Radiation for hyperthyroidism: what to know

It is taken by mouth and is absorbed mainly by thyroid tissue. A clinician may suggest it when medicines are not suitable, have not controlled the overactive thyroid well enough, or are not preferred.

The iodine gives off radiation within the thyroid, gradually reducing the gland's hormone production. Symptoms of hyperthyroidism, such as palpitations, heat intolerance, excessive sweating, diarrhoea, feeling anxious or difficulty sleeping, may ease as thyroid hormone levels settle.

The change is gradual rather than immediate. Some people later develop an underactive thyroid and need thyroid hormone replacement; blood tests show whether this is needed and help guide the dose.

Tell the treatment team about every medicine and supplement you take, especially thyroid medicines or products containing iodine. They will tell you whether any need to be paused and give personalised instructions about food, travel, close contact and hygiene after treatment.

Keep all follow-up appointments even if you feel well. Contact the clinician managing your thyroid if symptoms continue, return, or change, because treatment and blood-test timing may need adjustment.

Seek urgent medical care for chest pain, severe shortness of breath, fainting, confusion, or a very fast or irregular heartbeat. These symptoms need prompt assessment whether or not you have had radioactive iodine.

Contact your thyroid clinician promptly if you develop worsening tremor, persistent vomiting, marked weakness, fever with severe restlessness, or troublesome swelling or pain in the neck.

Ask whether radioactive iodine is appropriate for your cause of hyperthyroidism, how your current medicines will be managed, when blood tests are planned, and what precautions apply at home or work. If pregnancy is possible, or you are breastfeeding, raise this before treatment because the plan needs specialist guidance.