A complication of hyperthyroidism is heart problems, which often occur in older people. Hyperthyroidism can cause a fast or irregular heartbeat, as well as congestive heart failure.
Another complication is weak or brittle bones and osteoporosis. The thyroid gland controls how much calcium is used by the body. An overactive thyroid gland diminishes how much calcium gets incorporated in your bones.
Graves' disease can lead to sore and swollen skin, as well as to eye problems, like bulging or dry eyes.
Another complication is thyrotoxic crisis. This is a condition in which the symptoms of hyperthyroidism intensify, causing a rapid heartbeat, fever, and delirium.