I'm sure if you wanted to buy 10 boxes of it, they'd be quite suspicious

They definitely are. I was born with major sinus issues, and my doctor had me on an abnormally high dose of pseudoephedrine all throughout my teenage years to treat some of the symptoms.

As a kid, my mom would take me to the pharmacy to fill my prescriptions, and I guess the sight of a mother with her stuffy red-nosed child wasn't very suspicious to the pharmacist. But when I got older and would go to the pharmacy myself, I would often end up going home empty-handed with my prescription unfilled, because the pharmacist would see a scruffy teenager trying to buy a few boxes of something that can be used to make meth, and just refuse to give me any of it despite having a prescription on file for years.

Even when I was allowed to buy it, I could never buy more than a month's worth at a time, and it had to be when I was about to run out, otherwise they'd tell me I needed to come back in a few days. Led to a lot of "sorry, I can't go on that camping trip because I need to renew my prescription during those specific days or I won't be able to breathe for half the trip"

I wish the alternatives worked, because I would have much rather used them.