Goserelin-induced transient thyrotoxicosis in a hypothyroid woman on L-thyroxine replacement.

An increase in free thyroxine (fT4) and a decrease in thyroid-stimulating hormone (TSH) was observed in a hypothyroid woman on levothyroxine treatment after implantation of goserelin, a gonadotropin-releasing hormone (GnRH) analogue. In the literature no data are available that describe a drug interaction between GnRH analogues and thyroid hormone replacement. Our hypothesis to explain this observation is that goserelin decreased serum thyroxine-binding-globulin (TBG), resulting in an increase in fT4 and thereby a decrease in serum TSH.