US as well. I have ADHD family members and literally every time the script comes up for refill it’s delayed due to inability to get the medication. Doesn’t matter if it’s big national chain pharmacies or (if you can find one) a local pharmacy. It’s bullshit, stressful, and frustrating…try not hyperfocusing on knowing you may not be able to get your meds that help you not hyperfocus as an ADHD sufferer.
My wife is the same. She calls a few days before the script is up to see if they can fill it. If not then she calls around neighboring pharmacies to see if they have it available and if they do has to contact her med manager to get it transferred. It's a huge PITA but she's only missed a day or two thanks to keeping on top of it. It seems like the different chains and grocery stores are on different delivery schedules so someone usually has just gotten some in.
She is lucky she can even do that. If it were an opioid they would just be like "no". At least that was the case for my aunt before she passed. She just would have to wait in pain until it was available. I think it's up to the pharmacy if they will accept it or not, and in the best cases they would politely just say "we can't do that", some pharmacy techs would directly accuse her of trying to pharmacy shop to get a script fill duplicated. Luckily it didn't happen often, I think when it did it was because there are now DEA stock limits, so it can take a while before the next order comes.