I did a search but all I came up with was steroid shelf lifes. Anyways simple question. How long after opening are most vitamins still useful? I’m assuming they will lose potency slowly. Possibly through oxidation but I’m wondering. I have a few bottles that I’ve opened up and haven’t finished in quit sometime and I’m curious if there is a point to keeping them? What about M and ZMA? What about Glucosamine? Thanks. Ciao. 
???
So no one knows? 
Most of the time, OTC drugs (e.g. ibuprofen) are dated to give the impression that they expire much sooner than they really do. This is obviously a way of increasing sales.