Hi, I also noticed hair loss while on rebif (started on it in fall 2006) Both in quantity of hair coming out in hairbrush, amount coming out in shower when washing hair, and loss of volume. I was hospitalized with some infections in April 2012 and Drs. treating that recommended going off rebif, which I did, and I can tell hair is growing back. I just started back on rebif, and prior to that did consult a dermatologist who recommended 5,000 mcg biotin per day and use of men's rogaine, as he said women's didn't have enough strength. Also, prior to the hospital stay I was on Rainbow Light Nail Hair and Skin which did have 2 mg of biotin. This was something else the hospital Drs. had me stop taking, and I did have nail splitting, which stopped after my family Dr. ok'd going back on the supplement. Now I will just have to see if the larger amount of biotin and rogaione counter the rebif hair loss. Perhaps hair loss isn't that rare of a side effect?