Is it true or a myth that expired tetracyclines are toxic? are there some studies or just one paper from 50 years ago? any good, modern data about it?

I have not heard thi: Many meds have expiration dates that are purely a marketing tool to get the patient to throw away the meds and but more. . Otherwise the manufacturers would not have to make so many to fill the need of filling garbage cans with "dated " pills. Really old pills are probably not a good idea and especially if they have not been stored properly.