Fat injections are used when the patient wants to use their own tissues. We get fat from the hip area (using liposuction), process it, and then inject it into the lip, which gives a very soft look. Some think the fat doesn't 'last' but this is not entirely accurate. When done properly, some of the fat is reabsorbed, but a significant percentage is retained permanently. Because of this, we tend to 'over inject' knowing that in three to four weeks the final result will be closer to what the patient wants.
However, the lip is an area where I don't see fat grafting as the first choice because the lip moves a lot and it interferes with the take of the graft--the graft will not survive as well in the lips as it does in other areas of the body. For this reason, I actually prefer synthetic fillers in the lip, or a lip lift'. Lip augmentation can be performed in a very short amount of time, while under local anesthesia or sedation.
The lips are an important feature of your facial appearance. Anybody who wants fuller lips is a candidate for this procedure. If a patient has a long upper lip, she might want to consider a lip lift (in conjunction with the lip augmentation) for an overall rejuvenation of the lip. See my video for more detailed information about lip augmentation vs lip lift and the web reference for more detailed information about the permanence of fat injections.