Radioactive iodine treatment is a go-to for certain forms of hyperthyroidism. If your doctor recommends this treatment, you may want to know what to expect and the side effects.
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Hyperthyroidism is when your thyroid gland produces too much thyroid hormone. This hormone regulates many of your body's systems, so having too much of it can speed your system up, resulting in faster metabolism and various symptoms.
Symptoms are highly variable as thyroid hormone levels affect people differently. But common symptoms include:
Rapid or irregular heartbeat
Tremor, especially in the hands
Reduced tolerance of heat
More frequent bowel movements
Enlargement of the thyroid gland called a goiter
Hyperthyroidism is diagnosed by simple blood tests that first look at the amount of thyroid-stimulating hormone (TSH) in your system. TSH is produced by the pituitary gland to regulate the thyroid. If your thyroid is overactive, your pituitary gland will try to dial things back by making less TSH.
Radioactive iodine treatment is recommended for chronic hyperthyroidism. This is most commonly caused by Graves' disease but can also be caused by overactive nodules or lumps on your thyroid. Temporary hyperthyroidism, on the other hand, is typically treated with medication.
Risk factors for Graves' disease include having a family history and being female. It can cause many complications, including Graves' ophthalmology (an eye disease that can cause vision loss), osteoporosis, heart failure, and/or infertility.
Radioactive iodine is also called I-131, and it is essentially an isotope of iodine that is mildly radioactive. The amount depends on the purpose, with the dose for radioactive iodine therapy being fairly high.
Your thyroid gland is extremely thirsty for iodine and will absorb almost all that enters your body; this means that the iodine will travel straight to your thyroid and collect there. The radiation will then damage cells in your thyroid, reducing the efficiency of your thyroid gland and the amount of hormone it produces. This has fewer side effects than long-term use of antithyroid medication.
After treatment, it is relatively common to be left with an underactive thyroid, meaning you may need lifelong therapy with levothyroxine. However, this has fewer side effects than antithyroid medication, and you can go on to lead a normal life.
In most cases, the treatment is permanent. If you become hypothyroid, your hyperthyroidism is highly unlikely to come back. If you experience hyperthyroid symptoms while on levothyroxine, then this most likely means that your dosage is too high and needs to be reduced.
However, this has only been known to happen in extremely rare¹ cases. It's also possible for your hyperthyroidism to return if the radiation dosage was insufficient, requiring another round of treatment.
Another situation where it can come back is if you have Marine-Lenhart Syndrome². This is a rare condition in which you have Graves' disease and overactive nodules in your thyroid. The nodules may grow after treatment. However, this syndrome is estimated to occur in only 0.8 to 2.7% of patients with Graves' disease.
For the vast majority of patients, your hyperthyroidism will not come back.
RAI treatment is associated with some short-term side effects, which typically go away in a relatively short period. There may also be other issues.
Side effects include:
Nausea and vomiting
Swelling and tenderness of the salivary glands; this side effect can be mitigated by chewing gum or sucking on hard candy to get your salivary glands working
Swelling and tenderness of the neck
Changes in your sense of taste, which are typically temporary
Dry eyes: you should not wear contact lenses for some time after treatment
Longer-term side effects or risks include:
Low sperm count, although typically only after multiple treatments, which are rare for Graves' disease.
Irregular menstruation, which can last as long as a year; if you can get pregnant, you should use birth control for at least six months.
A very slight increased risk of developing leukemia, stomach cancer, or salivary gland cancer
Yes, but only for a few days. Some clinics will keep you in the hospital for the first few days. If you are allowed to return home, you will be required to stay three feet from other people for eight hours. After that, you should:
For two days:
Not share eating utensils, cups, etc. with others and wash everything you use promptly
Not share towels or washcloths
Flush the toilet twice after use
Rinse the sink and tub after use
Wash your towels, bed linens, underwear, and any clothing you have sweated on
For one week:
Avoid young children and infants
Avoid kissing and physical contact
Stay three feet away from pregnant people and children under 18
Avoid activities where you will be close to others, such as movie theaters and public transportation
Again, some clinics will keep you in the hospital in isolation to reduce the risk. You should stop six weeks before treatment and should not resume if you are breastfeeding, although it will be safe for you to breastfeed in subsequent pregnancies. If you need to travel within three months, get a doctor's note as you may set off radiation scanners.
Some people should not receive radioactive iodine treatment. These include:
People who are pregnant or could be pregnant; your doctor will insist on a pregnancy test, and you must wait at least six months after treatment before trying to become pregnant.
People who have moderate to severe Graves' ophthalmology³; whereas those with mild Graves' ophthalmology should receive oral prednisone from a few days before the therapy to one to three months afterward
People who have chronic conditions that cause vomiting or diarrhea
The biggest reason not to receive radioactive iodine treatment is pregnancy, as it can cause permanent damage to the child's thyroid and developmental problems. Men who will receive multiple treatments are advised to freeze sperm in case of fertility damage.
There are two other main treatments for hyperthyroidism:
These medications stop the thyroid from producing hormones. There are two approved in the U.S., namely propylthiouracil (PTU) and methimazole. PTU is typically given to pregnant women as it has a much lower risk of causing congenital disabilities.
However, it has to be taken three times a day and can have more long-term side effects. Methimazole is generally better tolerated but is not safe during pregnancy.
Surgery to remove part or all of the thyroid gland. Generally, surgery is recommended only in patients for whom radioactive iodine therapy is not recommended. It is relatively invasive and causes a fair bit of scarring.
Radioactive iodine treatment is a go-to treatment for long-term hyperthyroidism, most often caused by Graves' disease. It is typically safe in the long term, although short-term side effects can be unpleasant. However, it is not recommended during pregnancy.
Your doctor will likely recommend radioactive iodine treatment if you have Graves' disease. It often leaves you with an underactive thyroid, which you can manage with inexpensive medication.
Although the treatment sounds alarming, it is often the best route to a normal life.
Radioactive iodine therapy (2022)
Hyperthyroidism (overactive) | American Thyroid Association
Hyperthyroidism (overactive thyroid) | NIH: National Institute of Diabetes and Digestive and Kidney Diseases
Radioactive iodine (radioiodine) therapy for thyroid cancer | American Cancer Society
Fact sheet: Guidelines for patients receiving radioiodine I-131 treatment | Society of Nuclear Medicine & Molecular Imaging
Antithyroid medications for hyperthyroidism | Endocrine Web