MSM works and is a pain reliever also. One of the two types of glucosamine products is too large to be absorbed (don't have my notes so not sure which one it is).
Biotin is the best hoof supplement and the only thing repeatedly proven to work in scientific studies. But you have to give it in a high enough dose. Sillybunny is right about giving it time. It takes about a year for a horse's hoof to grow all the way down.