Methylcobalamin is extremely stable when it's dry, even at temperatures as high as 315°C / 600°F. However, an expiration date is required to be on all vitamins, so we stamp each vial with an expiration date of a little less than a year. This is the expiry date assuming you dissolve the B12 in saline immediately when you receive it. If you keep the vial in dry form, however, it will last for much longer.