The People's Perspective on Medicine

Radioactive Iodine for Hyperthyroidism Increases Cancer Risk

Would you believe that I-131 has been administered for over 70 years? Only now do we learn that radioactive iodine for hyperthyroidism might cause cancer.
Doctor palpates patient’s neck to check thyroid gland

A new study in JAMA Internal Medicine (July 1, 2019) has linked exposure to radioactive iodine for hyperthyroidism to a 6 percent increased risk of death for all solid cancers and a 12 percent increased risk of death for breast cancer.  Before you panic, however, please recognize that the absolute risk is relatively small. The authors note: “For every 1000 patients currently treated at age 50 years, we estimated an excess of 12 radiation-associated solid cancer deaths, including 3 breast cancer deaths.” Most of these deaths occurred more than 20 years after the original treatment.

What is Hyperthyroidism?

Mention thyroid problems and most people assume you are talking about HYPOthyroidism or underactive thyroid function. That’s because it is extremely common. But a substantial number of people have the opposite condition, ie, HYPERthyroidism. It is also called Graves’ disease.

In this autoimmune condition, the thyroid gland goes into overdrive. Symptoms include hand tremor, weight loss, insomnia, anxiety, restlessness, sensitivity to heat, frequent trips to the bathroom, rapid pulse or irregular heart rhythms.

Why Would Anyone Take Radioactive Iodine for Hyperthyroidism?

To “cure” hyperthyroidism, doctors have been prescribing radioactive iodine (I-131) since the 1940s. Abbreviated RAI, this treatment for Graves’ disease is the most common hyperthyroid treatment in the United States. The radioactive iodine is taken up by the thyroid gland and basically zaps the tissue, leaving the gland nonfunctional. Find out more about this process and unexpected consequences at this link.

Health professionals generally prefer this approach because radioactive iodine for hyperthyroidism is permanent. They often refer to RAI as “a safe and effective definitive treatment for Graves’ disease” (BMC Endocrine Disorders, Dec. 12, 2018). 

The alternatives for treating Graves’ disease are surgery or thyroid-suppressing drugs. Medications like methimazole or propylthiouracil are not considered as reliable as RAI. Thyroid surgery (total thyroidectomy) is usually reserved for therapeutic failures. It is generally the last choice for treating hyperthyroidism (Journal of Community Hospital Internal Medicine Perspectives, online, Sept 7, 2016). 

Problems with Radioactive Iodine for Hyperthyroidism:

When I learned about I-131 in graduate school at the Univeristy of Michigan, the professor was somewhat cautious. He implied that this radioactive isotope of iodine might have long-term consequences that had not yet been fully discovered.

The latest research seems to have proved him right. The authors tracked nearly 19,000 patients who received radioactive iodine for hyperthyroidism. In some cases this was over nearly seven decades. Without doubt, this is the largest and most comprehensive study of RAI ever undertaken.

We suspect that most health professionals assume that radioactive iodine goes straight to the thyroid gland without impacting any other organs. Although the thyroid gets by far the biggest dose of radiation, other organs are exposed. They include the esophagus, stomach, lungs, female breast, pancreas, kidney, uterus, brain, bladder, ovary, prostate, colon or rectum.

The researchers point out that higher radioactive doses are “now currently recommended for the treatment of patients with Graves disease…” The authors project that:

“At these dose levels, we would expect between 19 and 32 excess solid cancer deaths per 1000 patients treated at age 40 years and between 18 and 31 excess solid cancer deaths per 1000 patients treated at age 50 years.”

What to Make of the New Research?

Radioactive iodine for hyperthyroidism has been prescribed for at least 70 years. Only now do we learn that there could be an increased risk of cancer associated with RAI. Please keep in mind that this research in JAMA Internal Medicine (July 1, 2019) is reporting on cancer deaths, not total cancer cases. We suspect that the number of people diagnosed with cancer due to I-131 exposure is substantially higher.

