How is hashimoto's thyroiditis different from grave's disease?

Thyroid Levels: Hashimoto's and and graves' disease are both caused by autoimmunity (where antibodies attack one's own proteins). Hashimoto's more often results in low thyroid hormone levels. Where graves' disease almost always results in high thyroid hormone levels.

Different diseases: Both are autoimmune thyroid diseases, but hashimoto's antibodies are directed against the thyroid gland, causing its destruction. Grave's antibodies mimic tsh, which stimulates the thyroid gland to make lots of thyroid hormone, thus an overactive gland. Patients with grave's disease often also have hashimoto's antibodies. In some cases, the destruction may just burn out the gland over time.