The standard best practice for ADHD medication is to start at the lowest dose and increase only if and when needed. The doctor who prescribed 20 mg starting out should not be treating patients with ADHD because he/she has no knowledge on the subject, not even the general best practice.
ADHD medication dosage isn’t based on age or size like most medications. ADHD stimulant effectiveness depends on metabolism, genetics, and the individual’s neurotransmitter needs. A 40 lb 4-yr-old could need a max dose and a 200 lb adult could only tolerate the lowest dose. It’s all very individualized.
Glad to see you’re going to a specialist.
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism