Juvederm enhancent of lips is only temporary. Like a haircut, the lips will return to where they were over time. Hyaluronidase can be used to dissolve the filler if you are unhappy.
The effects, wanted or unwanted, from Juvederm last typically 6-12 months. In my experience, dynamic areas such as the lips are areas will Juvederm tends to last the shortest and may even be less than 6 months.