All drugs lose their potency. Not past their expiration date, but everyday. Expiration dates are used as an indicator of when the drug has fallen 5% or 10% (I forgot the exact percentage) below the labeled strength. For instance, if your 10mg var expires today, then that means it's strength is likely 9mg (if 10% lost). Real pharma companies do not manufacture their drugs at exactly the indicated strength on the label. they typically increase the strength accounting for lost of potency from the time of manufacture to the time of sale to the customer. Don't know how BD formulates their drugs (well at least until they got shutdown).