The use of thyroid hormone or antithyroid drug treatment can, over time, produce the opposite effect, especially if the dose of medication given is too high. This means that if you are taking antithyroid medication for hyperthyroidism, you could become hypothyroid; if you are taking thyroid hormone medication for hypothyroidism, you could become hyperthyroid. Pay close attention to how you feel and be aware of the symptoms for each type of thyroid disorder.