Sodium Iodide I 131 (Oral)

Sodium iodide I 131 is an oral medication that targets the thyroid gland. It contains iodine, a radioactive agent and is used in smaller doses when treating hyperthyroidism (otherwise known as an overactive thyroid gland) or in larger doses to treat specific types of thyroid cancer.


Otherwise known by its brand name, Iodotope, sodium iodide I 131 is a radioisotopic medicine that is used to treat an overactive thyroid (hypothyroidism), specific types of cancer and, in some cases, diagnose thyroid conditions. When in the body, this medicine becomes trapped in the thyroid gland and can be used in either small or large dose to treat different conditions.

Iodide is a radioactive agent that, when used in smaller doses, irradiates and causes damage to the thyroid gland. This actively reduces its activity and the production of thyroid hormone, making an effective treatment for hypothyroidism. When used in larger doses, sodium iodide | 131 is effective at destroying remaining cancerous thyroid tissue after thyroid cancer surgery, or it can be used to kill thyroid cancer that has spread.

In some cases, a doctor will prescribe minute doses that can help diagnose issues within the thyroid gland. By using such small doses, your doctor will be able to use the measure of radioactivity that is visible in the gland to determine whether it is working properly, or whether there are any thyroid cancer-causing tumors within the thyroid.

Even though sodium iodide I 131 does fall within the category of anti-thyroid medication, it is also classed as a Radioisotopic medicine due to its radioactive properties. Once absorbed into the body, it becomes focused on the thyroid gland and the kidneys will actively dispose of any excess medication by eliminating it from the body through urine. Over a period of several weeks, any sodium iodide | 131 that remains in the body will lose the majority of its radioactivity with the half-life of its radioactivity being eight days. It is taken orally, in the form of capsules and must only ever be administered or supervised by a healthcare professional who has been trained in nuclear medicine or radiation oncology.

Conditions Treated

Type of Medicine

  • Anti-thyroid
  • Radioisotopic

Side Effects

When taking sodium Iodide I 131, there is a possibility of experiencing unwanted side effects. For many patients, there may be no side effects, or they might be minor ones that disappear once the body has adjusted to the medication. Following treatment for hypothyroidism, you may experience the temporary thinning of hair, changes in menstrual periods, clumsiness, the feeling of being cold, drowsiness, unusual tiredness or weakness, and lethargy. You may also experience headaches, drowsiness, muscle aches and weight gain. These are all symptoms of an underactive thyroid and should be alerted to your doctor immediately.

Commonly experienced reactions to this medication after being treated for hypothyroidism also include neck tenderness or swelling and a sore throat. In most cases, these are harmless reactions that will go away in time and do not need medical attention. However, if you find that they remain persistent or are causing you concern, make sure to discuss it with your doctor.

There is also a chance that you may experience rare side effects after the treatment of an overactive thyroid. If you notice any excessive sweating, a fast and abnormal heartbeat or pulse, fever and unusual irritability, these may be signs of a more serious reaction to the medication. If you experience any of these reactions, make sure to contact a medical professional when possible.

In very rare and severe cases, patients who have been treated for an overactive thyroid may have reactions to this medication that require immediate medical attention. Sudden chest pain, hives, itching and a rash, a pounding and irregular heartbeat, nervousness, heat sensitivity and tenderness of the salivary glands can all indicate more serious reactions and should receive medical attention immediately.

Following treatment for thyroid cancer, many patients experience a temporary loss of taste, nausea and vomiting and the tenderness of the salivary glands. Usually, these are all be temporary reactions that will disappear once the medication has adjusted or left the system. However, it is always important to discuss them with your doctor if they concern you.

If you are receiving this medication to treat thyroid cancer, it is important that you keep track of any side effects that you may experience. If you happen to notice blood in the urine or stools, a cough or hoarseness, fever, chills or lower flank pain, make sure you see a doctor as soon as possible. Any pain or difficulty swallowing, difficult or painful urination, pinpoint red spots on the skin or unusual bleeding or bruising must also be reported to a healthcare professional.

In addition to this, any abdominal cramps, bleeding gums, bone pain, diarrhea or vomiting, nausea and a loss of appetite can be indicators of rare and serious conditions caused by the medication. If you also experience a feeling of discomfort, sore throat or lethargy, make sure to alert your doctor.


Your dose of Sodium Iodide I 131 will be dependent on a number of factors including your condition, treatment plan, weight and any other illnesses or medical conditions that you may suffer from. Prior to the treatment, you should be measured by an adequate radioactivity system that will help your doctor determine your dose.

When using sodium Iodide I 131 in thyroid uptake diagnostic procedures, the average adult will be given a capsule of five to 15 microcuries of the medication for diagnosing thyroid uptake. To determine the localization of extrathyroidal metastases, this dose will be 1000 microcuries.

The capsule dose for therapeutic purposes (the treatment of disease) can range from 0.75 to 100 microcuries, whilst capsule doses for thyroid cancer treatment range from 30 to 100 microcuries for ablation of normal thyroid tissue. Subsequent metastases ablation (the removal of remaining cancerous tissue) has a capsule dose of 100 to 200 microcuries.

