Your use of "chemist" makes me think you're out of the US.
Most ADHD meds in the US are "controlled substances" and that means our doctors can only prescribe up to three months at a time. After three months we have to have a follow-up appointment, then they can prescribe three more months of meds.
Plus the federal government decided that too many people were taking medications like Adderall. So their "solution" was to instate a cap on how much Adderall manufacturers can make. Which means there's now a national shortage of Adderall. And that shortage means folks with ADHD are frequently going without their meds entirely or are forced to call multiple pharmacies in the area to ask who has their meds in stock. (My health insurance through work requires me to use a mail-order pharmacy because it means cost savings for them. But that means I don't have the luxury of shopping around different stores to see who has my meds in stock - at least, not to fill the prescription through insurance and get the lower price. So if the mail order place is out, then I'm screwed.)
Our healthcare system is so fucked.
I think state regulations might vary. Where I am, every three months I HAVE to have an appointment to get a refill prescription for my Adderall. But fortunately my psych is still doing virtual appointments, which is a lot less disruptive to my workday.