I found this response to the question on BB.com if it helps.
Creatine Monohydrate is considered a nutritional supplement, and is therefore a chemical which alters over time with exposure to heat, light, etc. I'm not really sure how the "expiration date" is established by manufacturers when it comes to supplements, but there are surely some standards used in order to label their products with a maximum shelf life.
I would think that if you've kept your container of Creatine in a cool, dry, light deprived environment, its bio-activity is likely still viable. I'm going to guess that a big part of establishing shelf life for products is to perhaps take into account a consumer not subjecting the product to optimal storage. Probably somewhere in the middle of the road is where it's likely assumed consumers will take advantage of most advantageous storage conditions.
Then on top of this, just like with drugs and other food items, the FDA probably has a say on the standards, and just as an added measure of safety, a time limit is established so as to avoid any possible toxicity or bacterial contamination.
I'm NOT going to outright tell you to use the container of Creatine, but I will say that if you HAVE kept it in accordance with the cool and dry conditions I've mentioned, then it probably won't kill you to ingest it. I DO say though, "user beware". If you have ANY reservations about it at all, based on appearance, odd smell or any other negative observations, then you'll be better off to just toss it and buy a new container.
But if it still looks and smells like it did when you first purchased it, it's likely it's still viable and will act the same way in the body. Do keep in mind though, no matter how well you store this
substance, it WILL over time evolve and degrade which will alter its original integrity and thereby render the substance useless. Keep in mind, one can never be too safe in these matters.
