Over-the-counter

I'm only guessing here but it might be from being able to get these drugs by just handing your money over the counter as opposed to having to see a doctor and get a prescription.

'off the shelf' actually conveys the meaning that a product has not been tailored to a specific individual or situation. For example you can by an 'off the shelf' accountancy package like MYOB (Make Your Own Business) or you can pay a company to write and develop a package unique to your needs that can't just be purchased from a retail shop. Another example would be a 'off the shelf' suit as opposed to a tailored one.

A further distinction is also made between "Over-the-counter" (OTC) drugs and "behind the counter" drugs - behind the counter drugs being drugs that the pharmacist can sell at his discretion, but can not display or advertise.

As someone mentioned earlier, back in the day. all non-prescription medications were kept behind the counter. Those that were legally sold to all askers were handed "over-the-counter." Those which were more illicit were handed "under-the-counter," which was akin to "under-the-table"

This is an example of where the language is lagging behind the mercantile world

I am a native speaker of American, which is not at all the same as a native speaker of English, British or any of those other things like Australian.

When I was a child in the 1950s, there were no large chain pharmacies or drug stores, such as RiteAid. The drug store was owned by a licensed pharmacist. There were some national brands of remedies (such as Exedrin). These were kept behind the pharmacist's counter, and you asked for them, as opposed to the other goods such as toothpaste which were on the shelf.

Drug language can get to be confusing. There are "controlled substances" (such as morphine which has both a legitimate medicinal use and a recreation, or illegitimate use). There are "proprietary drugs" and "generic drugs". Proprietary means a specific formulation; generic means the same drug without the brand name, and possibly some other features that make it work better.

I wouldn't use "off the shelf" to talk about drugs; I would use it to talk about a generic solution to a specific problem.

And contrary to what Jay Frankenberger thought, the role of the pharmacist in health care has plummetted in esteem and status.

Over the counter has traditionally been referred to as products that are kept behind the counter for various reasons' such as frequency of theft, age related reasons (minors) or because it is felt that counseling is appropriate. For many years products such as prophylactics were sold over the counter to discourage minors and adults from stealing. Many non-prescription cough syrups were sold over the counter to discourage them from being bought and abused by minors. Cigarettes have traditionally been over-the-counter items even though they don't require a prescription.