As scary as it can seem to be losing hair when you want to be growing it. This is actually a good sign. For a small percentage of people, new treatment stimulates the hair follicles. This provides further nourishment and encourages regrowth. These new hairs start to grow, and they push out the old thinning hairs, which is why you may start to lose more hair than normal. This shedding stage does not happen to everyone, however, when it does, it can last between two and four weeks.