I was diagnosed ADHD in college when a friend who was recently diagnosed told me I had it too. I went to a specialist and he said diet was a big factor and bad dietary habits can greatly exacerbate symptoms or even cause ADHD symptoms in people that are not really ADHD. I was in college so naturally I didn't listen to him, and I started taking Dexedrine that he prescribed. It helped a lot at times, and I took it through college. I still was pretty miserable at college though.
Right after college I co-founded a startup. I was looking for a way to avoid joining "the real world" of working people. I stopped taking the meds and was basically just hyperfocusing all the time. That first year there was only 8 total days I didn't go into the office to work (including weekends and holidays). I was able to use the hyperfocusing because I didn't have a family and didn't feel like I needed a life. That company was bought and a few years later I started another and went through the hyperfocusing stage again. I didn't even sleep in a regular cycle, I would stay up for 20-24 hours and then sleep 4-8. I was a mess, but it didn't matter.
Years later I now have a family and those habits won't fly. I have always remembered the advice my doctor gave me now 24 years ago, but it was only the past 6-8 years or so that I actually started applying it. It works very well in my case, but I know my case is not extreme.
I need to avoid carbs during the day. I need to get a good night's sleep. If I eat a salad at lunch I do not have attention issues. I now do low carb almost all the time and it has changed my life.
Do I actually have ADHD? Yes, I think so. But it's not an extreme case, and I find it to be pretty well managed with good diet and sleep habits. Exercise helps a lot too. Always try this route before drugs. It's not a silver bullet, but I believe it can help a lot of people that might otherwise look to medication to solve their ADHD problems in themselves or their children.