That said, the authors emphasize that this is a relatively small risk. They offer these thoughts on the significance of their research.


“This study’s findings suggest a modest positive association between greater organ-absorbed doses of radioactive iodine and risk of solid cancer death; additional studies are needed to fully weigh the risks and advantages of radioactive iodine and other treatment options for patients with hyperthyroidism.”

So, 70 years after radioactive iodine for hyperthyroidism was introduced into “modern medicine,” we are told that “additional studies are needed.” Seems to us that the horses have been out of the barn for a very long time.

If you are interested in HYPO- and HYPERthyroidism, you may wish to listen to our interview with Dr. David Cooper, Director of the Thyroid Clinic at Johns Hopkins University. Here is a link to the streaming audio or the free mp3 podcast.

Hyperthyroidism in Cats!

You may also want to learn about the epidemic of hyperthyroidism in cats. Don’t let the title about dental floss fool you. It isn’t just cats, and it’s not just dental floss. This article discusses endocrine-disrupting chemicals that might be contributing to hyperthyroidism.

Does Your Dental Floss Contain PFAS Chemicals That Disrupt Hormones?

Share your own experience with radioactive iodine for hyperthyroidism in the comment section.

Rate this article
4.9- 17 ratings
About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
Thyroid Hormones

What symptoms signal thyroid trouble? The 25-page downloadable Guide to Thyroid Hormones has critical info on testing, treatment, and side effects. © 2015

Thyroid Hormones
  • Kitahara, C. M., et al, "Association of Radioactive Iodine Treatment With Cancer Mortality in Patients With Hyperthyroidism," JAMA Internal Medicine, July 1, 2019,doi:10.1001/jamainternmed.2019.0981
Join over 150,000 Subscribers at The People's Pharmacy

We're empowering you to make wise decisions about your own health, by providing you with essential health information about both medical and alternative treatment options.

Showing 3 comments
Add your comment

I was treated with RAI for hyperthyroidism many years ago, around 1980. For about 12 years my thyroid function was in the normal range until I was diagnosed with hypothyroidism and was put on levothyroxin. In 1993 ‘nasty’ ovarian cyst was discovered, which would have eventually become malignant had it not been discovered so early. A total hysterectomy followed and five years of follow-up at a cancer clinic. In 2009 I developed thyroid cancer (papillary) and had a thyroidectomy (entire thyroid removed). Three months later I had another radioactive treatment in the hospital, which kept me in isolation for three, entire, long, painful days. The pains in my hands were the effects of having to go off synthroid for a prior to the treatment. Approximately three months later, and again a year after that, I had complete body scans to make sure there was no thyroid tissue “floating” in my body. All clear.

In 2013, on a yearly, routine mammogram — guess what! — breast cancer. Luckily, the tumor was very small and because of my age (70), I was lucky enough to need only a lumpectomy and tissue samples taken from the lymph nodes. The lymph node biopsies and margins on the tumor were clear, no chemo or radiation needed, and I was put on a five-year plan taking letrozole daily.

So, was the RAI treatment in 1980 the cause of my having those cancers? I don’t really expect an answer, but your article has me wondering just that. I hope this monologue isn’t too lengthy to post on your web site — I just want make others aware that RAI treatment should be looked at very carefully if it is recommended for you.

RAI was recommended to me (as a diagnostic test) in the early 1970s because I had an enlarged thyroid. I said no. In the years before menopause, I continued to have normal thyroid blood tests, but an enlarged thyroid. After menopause, my thyroid has gradually become normal-sized.

I was told I had radioactive iodine administered to my thyroid as a baby. Drs in the early 1940s thought the thyroid sometimes continued to grow after birth & would choke a baby.
In 1981 I was diagnosed with hypothyroid. I suspect it was due to the treatment I received as a baby.
I take Armour thyroid and am doing very well.

* Be nice, and don't over share. View comment policy^