Worse than that. Even relatively weak solutions of salicylic acid can cause gastric bleeding after a relatively few doses. Gastric bleeding can be a medical emergency – especially aspirin-induced, since aspirin inhibits the platelet clotting pathways. That’s why willow tea, known by pre-Roman Druids as an analgesic , was avoided by Roman physicians (“salicylic” acid comes from “salyx”, Latin for “willow”)
While a single dose of a slightly out of date aspirin for a headache may only give you a sore belly, Stale aspirin is more likely to be taken by heavy users in serious pain (e.g. gout, arthitis) with may only respond to larger than OTC doses and longer term use. I’ve known severe arthritics who tke 6-8 tablets with each meal because “nothing else works”. Though high-dose aspirin is not a mainline treatment for gout anymore, I mention it for two reasons: a) low dose aspirin actually increases uric acid levels, often making the gout worse, while very high doses can cause the body to "dump’ uric acid; and b) the Roman citizens had a tendency to “saturnine gout” due to lead contamination from their newfangled “plumbing” (plumbium is Latin for “lead”) plus high consumption of alcoholic products (which aggravate gout, and were often lead contaminated to boot) – so Roman docs saw many cases of death in mere days from willow preparations.
In fact, that is the whole point of aspirin: a chemist at the Bayer company found that tacking an acetyl group onto salicylic acid created a compound that was much less irritating to the stomach, but it would break off, safely, when pancreatic juices neutralized the stomach acid, in the duodenum. When you take vinegary aspirin, you’re going olde skoole, and not in a good way. That vinegar is formed when the protective acetyl group combines with water.
While I’d never advise anyone, professionally, to take expired meds, I have taken (not very) out-of-date OTC meds. The problem is: I have some idea idea of which ones to avoid, and what to look for. Most people won’t. I’d avoid vinegary aspirin even if it wasn’t expired (due to e.g. poor storage), but many laymen would take it if it was “in date” – especially once it is removed from the bottle. An aired-out tablet may not have a strong smell, but the bottle quickly does.
This isn’t medical advice. You’re much too smart to take medical advice from a stranger on an Internet BBS, right?