Both Restylane and Juvederm manufacturers do not recommend re-using syringes for future treatments.
Some physicians re-use the syringes after use for the next several months. It is one of the off-label uses of these products.
Off-label treatments, while not FDA approved for a particular indication, are used for many different products, and it usually means they haven't been studied enough for this off-label use. Usually the product has been studied and is approved for other uses. For example, use of Restylane in nasolabial folds is approved and recommended, and the use of Restylane in the lips is off-label. Despite that, many physicians successfully and safely use Restylane in the lips.
The reason for re-using the syringe is, most of the time, just saving money for the patient. Considering how expensive the product is and the price per treatment, some physicians offer to save the product if there is any left. It is usually safe to do. The alternative would be to charge the patient for a new syringe every time, which is certainly an option and some clinics prefer to do it.
All that being said, Juvederm usually does not hold very well after it is opened, and tends to dry out quickly, so we prefer to use the whole syringe and not save it for future use.
