Is it acceptable to take an expired supplement?
In general, the answer to the question is a resounding no. The primary reason for the unequivocal nay is that once a supplement has gone several years past its date of manufacture, the potency of the ingredients decreases. Thanks to a process called oxidation–think of an apple turning brown once it’s peeled and exposed to oxygen-the ingredients may start to break down into unwanted metabolites. (For example, if L-glutamine has expired and is stored in a humid environment, it may start breaking down into glutamic acid and ammonia–not good.) Additionally, some ingredients–like liquids, oils and liquid capsules–break down faster than tablets.
Another key factor to consider about supplement breakdown is how the supplement has been stored and whether or not the product contains any preservatives. If a product is stored in a cool, dry place and left completely sealed, it may still be potent and effective. But again, degradation is dependent on the product: Sealed products like tablets (excluding essential fatty acids and fish oil tablets) might be OK after their expiration dates. Pure protein powders may also fit into this category. But if you want maximum potency, try to consume supplements as far away from their expiration date as possible-fresher is better.