I was treated both as a child and as an adult. After I quit my adult medication I was a wreck, and ended up going to therapy. It wasn't specifically to address ADHD, but just me in general. I took a break from work, began eating well, sleeping well, and exercising, and I feel like I've gotten a lot better at focusing. My diet became more or less low-carb, and I did strength training. Could those be it? I don't know, but I feel a lot better and am more professionally accomplished than I ever was. There's my anecdote.
QBC (quercitin/bromelain/vitamin c) seems to have a very good effect on my attention span, ability to concentrate, anxiety levels, etc. However it does not go well with coffee, I get a "speedy" feeling I don't like. So unfortunately I don't take this supplement as much as I would like, because I love coffee so much.
Other nutritional remedies can be found in "Prescription for Nutritional Healing" by Balch.
I was diagnosed with moderate ADHD, inattentive type, as a teenager and prescribed adderall. I was also quite depressed, but I hid that from my psychiatrist.
The adderall certainly helped me to focus, but the side effects were awful and I stopped taking it regularly. I’ve since been diagnosed with depression and started on sertraline (an SSRI), and very soon after noticed an improvement to my attention, ambition, and ability to complete tasks.
It’s not surprising, I guess, but near-constant thoughts of worthlessness/desire to die can make it quite difficult to focus on tasks and generally function.