Many people are unhappy with the position of their upper lip when they smile. In some patients who have overactivity of certain muscles, the upper lip overelevates when they smile and shows excessive gums (the "gummy smile").
There are two separate muscles (adjacent to each other) that are responsible for this overelevation of the lip: the levator labii superioris alaeque nasi and the alar nasalis muscles. The elevation tends to be symmetric although occasionally, one side elevates more than the other. In my opinion, the levator is the more dominant of the two muscles for this particular motion. This has implications for treatment location.
What are your options? There are surgical options, but they seem quite extreme. Some involve excision of excess gum tissue, and other attempt at repositioning the lip lower on the gumline. With the appropriate application of botulinum toxin, however, this can be prevented.
For this non-surgical treatment, a practitioner can use Botox, Dysport or Xeomin. A very small amount is injected to relax these small muscles. Undertreating the area is key, as if the practitioner injects too much, it could affect lip function (extremely rare). Having the patient smile during the examination allows the injector to feel where the muscle is on either side of the nostril. This area is then marked and injected with a single injection. Treatment costs are routinely under $100, and for effects that can create a subtle drop for 3-4 months at a time with no downtime and little risk, it just makes sense to try it out if you're interested.