Are You Getting Radioactive Iodine Treatment For Your Overactive Thyroid? Here's What You Need To Know

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.

Have you considered clinical trials for Hyperthyroidism?

We make it easy for you to participate in a clinical trial for Hyperthyroidism, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

What is hyperthyroidism?

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:

  • Unexplained weight loss

  • Rapid or irregular heartbeat

  • Insomnia

  • Fatigue

  • Nervousness

  • Irritability

  • Weakness

  • 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.

What is radioactive iodine?

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.

How is radioactive iodine used to treat hyperthyroidism?

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.

Does the treatment prevent a recurrence?

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.

What are the side effects of RAI treatment?

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

  • Dry mouth

  • 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.

  • very slight increased risk of developing leukemia, stomach cancer, or salivary gland cancer

Will you be radioactive after treatment?

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

  • Sleep alone

  • 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.

Who should not receive radioactive iodine treatment?

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.

Other treatments for hyperthyroidism

There are two other main treatments for hyperthyroidism:

Anti-thyroid medication

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.

The lowdown

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.

Have you considered clinical trials for Hyperthyroidism?

We make it easy for you to participate in a clinical trial for Hyperthyroidism, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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