A much smaller dose is given to patients taking for the treatment of hypothyroidism. The standard dose for this treatment tends to range from four to 10 microcuries, however toxic nodular goiters or other more serious thyroid conditions may also require larger doses.


This medication can have interactions with numerous other medicines, some of which may cause damaging reactions or altercations to your treatment. There are 457 medicines that can cause moderate interactions with sodium Iodide I 131 making it incredibly important for you to be as transparent as possible with your doctor. If you happen to be taking any forms of amiodarone, it is vital that you let your doctor know, as this drug can cause severe implications when taken with sodium Iodide I 131.

The below medicines can all affect the therapeutic efficacy of your treatment, making it less effective. Make sure to tell your doctor if you are taking any of the following:

  • Adderall (amphetamine / dextroamphetamine)
  • Carbimazole
  • Levothyroxine
  • Liothyronine
  • Liotrix
  • Methimazole
  • Methylthiouracil
  • Potassium Iodide
  • Propylthiouracil
  • Thyroid, porcine

As this medication has the potential to interact with such a wide range of medications, it is essential that your doctor is familiar with any prescription or over the counter medications that you take in advance to your treatment. For peace of mind, also make sure to include any herbal remedies, supplements or vitamins when discussing this with your doctor.


The radioactive properties of this medication can pose some risks to your health, however, your doctor will only ever prescribe sodium Iodide I 131 if the benefits far outweigh any dangers. Because it is taken orally, it is likely that your doctor will instruct you with some guidelines that should be followed the 48 to 96 hours after treatment. This will reduce any chances of contaminating other people.

If you are receiving this medication, your doctor may instruct you to follow these instructions for 48 to 96 hours after taking sodium Iodide I 131. This will help to reduce the chance of spreading radioactive particles to other people. These guidelines include the discontinuation of having sex, kissing, sharing food or handling and using anyone else's eating or drinking utensils and toothbrush. You should also not sit next to others, in particular, pregnant women who are most at risk, and not hold children for extended periods of time. Alongside this, you should sleep alone, wash the shower, bathtub or sink thoroughly after use (especially after brushing teeth), wash your hands regularly, use separate towels and washcloths and launder your clothes, bed linens and wash your eating utensils separately to others. Because sodium iodide I 131 is expelled through urine, it is also important that you flush the toilet two times after urination, as this will prevent contamination.

It is important to discuss the effects of this medication and pregnancy and fertility with your doctor prior to your treatment. To use sodium iodide I 131 can cause serious harm to an unborn baby, and if you are pregnant, an alternative treatment may be appropriate. Your doctor may give you a pregnancy test in advance to treatment with this medication, to ensure that you are not pregnant and at risk. Following your treatment, it is important that you combine two forms of birth control for a minimum of six months from its end date. This is to prevent pregnancy and harm an unborn baby. If you suspect that you have become pregnant during your treatment or shortly after, you must inform your doctor as soon as possible.

In addition to this, sodium iodide I 131 can cause temporary infertility in men and women. This is usually temporary and should not pose any risk to future fertility, however, if you are concerned at all, it is important that you discuss it with your doctor.


This medication should only ever be handled by a healthcare professional who is licensed to use radiopharmaceuticals and radioisotopes. You should never have direct access to it, and it will only ever be administered by a doctor or trained professional. It should be kept at a controlled temperature of 20-25°C and disposed of immediately if it reaches its expiry date.


Sodium iodide I 131 is an effective treatment for thyroid-specific conditions such as hypothyroidism and certain types of cancer. When used in small doses, it is also an efficient way of diagnosing problems within this area. Featuring a radioactive agent, this medicine is able to cause damage to the thyroid and successfully slow down the thyroid gland production of hypothyroidism causing hormones. When used in larger doses, it is an effective way to destroy cancerous tissue that may remain after primary treatment.

The administration of this medication is quick and effective, taken orally in the form of capsules and under the direct supervision of a doctor. For patients receiving this treatment for thyroid cancer, in particular, this is a much less daunting prospect than intravenous administration.

Although the administration of the medication is relatively quick and easy, it has prolonged effects that can potentially cause harm others, and this requires a level of responsibility and commitment that some may find daunting. Following treatment from this medication, it is important to ensure that any risks to others are minimized by following instructions that include sleeping alone, not sharing food or food utensils and the discontinuation of kissing and sex. These only need following in the 48 -to 96 hours after treatment and can be easily managed and advised by the help of your doctor.

Sodium iodide I 131 can also cause temporary infertility and is harmful to unborn babies during and after treatment, so patients must be diligent with contraception for at least 6 months following treatment. Alongside this, you must also keep an eye on any side effects and report them to your doctor.

With successful treatment, this medication can have a hugely positive impact on your life, helping your body to regulate thyroid hormone and treat hypothyroidism, as well as act as a final step in a cancer treatment plan. Your doctor will keep a close eye on you during your treatment process, and will likely run blood and urine test in the following weeks to track and help manage any unwanted effects. It is also common for doctors to run blood tests every two to three months in the first year to check the level of thyroid hormone. This can help alleviate any anxieties that this medication may cause, and assure you with a trained professional offering advice and help when needed.


Last Reviewed:
January 30, 2018
Last Updated:
April 05, 2018