Agreed - medications like birth control simply wear off (which is pretty bad, when you think about it). Others, such as tetracyclines, actually become toxic. Hydrocodone is a codeine/acetominophen formulation. The codeine part simply becomes ineffective, but the acetominophen part becomes acidic and can cause GI problems.
Quote from zuzu8:MIKEL-
Expired drugs lose potency, and are probably completely ineffective after 3 years.
However, they CAN degenerate into substances which are seriously harmful to you. Chemically, I don't know what happens to hydrocodonewhen it breaks down, but it may be a risk you might not want to fool around with.