For adults, it’s under-diagnosed. Because some of the most common prescriptions for it are stimulants like Adderall, there is a fear that adults are trying to scam the doctor. Additionally, and imo even more infuriatingly, doctors are apprehensive about diagnosing an adult because “you made it this far in life without needing help. You can’t be ADHD/autistic/neurodivergent.” Fuck that mentality. I’m ADHD and autistic and I don’t need a doctor to validate me when they can’t even agree amongst themselves half the time.