There is one filler that lasts perhaps two years, but it requires a series of monthly injections, typically four to five, to gradually build up the fullness.
Also of note is that many of the products are a form of "hyaluronic acid," which is a normal body substance. These particular fillers can be made to dissolve away in the unlikely event that someone develops excessive lumpiness at the injection site. Although I've never had to do that, it's nice to have such a safety net, and I tend to prefer using them at a patient's first treatment. Side effects are almost always limited to lumpiness and bruising. Very rare is the risk of scarring from inadvertent injection into a blood vessel.