Auerbach's excellent books Wilderness Medicine and Field Guide to Wilderness have an appendix entitled Drug Stability Information. The initial sentence is: "Stability data on drug products are derived from studies don in controlled enivormnmental conditions."

A typical use-at-your-risk disclaimer follows, for instance, at the end of the acetaminophen listing: "...Avoid freezing. Stability after freezing is unknown."

Assessments for each listing are quite conservative, and would seem to be based more on appropriate caution because so little cold-weather testing has been done, and therefore there is little real data on which to make recommendations.

It should go without saying that the pharmaceutical manufacturers and sellers have a clear vested interest in selling more product rather than less. The previously mentioned Air Force study is a clear example of most drugs being useful far beyond their printed "expiration date." It's not clear to me what the storage conditions were for the Air Force study; if anything cold weather storage/freezing conditions should make medicines last longer. Pills, capsules, and powders at least, contain essentially no water, so there should be no freeze-thaw cycle concerns as with freshly frozen food-stuffs. Many meds in syrup form are alcohol based, so have their own anti-freeze built in, to survive the low temperatures without freezing most of us have to deal with.

I'll restate an important point. With the exception of tetracycline only, which may degrade into a substance toxic to the kidneys, what happens at some point is loss of potency. There appears to no evidence that you're going to poison yourself by using 6 year old Tylenol or Advil.

I typically use prescription and OTC meds for several years beyond their expiration dates (the exception would be outdated tetracycline); the listed dates are in the drug companies and re-sellers best interests, not mine. I'm willing to wait to see published evidence of harm.

Further research on this would be of interest, and inexpensive to do. I don't think industry funding for it, however, would likely be forthcoming.