I would never tell anyone to avoid medication (it’s not for me to diagnose, prescribe or advise, especially to strangers on the internet), but in my own ADHD experience, I’ve managed without them.
I created an ADHD management system based on what’s worked for me. It’s very much like what commenter Stephen described: Physical activity, routine, proper nutritional intake in which consumption of good fats and avoidance of sugar are crucial. Since my partner went on the keto diet for his own health issues, I’m pretty much entirely on the keto diet now too, but my diet has been “keto-ish” for a couple of decades.
Adequate rest/downtime is important too.
A lot of people default to meds without considering lifestyle changes, but not everyone needs them. Some people might. Again, I’d never tell anyone not to medicate. I think that prescribing treatment to strangers on the internet without knowing anything about the person is irresponsible and potentially harmful, and I cringe when I see people on internet forums ask for specific health advice.
This is what’s worked for me, though. Once I implemented dietary changes, my ADHD improved significantly within a couple of months. I still have days when it flares up, but then I look at what’s going on in my life, how I’ve been eating, how I’ve been sleeping, etc., and I adjust.