There is no set timeline on how long a filler lasts. It all depends on how much is injected and the areas that are injected. If you put a very small (or too small) amount in, you won't get a good result and it will last a very short time.
What I see in most of these cases where people say it 'didn't last' is that they only had a small budget for fillers and wanted too many areas injected at the same time. If I have a patient with unrealistic expectations, I tell them to either do one area alone or, if necessary, save up to do more of a filler in the future so that the area is done in the right way.
Lastly, the skill of the injector is very important here. There are many new injectors who simply don't know what they are doing and how to do it. This means that they are injecting fillers in the wrong place and that can often result in very short length of activity.
It is so very important to go to a dermatologist or plastic surgeon who actually does their own injections. While they may have 'staff' who do injections reasonably well, the only way they are going to get skills that translate to good injections is to do it themselves and not pawn it off to someone.
