Can vitamins and powder expire?

I have B-12 vitamins that expire this month. Do they really go bad or is that their shelf life?... Same with protein poweder, it went bad in September 08.. shelf life? or expired?..Can vitamins and powder expire?
i cant say anything about the vitamins, but I know for a fact that the protein powders are good up to 2 years after their shelf date expiration, although the taste slowly gets worseCan vitamins and powder expire?
In my personal experience, I took expired vitamins and got violently ill, and I didn't know why, so I kept taking them and kept getting sick for a month. Stupid I know, but it's good you checked the label and asked this question, so maybe you won't have to go through what I went through. Throw them out, buy fresh ones.
I would gestimate a true expiration date of 2-3 months post what it says on the bottle for most things perishable. Most things just loose potency which other expired things turn into something harmful. I think you purchase new items
Yes, they can.