Though it may come as a surprise to the people who struggle to grow it at all, there are places where butterfly bush is invasive - so much so that Washington State and Oregon have both banned it from being sold or planted there. In response to this, plant breeders like Dr. Dennis Werner of NCSU have devoted their talents to developing non-invasive varieties that have the color, long-blooming, and butterfly-attracting ability of conventional butterfly bush but without the risk of spreading into the wild.
To qualify as a non-invasive variety, a butterfly bush must show less than 2% germination and derive from what's known as a wide cross. This means that the plant breeder takes two distinct species of Buddleia, only one of which may be the standard B. davidii, and makes a cross. This typically results in the offspring producing few to no seeds; it may also mean that the pollen is not viable from a plant fertility standpoint, so it also minimizes the risk of the non-invasive variety accidentally increasing seed set on any plants that have escaped to the wild.
If you are looking for non-invasive butterfly bushes, these are the varieties that currently qualify, and are approved for sale in Oregon and Washington (albeit under the name "summer lilac" to distinguish them from butterfly bushes).