They should not need to prove anything but safety. If it doesn't work, people won't buy it past the first try.

I recently got an Rx for a nonsteroidal antiinflametory gel. It works great, and does not have the bad and potentially dangeours side stomach side effects (probalby not the bad heart effects either) but is expensive. There is no reason to believe that Ibuprofen would not work well as a topical.