If you’re on special meds, re-order the first chance you get, and keep doing that each time. You’ll start building up a supply of them, in case the source is disrupted at some point in future. Even though most meds in pill form have a one year shelf life. They’ll last longer, just may not be as effective. You can do the same thing with those as with foods; first in, first out.
That's on the short side. Testing done by the DoD and FDA have shown that all most all medication, if kept in a cool, dry environment, have 90% efficacy after 10 years.
I’m all for pre-stocking meds, but the method of ordering refills as soon as the pharmacy will dispense them won’t always work. Some plans will count the doses dispensed over a period of time and then put a hold on the prescription. But it doesn’t hurt to try and one could accumulate a few weeks supply that way anyway.
I have been ordering cheap generics from overseas for this purpose. I do take them occasionally when I run out of the prescription and to test, and the only deficiency I’ve noticed is that the extended release mechanism is not quite as effective, but it could be a matter of these particular drugs/manufacturers. Recently ordered 600 doses of a drug for the same price as 50 cost at a local pharmacy. I have had good luck with the Indian pharmaceutical manufacturers.
Regardless of how you obtain them, Rare would it be that the usable shelf life is going to be less than five to ten years when stored in cool, dry conditions (except for known perishable stuff). Even rarer is a medication that actually becomes toxic past its usable life (e.g. tetracycline).
I took some some 12 year old hydrocodone a few weeks ago from an old dental prescription and it still worked, but maybe a little less potently. Many, many times I have taken prescription drugs five years old or so that still worked fine. Depending on the type of drug it might not be so easy to determine its potency, but in the vast majority of cases a few years cool storage will make next to no difference in efficacy.