Radioactive Iodine (RAI) Therapy: What you need to know

Radioactive Iodine (RAI) Therapy: What you need to know

Dr. Natalie Bessom
Medically reviewed by

Natalie Bessom, D.O. Board-certified family medicine doctor with specialty training in nutrition, USA

The name “radioactive iodine” may seem a little scary but it’s actually a common treatment approach for hyperthyroidism (overactive thyroid gland) and thyroid cancer.

Radioactive iodine therapy (RAI), also known as I-131 therapy or radioiodine therapy, is a safe, normally well-tolerated, and common treatment that targets the thyroid cells. The thyroid gland is the only organ in the body that absorbs iodine. This makes the administration of radioactive iodine safe as thyroid cells can be easily targeted with high doses of radiation without affecting other parts of the body.

RAI typically comes as a pill, but is occasionally given in liquid form. While thyroid patients may be familiar with two radioactive forms of iodine (I-123 and I-131), only I-131 is used for treatment of hyperthyroidism and thyroid cancer as it is capable of destroying thyroid cells, while I-123 is mainly used for thyroid imaging purposes as it is harmless to thyroid cells.

Now that we know what radioactive iodine therapy is, the rest of this article will focus on the following:

  • How exactly does RAI therapy work?
    • Possible side effects of radioactive iodine therapy
    • Precautions to be taken for radioactive iodine therapy
  • What are the unique concerns for women and men who undergo radioactive iodine treatment?

How exactly does RAI therapy work?

Radioactive iodine therapy is most commonly used to treat thyroid cancer (typically papillary and follicular thyroid cancers). Large doses of I-131 are used, after surgical removal of the thyroid gland (thyroidectomy), to destroy any remaining thyroid tissue or cancer cells that may be present in the body. This helps to prevent the cancer from coming back or spreading to other parts of the body. Radioactive iodine therapy cannot be used to treat anaplastic (undifferentiated) and medullary thyroid carcinomas because these types of cancer do not absorb iodine.

The therapy is also used to treat hyperthyroidism, a condition characterized by an overactive thyroid gland that produces too much thyroid hormone. Hyperthyroidism can cause a range of symptoms, including weight loss, nervousness, irritability, sweating, sleep problems, and a rapid heart rate. Radioactive iodine therapy can help regulate the production of thyroid hormone and alleviate these symptoms. The I-131 dosage for treating hyperthyroidism is significantly less than treating thyroid cancer.


Before treatment…

Patients are required to fast for a few hours to ensure proper absorption of the radioactive iodine.


Following oral administration of radioactive iodine and its subsequent rapid absorption by the thyroid cells, these cells get destroyed from the radiation that is emitted. This results in a reduction in size and activity of the thyroid gland.


After treatment…

Patients may experience side effects such as:

  • temporary swelling or tenderness in the neck
  • dry mouth
  • changes in taste or smell
  • nausea  
  • vomiting
  •  diarrhea

The side effects of radioactive iodine therapy are typically mild and transient. Patients are usually monitored for a few hours afterwards to ensure proper uptake of the radiation. Follow-up appointments are scheduled to monitor thyroid function and ensure proper healing. The treatment will most likely cause the thyroid gland to become underactive (hypothyroidism). This can be treated with replacement thyroid hormone replacement therapy.

It is worth noting that RAI therapy is a non-invasive procedure and typically lasts only a few minutes, with no need for anesthesia or surgery. Patients are expected to be able to get back to their usual activities within a few days after the therapy.


However, in order to reduce radiation exposure, there are some precautions that patients need to take for a period of time after the treatment, such as:

  • maintaining a safe distance from others and avoiding public places
  •  avoiding close contact particularly with pregnant women and young children
  •  avoiding the sharing of utensils or personal items.

Your healthcare provider will provide specific instructions afterwards on how to prevent radioactive exposure to others. The length of time you need to follow these instructions and safety measures will depend on the strength of your RAI dose.

What are the unique concerns for women and men who undergo radioactive iodine (RAI) treatment?

Besides the risk of developing a second cancer due to exposure to radiation, there are some special concerns for men and for women who undergo RAI therapy.

The radiation released by the treatment can damage or negatively affect other organs, such as the ovaries or testes. According to the American Cancer Society, men who receive large total doses of radiation because of repeat RAI treatment may have lower sperm counts or, rarely, become infertile.

Some women may have irregular periods (spotting/inconsistency) for up to a year after treatment. Women who undergo RAI treatment should not be pregnant or nursing during treatment. The point of this is to protect the baby from receiving radioactive milk. The American Thyroid Association recommends that breastfeeding must be stopped at least 6 weeks before administration of I-131 treatment and should not be restarted after administration of RAI, but can be safely done for future pregnancies.

Furthermore, any attempts to conceive should be put off for at least 6 – 12 months after RAI therapy. This ensures that the ovaries have adequate time free of radiation exposure and for thyroid hormone levels to return to normal and become stable before pregnancy. 

Key Takeaways

  • Radioactive Iodine Therapy (RAI) common way to treat an overactive thyroid (hyperthyroidism) and thyroid cancer
  • Radioactive Iodine Therapy (RAI) is given as a pill or liquid form to treat hyperthyroidism and thyroid cancer
  • RAI treats hyperthyroidism and thyroid cancer by destroying thyroid cells with doses of I-131 
  • The end result of RAI treatment is typically hypothyroidism (underactive thyroid), which is treated by thyroid hormone replacement
  • Side effects of RAI include dry mouth, changes in taste or smell, nausea, and vomiting
  • After receiving RAI, you may be required to stay in a specially isolated room in the hospital to prevent others from being exposed to radiation
  • Men who receive large total doses of radiation because of many treatments with RAI may have lower sperm counts or, rarely, become infertile
  • Women who are pregnant or breastfeeding should not undergo RAI to prevent the baby from being exposed to radiation and drinking radioactive milk

Undergoing treatment for thyroid cancer can be difficult to understand and manage. ThyForLife was built by a thyroid cancer survivor after her own battle. 

The ThyForLife app can help you easily manage the different aspects of your thyroid health journey from bloodwork, medication, supplements, symptoms and more – so you can get back to focusing on what matters.


Radioactive iodine therapy is a treatment method used for thyroid conditions such as hyperthyroidism and thyroid cancer. It involves ingesting a dose of radioactive iodine, which is absorbed by the thyroid gland. The radiation emitted by the iodine destroys thyroid tissue, thereby reducing thyroid function or targeting cancerous cells.

Radioactive iodine therapy can help regulate thyroid function in cases of hyperthyroidism by reducing the production of thyroid hormones. For individuals with thyroid cancer, it can target and destroy cancerous thyroid cells, potentially preventing the spread or recurrence of the disease.

While radioactive iodine therapy is generally safe and well-tolerated, there are potential side effects and risks to consider. These can include temporary symptoms such as neck pain, nausea, dry mouth, and changes in taste or smell. In some cases, there may be a risk of radiation exposure to other tissues or organs, although precautions are taken to minimize this risk.

Radioactive iodine therapy is typically recommended for specific cases of hyperthyroidism and thyroid cancer. The decision to undergo this treatment depends on various factors, including the type and severity of the thyroid condition, individual health considerations, and treatment goals. It’s essential to consult with a healthcare provider to determine if radioactive iodine therapy is appropriate for your specific situation.


At ThyForLife, we do our utmost to provide accurate information. For detailed medical information regarding diagnosis, treatment, and general practices please consult your healthcare professional. Always listen to the advice of your healthcare provider.
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