Radiopharmaceuticals (Oral Route)

Radiopharmaceuticals are a class of drugs that, when taken orally, are used to diagnose a wide range of medical conditions and diseases.


Radiopharmaceuticals are a type of radioactive agent. When being used to diagnose a medical condition, a patient will be given only a very small dose. Radiopharmaceuticals are also used to treat certain diseases or cancers. When used for this purpose, the drugs will likely be administered in much larger doses. The diseased or cancerous cells absorb the radiopharmaceutical drug and are then destroyed by it.

When a patient is administered an oral dose of radiopharmaceuticals for diagnosis, the radioactive agent passes through the body and is taken up by or passed through a particular organ, depending on the condition being diagnosed and the way the radiopharmaceutical has been administered. Radioisotopes are also able to bind specifically to a certain organ. The radioactivity can then be detected in that organ, and the nuclear medicine doctor will use special imaging equipment to look at pictures of the organ. These pictures allow the doctor to see the organ, determine how it is functioning, and diagnose the presence or absence of a particular medical condition. The nuclear medicine doctor can see molecular activity, tumors, tissue metabolism, or other indicators of organ health.

The radioisotope present in the radiopharmaceutical releases penetrating gamma rays. The radiation is then detected by a special device called a SPECT/PET camera. The radiation emitted by the radiopharmaceutical generally disappears after one day due to radioactive decay and normal body excretions. The drug will leave your body after the test in the urine or bowel movement.

There are certain other medical conditions that a doctor may diagnose by administering radiopharmaceuticals in other ways, such as injection or placement in the eye or bladder.

There may be special preparations you need to take before you receive your diagnostic test. Some tests may require fasting beforehand, or drinking extra fluids. Your doctor will tell you about anything particular you need to do to prepare for the test. If you have not received any instructions about test preparation, if you do not understand your instructions, or if you are confused about how to fulfill them, ask your doctor ahead of time. Failing to prepare properly could compromise the accuracy of the test results.

Radiopharmaceuticals should only ever be administered under the direct supervision of a doctor who is trained in nuclear medicine.

Conditions Treated

Diagnosis of:

  • Abscess or infection
  • Biliary tract blockage
  • Blood volume studies
  • Blood vessel diseases
  • Bone diseases and bone marrow diseases
  • Brain diseases and brain tumors
  • Cancer or tumors
  • Colorectal diseases
  • Iron metabolism and absorption diseases
  • Heart disease or heart muscle damage
  • Impairments in the flow of cerebrospinal fluid in the brain
  • Kidney, liver, or lung diseases
  • Parathyroid diseases including parathyroid cancer
  • Pernicious anemia or improper absorption of vitamin B12 from intestines
  • Red blood cell diseases
  • Salivary gland diseases
  • Spleen diseases
  • Stomach and intestinal bleeding or other stomach issues
  • Tear duct blockage
  • Thyroid diseases including thyroid cancer
  • Urinary bladder diseases

Type of Medicine

  • Diagnostic

Side Effects

Along with the intended effects, any medicine may cause unintended side effects as well. Side effects from diagnostic doses of radiopharmaceuticals are rare and are usually a result of an allergic reaction. Side effects may occur immediately or within several minutes of taking the radiopharmaceutical. It may be helpful to note the time when you start experiencing a certain side effect. Check with a nurse or doctor immediately if you start to experience any of the following side effects:

  • Chills
  • Difficulty breathing
  • Severe drowsiness
  • Fainting
  • Fast heartbeat
  • Fever
  • Flushing or redness of the skin
  • Severe headache
  • Nausea or vomiting
  • Skin rash, hives, or itching
  • Stomach pain
  • Swelling of hands, throat, or feet

These are rare side effects that should be immediately brought to the attention of a medical professional. Side effects other than those listed can sometimes occur in some patients, and should be shared with a doctor or nurse as soon as possible. You can call your doctor for advice about side effects, or report them to the FDA at 1-800-FDA-1088.


The dose that is used for a diagnostic test will be different depending on a patient’s size, health, and medical history. Your doctor will determine the appropriate dose for you. The amount of radioactivity in a dose is stated in the units of megabecquerels or curies. The dose you are administered can range from 0.185 megabecquerels (5 microcuries) to 1295 megabecquerels (35 millicuries). This dose will expose a patient to a similar amount of radiation as that of an x-ray.


Your doctor should know about any and all medications that you are taking, regardless of whether they are prescription or over-the-counter. There is a chance that they could interfere with the function or accuracy of the radiopharmaceutical test.

