Last update: May 28, 2019

Iodine 123

High Risk for breastfeeding

Poorly safe. Evaluate carefully.
Use safer alternative or interrupt breastfeeding 3 to 7 T ½ (elimination half-lives).
Read the Comment.

Radioactive iodine is concentrated in thyroid and breast milk and may suppress thyroid function in infants.

The I-123 is used as a diagnostic agent. Its mean physical radioactive lifetime is 13.2 hours (Howe 2008) and the half-life of biodegradation is 4.8 to 10.2 hours (Stabin 2000). After 10 physical half-lives (66 hours), the element ceases to have significant radioactivity and after 5 biological half-lives (51 horas) its concentration in the milk is negligible.

If you want to limit exposure to 0 mili Servers (mSv), you should stop breast-feeding for a period equivalent to from 5 to 10 biological half-lives. It is also possible to determine the radioactivity in milk samples.
Since the annual natural background radiation we receive is around 6 mSv, for a more conservative approach we should wait just long enough to achieve an infant exposure of less than 1 mSv (0.1 rem)

The iodine-123 that is administered to nursing mothers must be pure, that means, without containing traces of I-124 and I-125 (Mitchell 2019).

Recommended time for transient weaning to ensure reducing exposure to 1 mSv:

I-123 as sodium iodine hippurate or orto-iodo hippurate (123 I-OIH): Doses up to 100 MBq (4 mCi) waiting time= 8 to 12 hours. According to Nuclear Regulatory Commission of the United States: it is not necessary to stop breastfeeding.

I-123 as sodium iodide (123 I-NaI). If uncontaminated with I 125: doses up to 20 MBq (0.5 mCi) waiting time= 3 to 6 hours. If contaminated: ICRP (Mattsson 2015, Sachs 2013, ICRP 2008): > 3 weeks, The American Thyroid Association (Alexander 2017 Q91 R77): 3 to 4 days

I-123 as iobenguane (I-123 meta-iodobenzylguanidine, I-123-MIBG). If uncontaminated I 123, discontinue breastfeeding for 12, 24 or 48 hours depending on whether the dose was 150, 370 or 400 MBq (4, 10 or 11 mCi). With contamination of I 124 or I 125, the interruption period is >3 weeks (Sachs 2013, ICRP 2008).

I-123 as ioflupane: Stop breastfeeding from 1 day (Society of Nuclear Medicine, Djang 2012) to 6 days (the manufactured).

I 123-Labeled Human Serum Albumin (123 I-HSA): > 3 weeks (Sachs 2013, ICRP 2008).

I 123-Iodofiltic Acid (beta-methyl-15-(4-iodophenyl) pentadecanoic acid; I 123 BMIPP): > 3 weeks (Sachs 2013, ICRP 2008).

I 123-phenylpentadecanoic acid (123 I-IPPA): > 3 weeks (Sachs 2013, ICRP 2008).

For more safety, you can request to measure the amount of radioactivity of the milk in the nuclear medicine service.

If you want to continue breastfeeding, extraction and storage of breast milk in a freezer for days or weeks must be previously ensured. During the suggested days for interruption of breastfeeding after the test is done, the child can be fed exclusively with the milk previously stored or using both breast milk and formula.
After the test you can continue extracting and storing the milk in a separated freezer for 10 physical half-lives (132 hours = 5.5 days, once radiation is gone and it can be used for feeding the baby).

Mothers receiving a dose as lower as 400 MBq for a thyroid scan are not in need to refrain from close contact with their children.


Suggestions made at e-lactancia are done by APILAM´s pediatricians and pharmacists, and are based on updated scientific publications.
It is not intended to replace the relationship you have with your doctor but to compound it.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.


Main tradenames from several countries containing Iodine 123 in its composition:


