Radioactive Iodine: What It Is, How It Works, and What You Need to Know

When your thyroid goes off track—whether it’s overactive, enlarged, or cancerous—radioactive iodine, a targeted form of radiation used to destroy thyroid tissue without surgery. Also known as radioiodine therapy, it’s one of the most common and effective treatments for thyroid disorders in adults. Unlike surgery, it doesn’t require cuts or anesthesia. Instead, you swallow a capsule or liquid that travels straight to your thyroid, where the radiation does its job and then fades away.

Radioactive iodine works because your thyroid naturally pulls iodine from your blood to make hormones. When you take radioactive iodine, your thyroid can’t tell the difference—it absorbs it just like regular iodine. Once inside, the radiation destroys overactive cells or leftover thyroid tissue after surgery. This is why it’s used for hyperthyroidism, a condition where the thyroid makes too much hormone, and for thyroid cancer, especially after removal of the gland to kill any remaining cancer cells. It’s not used for every thyroid problem, but when it’s right, it’s precise, safe, and often a one-time fix.

What you need to know before treatment? You’ll likely be put on a low-iodine diet for a week or two to make your thyroid extra hungry for iodine—so it grabs the radioactive kind more efficiently. You’ll also stop taking thyroid meds temporarily to boost the effect. After treatment, you’ll need to avoid close contact with others for a few days because your body will give off small amounts of radiation through sweat, saliva, and urine. Most people go home the same day, but you’ll get clear instructions on how to protect kids, pets, and partners.

Side effects are usually mild: dry mouth, taste changes, or a sore throat. Some people feel tired for a while. The biggest long-term effect? You’ll probably need to take thyroid hormone pills for the rest of your life because your thyroid won’t be able to make enough on its own. That’s not a failure—it’s just part of the plan. The goal isn’t to keep your thyroid alive; it’s to stop the disease.

Radioactive iodine isn’t for everyone. Pregnant women can’t have it. People with severe eye problems from Graves’ disease might need other options. And if you’re trying to get pregnant, you’ll need to wait several months after treatment. But for millions of people with thyroid issues, it’s the simplest, most direct path to feeling normal again.

Below, you’ll find real-world guides on how this treatment fits into broader health decisions—from managing side effects to understanding how it compares to surgery or medication. Whether you’re preparing for treatment, recovering from it, or just trying to understand why your doctor recommended it, these posts give you the facts without the fluff.