I've been on letrozole for 5 1/2 years and have found no difference with brands. The active ingredient is the same and the only difference between brands would be fillers, binders and possibly colourings. Unless you are allergic to say lactose which has been used as a filler or tartrazine, (E102), a yellow food colouring, there shouldn't be a problem. I take whichever brand my pharmacy has on the day, at the moment I have the Pharmacor Letrozole but have had quite a few over the years.