Sorry to continue the over-the-counter foam, but I looked it up, and in the UK there are 3 classifications for medicines for sale:
1) 'POM': Prescription only medicine.
2) 'P': Pharmacy medicines, sales of which need Pharmacist supervision and
3) 'GSL': General sales list, which you can buy in a corner shop / petrol station for example, needing no medical supervision.
Both 2 & 3 are technically OTC, which is everything except prescription drugs (source: http://www.pagb.co.uk/regulatory/access.html
). However, colloquially, I think the general usage is that "P" drugs are called OTC because they are kept behind the counter and handed to you over it, whereas "GSL" are available in many places.
This is incorrect usage, I think, as OTC actually means, as someone says above, on the consumer side of the counter.
I was talking about 2) medicines, classed as 'P', where no ID is required but you are asked questions about medical history and other current drug usage. I was using OTC to mean passed over the counter, incorrectly, but in the current lexicon.
In the US it doesn't look as though there is this classification of 'P' - it's either prescribed, or available to purchase without medical supervision. The restrictions on pseudoephedrine, requiring ID, are to control sale to limit meth production, not because of concerns about patient usage (which is the reason for the P classification). /foam