Variable Value Unit
Oral Bioavail. 100 %
T1/2 radiol: 13,2 hours
M/P ratio 25 -


  1. ARSAC: Administration of Radioactive Substances Advisory Committee. Notes for Guidance on the Clinical Administration of Radiopharmaceuticals and Use of Sealed Radioactive Sources. Section 7 Conception, Pregnancy and Breastfeeding, p. 47-53. ARSAC Support Unit. Centre for Radiation, Chemical and Environmental Hazards. Public Health England. 2019 Abstract Full text (link to original source) Full text (in our servers)
  2. Mitchell KB, Fleming MM, Anderson PO, Giesbrandt JG; Academy of Breastfeeding Medicine.. ABM Clinical Protocol #30: Radiology and Nuclear Medicine Studies in Lactating Women. Breastfeed Med. 2019 Jun;14(5):290-294. Abstract
  3. Alexander EK, Pearce EN, Brent GA, Brown RS, Chen H, Dosiou C, Grobman WA, Laurberg P, Lazarus JH, Mandel SJ, Peeters RP, Sullivan S. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017 Abstract Full text (link to original source) Full text (in our servers)
  4. US.NRC - Nuclear Regulatory Commission Office of Nuclear Material Safety and Safeguards. Apéndice U, Tabla U.3. Consolidated guidance about materials licenses. Program-specific guidance about medical use licenses. Draft Report for Comment. Appendix U, Table U.3. NUREG-1556. Vol.9, Rev 3. 2016 Full text (link to original source) Full text (in our servers)
  5. Mattsson S, Johansson L, Leide Svegborn S, Liniecki J, Noßke D, Riklund KÅ, Stabin M, Taylor D, Bolch W, Carlsson S, Eckerman K, Giussani A, Söderberg L, Valind S; ICRP.. Radiation Dose to Patients from Radiopharmaceuticals: a Compendium of Current Information Related to Frequently Used Substances. Ann ICRP. 2015 Abstract
  6. Sachs HC; Committee On Drugs. The transfer of drugs and therapeutics into human breast milk: an update on selected topics. Pediatrics. 2013 Sep;132(3):e796-809. Abstract Full text (link to original source) Full text (in our servers)
  7. Djang DS, Janssen MJ, Bohnen N, Booij J, Henderson TA, Herholz K, Minoshima S, Rowe CC, Sabri O, Seibyl J, Van Berckel BN, Wanner M. SNM practice guideline for dopamine transporter imaging with 123I-ioflupane SPECT 1.0. J Nucl Med. 2012 Abstract Full text (link to original source) Full text (in our servers)
  8. Bombardieri E, Giammarile F, Aktolun C, Baum RP, Bischof Delaloye A, Maffioli L, Moncayo R, Mortelmans L, Pepe G, Reske SN, Castellani MR, Chiti A; European Association for Nuclear Medicine. 131I/123I-metaiodobenzylguanidine (mIBG) scintigraphy: procedure guidelines for tumour imaging. Eur J Nucl Med Mol Imaging. 2010 Abstract
  9. ICRP. Radiation dose to patients from radiopharmaceuticals. Addendum 3 to ICRP Publication 53. ICRP Publication 106. Annex D. Recommendations on breast-feeding interruptions, p. 163-165. Ann ICRP. 2008 Abstract Full text (link to original source) Full text (in our servers)
  10. US.NRC - Howe DB, Beardsley M, Bakhsh S. U.S. Nuclear Regulatory Commission Office of Nuclear Material Safety and Safeguards. Apéndice U, Tabla U.3. Consolidated guidance about materials licenses. Program-specific guidance about medical use licenses. Final report. Appendix U, Table U.3. NUREG-556. Vol.9, Rev 2. 2008 Full text (link to original source) Full text (in our servers)
  11. Stabin MG, Breitz HB. Breast milk excretion of radiopharmaceuticals: mechanisms, findings, and radiation dosimetry. J Nucl Med. 2000 Abstract Full text (link to original source) Full text (in our servers)
  12. Mountford PJ, O'Doherty MJ. Exposure of critical groups to nuclear medicine patients. Appl Radiat Isot. 1999 Abstract
  13. Stabin MG. Health concerns related to radiation exposure of the female nuclear medicine patient. Environ Health Perspect. 1997 Abstract
  14. Wilkinson LE, Heggie JC, Booth RJ. Secretion of [131I]iodide in breast milk and infant dosimetry resulting from the administration of [131I]meta-iodobenzylguanidine. Eur J Nucl Med. 1995 Abstract
  15. Kettle AG, O'Doherty MJ, Blower PJ. Secretion of [123I] iodide in breast milk following administration of [123I] meta-iodobenzylguanidine. Eur J Nucl Med. 1994 Abstract
  16. Rose MR, Lawson RS. Excretion of radiopharmaceuticals into breast milk. Eur J Nucl Med. 1994 Abstract
  17. Rose MR, Prescott MC, Herman KJ. Excretion of iodine-123-hippuran, technetium-99m-red blood cells, and technetium-99m-macroaggregated albumin into breast milk. J Nucl Med. 1990 Abstract
  18. Fulton B, Moore L. Radiopharmaceuticals and lactation. J Hum Lact. 1990 Abstract
  19. Mountford PJ, Coakley AJ. A review of the secretion of radioactivity in human breast milk: data, quantitative analysis and recommendations. Nucl Med Commun. 1989 Abstract
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  21. Hedrick WR, Di Simone RN, Keen RL. Radiation dosimetry from breast milk excretion of radioiodine and pertechnetate. J Nucl Med. 1986 Abstract Full text (link to original source) Full text (in our servers)

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