According to my shrink, who has no problem with me taking pre-generic Zyprexa, as long as tablets are kept dry, they're fine (I am, of course, assuming that these are not medications that you found in a damp box in the basement as part of an inheritance...) My late father, and two of my brothers (all MD's) concur with him.
Usually, if a med has gone bad, you can tell by a change in color, consistency, or odor (eg, aspirin that is no good smells like vinegar.)