The general rule of thumb on expiration dating: Vitamins and herbs lose potency pretty quickly. Standard industry policy is to load most vitamins with higher dosages up front (up to 20% higher) so they last the full length of the expiration date. Beyond expiration vitamins and herbs will degrade and start to lose their potency. However, they should still be safe if stored properly. Dairy proteins change in taste over extended time when their fats are exposed to light or oxidation but protein value should last beyond most expiration dates. Enzyme action can cause a breakdown of the protein as well. Most amino acids will last beyond their expiration date when stored properly, kept out of high heat, light, and moisture. Creatine should be fine if sealed and kept moisture free. Some side information: Adding an expiration date or best used by date to a dietary supplement is voluntary according to the regulations. However, if the manufacturer does add them, they must first substantiate the expiration through scientific validation, usually accomplished by an accelerated stability test.