Growth hormone secreting pituitary adenomas(GHomas) produce excessive GH, stimulating excessive insulin like growth factor 1(IGF-1) synthesis in the liver, thus causing multiple systemic complications. The life expectancy of patients with untreated GHomas is shortened by ten years. The treatment goal of GHomas is to shrink the tumor volume and normalize GH and IGF-1. Under current treatment, only 50-70% of patients get remission. Rosiglitazone is a widely used oral antidiabetic medicine. The investigator's preliminary data showed that rosiglitazone decreased the synthesis of GH and IGF-1 in rat pituitary tumor cells GH3 and hepatocytes respectively. The investigator plan to investigate the efficacy of rosiglitazone in the treatment of patients with GHomas who have not been alleviated by other therapies.