In july my ths was 1.54 ,in august 0.14 on dosage of 137 mcg synthroid (thyroxine).t4 free 37pmol/l thyroid cancer no rai i dont'n know what cause this big change?

Actually: in the "low" TSH "range" there is not a lot of difference in those values. You indicate that thyroid medication is being given for a thyroid cancer of some kind and that RAI has not been given. I therefore "assume that your Physician (?Endocrinologist) is trying to SURPRESS your TSH (thus the 0.14 is BETTER than the 1.54 readings!! SO IT'S NOT REALLY A "BIG CHANGE " and in fact is BETTER..!!! Z