Check your thyroid function before taking Synthroid. Those who have hyperthyroidism should not take it. If you decide to discontinue use of the drug (you can buy Synthroid without prescription) because of its side effects try to do it as gradually as possible. Synthroid is also used to treat or prevent enlarged thyroid gland – goiter, to treat low thyroid hormone – hypothyroidism. If you want to buy Synthroid online and have no prescription.