Medication is a privilege that many with ADHD can't access. It also doesn't work for everyone. Are those people not disabled?
Also, ADHD is more than struggling to focus, or to sit still. Many of us struggle to start tasks, manage money, keep things tidy, or manage time. These issues can cause so many problems in life, ranging from inability to hold a job to relationship issues. Once the medication wears off, these symptoms rise back to the surface; because ADHD medication isn't a cure, it's symptom management.