Initially overactivity of the thyroid is treated by a course of tablets but when this fails to control the thyroid, Radioactive iodine treatment is a possible next option.
Radioactive iodine is taken by mouth as a capsule typically with a glass of water. The radioactivity in the capsule only lasts for a few days and for 90% of patients, one dose is sufficient to control the over activity. About 10% of patients may need a second dose but a third dose is rarely needed. A second dose would be considered if a patient still needed to take carbimazole or propylthiouracil tablets to control their overactive gland six months after they had received their first dose of radioactive iodine.
The thyroid is very efficient at extracting iodine from the blood so the vast majority of the radioactive iodine is taken up by the thyroid gland. Very little of it goes elsewhere in the body. The radioactivity is therefore targeted at the thyroid gland.
Radioactive iodine takes at least a month to start to work and may take much longer. Some patients will be advised to re-start their carbimazole or propylthiouracil tablets one week after receiving their radioactive iodine, others do not. Your specialist with provide advice about this.
Thyroid blood tests are monitored every four to six weeks in clinic and your treatment will be adjusted according to the results.
Radioactive iodine treatment is commonly used and generally safe. You will be provided with advisory precautions to ensure that the treatment is as safe as possible for you and your family, friends and colleagues.
Most importantly, you should not be given radioactive iodine if there is any possibility that you might be pregnant. Detailed information will be provided to you before any treatment commences.
Radioactive iodine treatment will nearly always ensure that your thyroid gland becomes underactive at some point. As a rough guide 30% of patients are likely to develop an underactive thyroid gland within a year of treatment, increasing to approximately 70% of patients after ten years. This is the reason for undergoing regular blood tests to pick up emerging thyroid under activity so that treatment with thyroid hormone tablets (Thyroxine) can be started. Under activity of the thyroid gland should not make you put on weight provided it is detected and treated.
Your thyroid blood tests should be done at least once a year following radioactive iodine treatment. This is usually done by your general practitioner.
There is specific advice for those considering pregnancy with women advised to avoid pregnancy for six months and men advised not to father children for four months after treatment. This is purely precautionary as there is no evidence that this treatment has caused damage to any unborn children.
Very occasionally people with thyroid eye disease have felt that their eyes have got worse after radioactive iodine treatment. If there is a link between radioactive iodine and worsening eye problems it is very rare. You may be advised to have a course tablets at the time of the radioactive iodine to reduce inflammation and prevent changes to the eyes.