I am not a doctor, so this info is from what I have read.
Starting dose should be a low doses, 15 mg to 30 mg, determined by health and in every case be individualized according to patient response and laboratory findings, with increments of 15 mg every 2 to 3 weeks. Adequate therapy usually results in normal TSH and T4 levels after 2 to 3 weeks of therapy. Readjustment of thyroid hormone dosage should be made within the first four weeks of therapy, after proper clinical and laboratory evaluations, including serum levels of T4, bound and free and TSH.
Hope this helps!