I am taking letrozole and definitely noticed thinning, not as bad as hairloss from chemotherapy, but emotionally devastating to lose so much hair after it had grown back. My oncologist recommended Viviscal and warned me it world be at least three months before I'd notice a difference. She was right on both counts! By the third month I "thought" it was better. By the fourth month I "knew" it was. I continue to take one pill with breakfast and one with dinner and my hair is back to the quantity I had before cancer treatments.