The problem is it's not about the productivity, it's the clarity and it's profound for someone with ADD/ADHD. So I started abusing nicotine at a young age (a very common ADD self medication) and I quit several times over the years and every time I quite my mind would be in a fog and never come out. I am not talking about 5-30 days, I am talking about 5 years later and I wake up every day feeling foggy. I tried everything, and at some point I just relented to the fact that I must have obviously damaged my brain with nicotine, I did not really think about how clear the first cigarette made me until I took recreational Ephedrine as a teen. The funny part is for people with ADD they don't really get that coke speed out from speed, they just get really relaxed and clear, but there is an energy to the relaxed.
So fast-forward to my 20's and I pretty much had ignored that speed makes me clear, when I have some issues and the doc tells me I have ADD, and wants to put me on meds. I opted to not do it, and just kept on abusing nicotine.
Anyways, in my late 20's I have kids and decide they are not going to have a smoker for a dad, and quit cold turkey and that is where things went to crap. I could not focus on work, could not get stuff done around the house and the worse it got, the further behind I fell and it started to look like depression which is what can happen with ADD when you get overwhelmed by not being able to get started on anything. I went back to the doc, they put me on a low dose Meth Amphetamine and it's night and day. I don't think I could have ever quit nicotine if it where not for ADD meds.
Funny part is, I am not really into speed, the few I took in my 20's I never really liked, I don't do drugs but I am pretty sure if I did, I would be a heroin junkie as the few times I have had to have morphine or other opiates (medically) where quite pleasant. Point being the lack of desire for speed seems to be a common sentiment among those with ADD/ADHD