It is illegal for a physician in the United States to use a non-FDA approved medication unless it is in clinical inestigation FDA-apporved studies. Revanesse is a hyaluronic acid, the properties of which. Unless FDA-approved and manufactured here in the United States, you really don't know what you're getting. If there are adulterants in a product to make it last longer, you might develop an immune reaction that could cause disfigurement.
Web reference: http://www.thenyac.com/restylane/index.html