Some doctors will only write the prescription for the exact dosage of the medication. My son's doctor told me to break his pills in half and see if he did well with a lower dosage. When we went back to see him, I told him the lower dose worked fine so he wrote the a new prescription for the lower dosage. He said that, ethically, he had to write it for the lower dosage for a 30 day supply. He considers writing it for a higher dosage and telling me to break them in half as insurance fraud. The 50 mg pills cost the same (out of pocket for me) as the 100 mg pills.