I think US doctors have been slow to use hydroxyurea because they are comfortable with the system of transfusion and chelation. In addition, most of the long term studies on the drug's use in thal has been outside the western world. And of course, you're not going to have any big drug companies pushing for it, so it may be also a case of out of sight, out of mind. The results are also very hard to predict, so that may be another factor why doctors are hesitant.