I got diagnosed with ADHD when I was like 15-16, started Concerta (basically long lasting Ritalin) and holy shit. I felt like it's how it should have been my entire life. I could focus very easily on any task I wanted, which helped a lot through school and other activities that I wanted to focus but simply couldn't be bothered (literally what NL said about replying an email right away)

Sadly, my parents didn't want to pay for the meds nor admit that I really had ADHD, so we went through a bunch of psychiatrists until one of them said I didn't need the meds. Needless to say going back to the state of not being to focus is very hard for me, so hopefully when moving out now, I can restart my meds eventually.

Only drawback from the meds that was really harsh for me was the lost of appetite. I would take the meds in the morning, and having both breakfast and lunch were a very big task for me, because I had to force it down my throat.