I don't know if they have. But I'd make a small bet that the chemical imbalance would also be put to right by smoking.
I have gathered a fair amount of anecdotal evidence over the years that people who have had attention problems did not have it, when they were smoked; or that people within a family who smoked could keep and maintain jobs, while people in the same families who did not smoke had troubles maintain employment. The difference seemed to be, still anecdotally, that the people who smoked could concentrate on their jobs.
Interestingly, the medicine I take, bupropion, is also used to help people stop smoking. I doubt any studies have or will be done along this line -- finding a benefit in smoking cigarettes being rather taboo at the moment. However, the implication is that there is something in bupropion that either is or replaces something in tobacco, that helps people concentrate.
In any case, we know of some chemicals that clearly affect mental processing. Ethanol (i.e., alcohol) is the best known. Caffeine is another. I'd have to check this, but I think there are studies that indicate that caffeine can improve mental reaction time. It is not unreasonable that there are other, lesser known chemicals, such as bupropion, that do as well.
As such, it may turn out that there is no such chemical imbalance that causes ADD, but that bupropion has an ability to enhance concentration. It may be that I was not sufficiently trained to concentrate as a child and that, as such, bupropion works as a mental crutch.
But in that case, we could apply that logic to at least some other psychiatric medications. Perhaps they do not correct imbalance, but, properly used, improve the operation of the brain.
In any case, one does not need to know how a match works in order to light a fire with one. We need merely observe the striking of one. Similarly, one does not need to know the specific workings of a medication in order to determine or, at least, have good reason to believe, that it does work.
By the way, I agree with you on marijuana.
“But in that case, we could apply that logic to at least some other psychiatric medications. Perhaps they do not correct imbalance, but, properly used, improve the operation of the brain.”
We know how some chemicals affect the brain, in the case of physiological problems with the brain, some drugs are moderately helpful. There are real chemical balances too, especially hormonal, and they cause severely bad feelings, but they are physiological also. As far as I know, all psychosomatic drugs, even mild sedatives are deleterious to the brain, and none are beneficial to any of its functions.
http://theautonomist.com/home/?/autonomist/article/psychiatric_drugs/
On the other hand, whatever substance an individual finds useful or helpful, nicotine, alcohol, or psychosomatic drugs, they ought to be free to use them. I am very much opposed to both forced administration of drugs as well as the forced prevention of their use.
Hank