There are several possible complications that can occur if you have hyperthyroidism. These are outlined below and are most likely to occur if the condition is left untreated.

Graves' opthalmopathy

Graves' disease is a condition which attacks your thyroid gland and causes it to produce too much thyroid hormone. This makes it the most common cause of hyperthyroidism. If you have Graves' disease, you may also experience problems with your eyes, which is known as Graves' opthalmopathy.

If you have Graves' opthalmopathy, you may experience discomfort in your eyes and problems with vision. You may also find that your eyes 'stand out', or appear more prominent.

In mild cases, the symptoms of Graves' opthalmopathy can be relieved using eye drops, and preventing dust particles from getting into your eyes by wearing sunglasses, and eye protectors while you are sleeping. However, more severe forms of the condition requires specialist treatment.

Thyroid storm

Hyperthyroidism that is undiagnosed, or poorly controlled, can cause a rare but serious reaction called a thyroid storm. This can be brought about by an injury, infection, or a trauma, such as a stroke, or childbirth.

The symptoms of a thyroid storm include a very rapid heart rate (over 140 beats a minute), fever over 38.5 C, or 101 F, and severe agitation, or delusion (see 'symptoms' section). A thyroid storm requires emergency medical treatment in hospital.

Pregnancy and hyperthyroidism

Women with hyperthyroidism who become pregnant are more at risk of developing complications during the pregnancy and birth. If you have hyperthyroidism and you are pregnant, you have an increased risk of miscarriage and eclampsia (seizures during pregnancy). You are also more at risk of going into labor prematurely and having a baby with a low birth weight.

If you are pregnant and you have hyperthyroidism, you should be referred for specialist treatment, so that your condition can be managed using medications that will not affect your baby. Your condition will also need to be carefully monitored throughout your pregnancy.