Collagen injections have largely been replaced by Hyaluronic Acids such as Restylane, Juvederm. The reason for this is that hyaluronic acids last longer. Collagen lasts 3-6 months and the hyaluronic acids can last from 6months to a year. This has been proven in head to head studies comparing them. Also, collagen injections usually require a skin test and time to wait for the results. There are some collagen injectables that don't require a skin test and they have gained some popularity but not as much as hyaluronic acids. Importantly, you should go to someone who knows aesthetics and facial beauty. This will avoid results like the Octa-Mom, Meg Ryan, Heidi from the Hills, Lindsay Lohan, Brittany Murphy, etc. The reason for this is that our understanding of aesthetics is not solid at this point. We really don't know how large the upper and lower lip should be.