You can only buy packets of 16 at a time. This was a shange introduced by the government in around 1998 or so. The other option was to make all paracetamol contain methionine or N-acetyl cysteine, but that would mean that they didn't taste (or is it smell?) very nice and would've pushed the price up, so they went for the small packet size. I don't know why there isn't a license for huge bottles of paracetamol containing methionine if people want to have it, but there you go. In many shops they won't let you buy enough paracetamol to be a risk. As one of the other commenters mentioned, it gets flagged up in barcodes so that all the paracetmol you're buying (even inadvertently) gets added up. Boots, which is the UK's #1 chain of pharmacists, is very strict about this. Last year when I had a broken arm and didn't want to have to keep nipping to the chemists to keep myself dosed up I wasn't allowed to buy too many packets together. I tried to argue that I was hardly a suicide risk, but they wouldn't even let me split it up into two purchases. It was a bit annoying, but very professional of them.