I believe that the vast majority of physicians, both dermatologists and plastic surgeons, now use hyaluronic acid fillers ( Restylane, Juvederm) for the lip itself. Back in the day, some of us, including myself, were using collagen de define the border, especially the Cupid Bow area, into something called the Paris Lip. Some physicians ( in those more halcyon  days companies only marketed their products to dermatologists and plastic surgeons) began to inject collagen into the lips directly. However, some of our eagerness was tempered by the FDA who promulgated that we were not to inject into the lip itself. 

   Lip augmentation fell out of favor until its renaissance with the hyaluronic fillers. Many of  us, including myself, will often use Cosmoderm, a collagen filler around the lip. It seems to give beter definitiion and is firmer than HA fillers. But few inject collagen into the lip itself anymore. 

    Good technique on the part of your physician will give a very natural appearance and should not look fake at all. You may occasionally see some pretty ludicrous looking lips, especially if  you peruse National Enquirer. But the sausage lips, duck bill lips, etc. look  of the past seems to be fading. Thank God.