Eating food or using alcohol or tobacco around the time of your radiopharmaceutical test could cause interactions with the function of the test. Make sure you discuss with your doctor whether you should abstain from food, alcohol, or tobacco before your diagnostic test.


Before receiving a dose of radiopharmaceuticals, you should make sure your doctor is aware of all of your allergies. This includes allergies to medications, but also any other allergies, such as allergies to food dyes, animals, or preservatives.

Radiopharmaceuticals are not recommended for pregnant women. Be sure to tell your doctor if you are pregnant. Your doctor may choose to go ahead with a radiopharmaceutical diagnostic test anyway, but may reduce the dosage in order to minimize the radiation exposure to the fetus. This is of particular importance if you’re being administered radiopharmaceuticals that contain radioactive iodine. Radioactive iodine can enter the fetus’s thyroid gland and can cause damage to the fetus’ thyroid. Make sure you discuss your pregnancy and the risks and benefits with your doctor before receiving the test. Determine with your doctor whether the benefits are worth the risks of receiving the test.

It is possible for radiopharmaceuticals to pass from a mother’s body into her breastmilk. If you are breastfeeding, discuss this risk with your doctor. It may be necessary for you to stop breastfeeding for a certain period of time after receiving the test to minimize the risk of passing radiation to your baby.

Radiopharmaceuticals taken orally for diagnostic tests are generally present in such small amounts that they do not require special precautions. However, it is possible for radiopharmaceuticals to accumulate in the bladder. Your doctor may tell you to drink extra fluids or urinate frequently after the test to prevent this.

For patients receiving radioactive iodine (ask your doctor if your test includes radioactive iodine) :

  • Make sure that you tell your doctor if you are planning to have any future thyroid tests. Even weeks later, the results of the thyroid test may be compromised by the iodine solution you’re administered as part of your radiopharmaceutical test.
  • Radiopharmaceuticals can be used in diagnostic tests on children. The level of radiation is low enough to be considered safe for administration to children. However, it is important that you discuss with your doctor the benefits and risks of using a radiotherapeutic diagnostic test for a child.
  • Many medicines have not been specifically tested on elderly people. It is not known if they might affect elderly people in different ways than younger people. Radiopharmaceuticals are considered safe for administration to elderly people, and problems would not be expected to occur. However, since their bodies may react differently than that of a younger adult, it is important to monitor any unusual side effects experienced. Older adults may require additional monitoring before or after receiving a radiopharmaceutical diagnostic test. For example, certain radiopharmaceuticals may require people to have their kidney function monitored before and after the diagnostic test.


Radiopharmaceuticals are radioactive agents that are taken orally to diagnose certain diseases. Although these drugs are radioactive, the dosages are so low for use in diagnostic tests that radiation levels are at a low enough level to be safe. Radiation from a radiopharmaceutical diagnostic test is comparable to, or even lower than, the radiation that a patient would receive from the administration of an x-ray of the same organ.

For this reason, the risks of using radiopharmaceuticals for diagnosis are fairly low, especially when weighed against the benefits. Radiopharmaceuticals allow a nuclear medicine doctor to look at images of a patient’s internal organs in order to determine if they are healthy or present a medical condition.

Radiopharmaceuticals are generally not recommended for use by pregnant women, although there are cases when a doctor will determine the benefit to be high enough to justify the risk. It is important to discuss this with your doctor before making a decision.

Breastfeeding mothers should also talk to their doctors before receiving radiopharmaceutical tests. It is possible for radiation from the radiopharmaceutical to enter the breastmilk and be fed to the baby. Your doctor may tell you to abstain from breastfeeding after the test.

It is generally considered safe to use radiopharmaceuticals for diagnosis of children or elderly people. Radiation levels are low enough to be safe for children. While elderly people are not expected to experience any issues with radiopharmaceuticals, they should monitor any side effects and report them to their doctor or medical professional. It is always recommended that you discuss with your doctor whether the benefits of a procedure or medication are worth the risks inherent in any medical procedure or medication.

Special preparations for the test may be necessary. Make sure you understand any preparation instructions you receive, and talk to your doctor if you do not receive or do not understand the instructions. Failing to prepare may render the test inaccurate.

Interactions and side effects of radiopharmaceuticals are uncommon. Your doctor should be made aware of any allergies you have or other drugs you are taking, as well as your alcohol and tobacco use. Any of the listed side effects should be immediately reported to a medical professional.


Last Reviewed:
February 01, 2018
Last Updated:
January 27, 2018
Content Source: