It is widely assumed that levothyroxine cannot result in an allergic reaction, whether anaphylaxis or somewhat less serious, simply because it is almost identical to what we ourselves produce.
Sometimes it is accepted that specific issues occur in a few patients but they are focussed almost entirely on the excipients. For example, whether a product contains lactose, or not. Even that issue gets dismissed on the basis that the amount of lactose a tablet contains is too small to be significant.
Some tablets contain around 50 milligrams of lactose. If the tablet is a 50 microgram dosage levothyroxine tablet, that is one thousand times as much lactose as there is levothyroxine.
Yet we are being told that the tiny amount of levothyroxine is vital. That even the tiniest increase could cause all sorts of problems. Yet a thousand times as much lactose cannot possibly be a problem!
This blog is a list of references to unusual side effects/adverse reactions to commercial levothyroxine products. There will be other reports and if you know of any, please let me know and I can add them.
Most reports of issues with levothyroxine are fairly simple - maybe feeling better on one that does not contain a specific excipient. Some cannot tolerate lactose. Some cannot tolerate mannitol. While some might never actually identify the source of their problems. These reports are far more serious.
In some cases, a change of make helped, in others, switching to liothyronine was successful. (Though the reports make it clear that using liothyronine is usually considered very unsatisfactory even when the alternative is appalling.)
Liver Injury Induced by Levothyroxine in a Patient with Primary Hypothyroidism
Occurrence of thyroxine tablet (Thyradin S(®)) - induced liver dysfunction in a patient with subclinical hypothyroidism.
Liver injury induced by levothyroxine tablets in a patient with hypothyroidism
7165 A Case of Severe Myxedema Coma with Levothyroxine Allergy
Journal of the Endocrine Society, Volume 8, Issue Supplement_1, October-November 2024, bvae163.1848, https://doi.org/10.1210/jendso/bvae163.1848
Published: 05 October 2024
https://academic.oup.com/jes/article/8/Supplement_1/bvae163.1848/7812238?login=false
A tale of two patients with hypersensitivity reactions to levothyroxine.
https://europepmc.org/article/MED/35080627
Successful Oral Levothyroxine Desensitization in a Patient with Severe Hypothyroidism Post Radioactive Iodine Therapy: A Case Report
https://europepmc.org/article/MED/34966208
A Bizarre Complication of Levothyroxine Therapy.
https://europepmc.org/article/MED/34660246
Self-Reported Allergy to Thyroid Replacement Therapy: A Multicenter Retrospective Chart Review
https://www.endocrinepractice.org/article/S1530-891X(20)36015-8/abstract
[i][b]helvella - Serious Issues from Levothyroxine[/b]
Some references to case reports, etc., of adverse reactions to levothyroxine tablets.
Last updated 10/02/2025[/i]
Link to blog:
https://helvella.blogspot.com/p/helvella-serious-issues-from.html
If you find anything incorrect, misleading, typos, links that don’t work, etc., please let me know. Go to my profile and use the contact details there.
