Human growth hormone in reasonable doses is always safe. (hgh10.com)
If clinical signs of hypothyroidism remain despite the use of reasonable doses of thyroid hormone, the following must be considered: 1) the dosage or frequency of administration is improper; 2) the owner is not complying with instructions or is not successfully administering the medication; 3) the animal is not absorbing the medication well, or is metabolizing and / or excreting it too rapidly; 4) the medication is outdated; or 5) the diagnosis is incorrect. (merckvetmanual.com)