How long the effects of dermal fillers will last depends on the type of the product, the area of treatment, and the patient. Hyaluronic acid fillers tend to last shorter; however, they are reversible if you do not like the results or you have side effects. These will typically last from 6 to 18 months. Injections to the lips will wear out a little faster.
Synthetic fillers tend to last longer, as they are not absorbed by the body. They can be a good option for the right patient, but results last for several years and can not be reversed if you do not like the results or show some side effects.