> Most medicines are sold in blister packs these days. Won't that prevent a fair bit of the environmental stress from affecting them?

Well, it keeps out humidity, and might prevent air-exposure effects. It won't prevent heat effects and some other environmental effects.

Also, quite a lot are sold in bottles of pills or other non-blister-pack forms.

I live in France and cannot remember the last time I saw pills not in a blister pack.

I remember vaguely having seen pills in bottles maybe 20 or 30 years ago. Again this is for France, I know that e.g. in the US one gets refills.

Which by the way I find great because the waste of pills is tremendous. It would have been much better to get the specific number prescribed.

It is a waste of pills- but in many cases the marginal production cost of a pill is incredibly small. See generic asprin, many hundreds of pills for a few dollars at an ordinary grocery store. More than you need, but the packaging & marketing probably still costs more than the pills.

Over here, benadryl is the main over-the-counter drug I see in blister packs. They say it's to slow down the meth cookers.

I think you mean Sudafed. Sudafed is pseudophedrin, which is a great decongestant and used to make meth. In most states, you have to go up to the counter and ask for it, as well as supply ID and sign a form promising not to do anything illegal with it. Benadryl is diphenhydramine, which is just an antihistamine, and you can totally get in bottles (in the states). I tend to always have both on hand in case of an allergy attack. Granted, I'm more likely to reach for the Sudafed than the Benadryl. Benadryl has the side effect of intense drowsiness (I guess you can't sneeze if you're in a coma). I also buy a year's supply of Zyrtec and benadryl at Costco. It might seem like a "waste" but when you suffer from bad allergies, it really isn't.

I'm a long time pollen allergy sufferer living in the hell that is South Florida. I know my allergy meds.

That's not the reason. Benadryl being in blister packs long predates its use in meth cooking, like by 30 years. The real reason is more likely marketing. If they sold them in a bottle, the amount they charge for those few tiny pills would seem outrageous. A blister pack gives the packaging more volume.

This varies quite a bit throughout the world (I think). I've had both blisters and bottles in New Zealand/Australia.

Yeah, I think USA is atypical for bottles. I was surprised to see bottles of 1000 Tylenol* tablets at the CVS chain.

In Australia the only thing in bottles are vitamins and similar, though it is possible to get small bottles.

* acetaminophen / paracetamol

Most medications at the patient-level are in amber vials in the US (all pills loose). BUT there are still plenty of meds still further up the supply chain that are in tamper-evident packaging and could be donated if short-dated.