Biotin?
I have taken it from day one. The hair loss starts about 3 or 4 months out and lasts up to 8 months. No one knows if biotin helps or not, no evidence either way. Most people have some form of it. Some loose more than others. There are some who don't have it. But taking biotin doesn't hurt anything. The nioxin shampoo is something I haven't used.
The theory behind the hair loss is that the body had a shock to it by the surgery or the rapid weight loss caused the shock. With the shock, the hair stops growing. When it starts again, it pushes out the old hair for new hair to start. There is the hair loss.