal brain scans and neurotransmitter activity there, too. The neurochemical/neurophysical measurements that might provide "evidence" of a non-psychological etiology are invalid if those physical aspects of the brain are themselves affected/modulated by neurological conditioning/development.
If your solution to any problematic "neurobiological" symptom that responds well to a certain drug is to prescribe that drug, because if it responds to a drug it must be a chemical/genetic problem, then everyone will be on a drug eventually. Probably several.
1) You don't need to speculate what neurobiological means using phonetics, it's a real word with a definition you can just look up if your actual interest is in the facts. Neurobiological actually means related to the nervous system of the body. ALS is also neurobiological, and I'm guessing you wouldn't say it "sounds" psychological.
2)If you'd bothered to look, you'd find there is actually quite a bit of study of D2 and D4 availability correlated with ADHD symptoms. Like virtually all medical diagnoses both psychological and physiological, differential diagnosis is done by combining probabilities with presented symptoms, and not with exhaustive testing. Your requirement of diagnosing ADHD with a brain MRI is the equivalent of requiring endoscopy to diagnose an ulcer.
So what you say is factually incorrect, there's plenty of evidence. That's why the scientific body of many countries including the US has classified it as neurobiological (not psychological) for years, and the bulk of the scientific community believes pharmaceutical treatment is necessary in the same way that a broken arm needs to actually be set instead of telling the patient not to be lazy.
If you want to use scare quotes and insist on unfalsifiable assertions "prove the negative 'not' the result of psychological conditioning" then you are placing your argument in the same category as climate change deniers and anti-vaccers - anti-science, anti-rigor, pro-scare quotes.
Secondly, even if you are convinced that these correlates are causal, if you do not actually test for them, then you have to show that the diagnosis method correlates strongly with the biology. I have bothered to look. I can't find such data. Are you saying you have?
The last part of what you are saying seems to be combination of an appeal to authority and affirming the consequent: "Because the scientific community currently recommends pharmaceutical treatment, the problem must have an organic cause."
Having worked closely with psychiatrists, I can assure you that recommending a pharmaceutical treatment is rarely done because they understand the mechanism of action. It is rarely even done because they think the cause is organic rather than environmental. It is done because it is the only effective option available to them.
Psychiatrists don't have the power to change schools or parenting, but they can prescribe drugs which may improve the outcome, and so have a duty to do so. This doesn't mean that the problem is a lack of medication, or even that the cause is biological. It's that doctors can't change the environment.
Consider PTSD - which can be treated using drugs and therapy, and clearly has neurobiological correlates. The cause is war and violence, not the lack of drugs.
Is there similar literature for ADHD?
To my understanding, they are not, which makes ADHD a psychological condition.
