Based on Ray's writings about caffeine being a surrogate for thyroid hormone, this study showed that caffeine suppresses both TSH and growth hormone (GH). Ingestion of Cynoplus or other equivalent product containing both T4 and T3 has been shown to have the same effects. The effective human dosages were 300mg-400mg caffeine for TSH suppression and 500mg-600mg for GH suppression.
http://www.ncbi.nlm.nih.gov/pubmed/6104718
"...Caffeine lowered serum TSH and GH in a dose-dependent manner with ED50 values of 30 and approximately 50 mg/kg, respectively. TSH levels were depressed 1 to 6 hr after injection and correlated with serum caffeine levels greater than 20 micrograms/ml. The decrease in serum TSH was followed by decreases in serum 3,3',5-triiodothyroxine and thyroxine 4 hr after caffeine administration. Theophylline and theobromine had effects similar to those of caffeine on hormone levels."
http://www.ncbi.nlm.nih.gov/pubmed/6104718
"...Caffeine lowered serum TSH and GH in a dose-dependent manner with ED50 values of 30 and approximately 50 mg/kg, respectively. TSH levels were depressed 1 to 6 hr after injection and correlated with serum caffeine levels greater than 20 micrograms/ml. The decrease in serum TSH was followed by decreases in serum 3,3',5-triiodothyroxine and thyroxine 4 hr after caffeine administration. Theophylline and theobromine had effects similar to those of caffeine on hormone levels."