A psychologist or ADHD specialist is who would typically diagnose ADHD, through an evaluation. While it’s perfectly legal for a GP to prescribe ADHD medication, you do really want someone with experience with ADHD medications managing your treatment.
Getting off ADHD meds by 30’s is nonsense, by the way. That’s old-school thinking that ADHD is really only a disorder for children, which isn’t the case — it’s a lifetime disorder.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism