Can anyone tell me if increasing from thyroxine 100 dosage to 125 how long before you would notice an improvement - if dosage is too high how long would it be before you become jittery and anxious. Currently on 100 and all results of blood test normal but through the day I feel so exhausted and then cannot sleep at night. Weight has started to increase as well as fluid retention. I am going to try adding an extra 25 to see if there is any improvement in symptoms although my GP would not agree to this. Maybe this is the wrong way to go about things and someone can advise me otherwise.