Thyroid UK
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"Interactions that result in changes of levothyroxine binding in blood"

I was looking for something else when I came across this extract from the link below and immediately sent it to my daughter, who couldn't understand why she'd been feeling so bad and seemed to have gone back into hypothyroidism since taking HRT for the last few months. Her doctor hadn't a clue when she put her on it ! ! :

"Interactions that result in changes of levothyroxine binding in blood

Thyroxine-binding globulin (TBG) is a protein that binds to and carries thyroid hormone in the bloodstream. When the level of TBG is high, levothyroxine is trapped in the bloodstream and cannot get into the tissues where it is needed. If the thyroid is functioning properly, it will compensate for this by producing more thyroid hormones. But if the thyroid is impaired — as is the case for most people taking levothyroxine — an increase in TBG induced by another drug may produce symptoms of hypothyroidism because the thyroid can not produce more hormone.

Estrogens increase TBG, and women who are taking them at the same time they are on levothyroxine may need to increase their dose of the latter. Transdermal estrogen replacement (via patch) does not have much effect on TBG, so this may be preferable for women taking levothyroxine. Oral contraceptives containing estrogens (whether oral or via patch) increase TBG and may increase a woman’s levothyroxine requirements. "

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They had a nice chart which may or may not copy well. Thanks for finding the link. PR

Table. Drugs that interact with levothyroxine

Interactions that result in reduced levothyroxine absorption


calcium carbonate (TUMS)

calcium carbonate and magnesium hydroxide (ROLAIDS)


aluminum hydroxide (AMPHOJEL)

iron supplements

ferrous sulfate (FEOSOL, SLOW FE)


cholesevelam (WELCHOL)


raloxifene (EVISTA)**

sevelamer (RENAGEL, RENVELA)

sucralfate (CARAFATE)**


ciprofloxacin (CIPRO)

levofloxacin (LEVAQUIN)**

lomefloxacin (MAXAQUIN)**

moxifloxacin (AVELOX)*

norfloxacin (CHIBROXIN, NOROXIN)**

ofloxacin (FLOXIN)**

Grapefruit Juice

Interactions that result in increased levothyroxine metabolism, lower levels of in the blood


carbamazepine (CARBATROL, TEGRETOL)

oxcarbazepine (TRILEPTAL)

phenobarbital (LUMINAL, SOLFOTON)**

phenytoin (DILANTIN)

primidone (MYSOLINE)


efavirenz (SUSTIVA)

nevirapine (VIRAMUNE)

rifabutin (MYCOBUTIN)


St. John’s wort


imatinib (GLEEVEC)

sertraline (ZOLOFT)**

Interactions that result in changes of levothyroxine binding in blood


Interaction that results in increased or decreased levels of other drugs

warfarin (COUMADIN)

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But HRT that just returns levels to what they ought to be (physiological doses?) or were before they dropped shouldn't cause problems unless taken at the same time as levo (or all pre menopausal women would be hypo).


Our own oestrogen is natural though not horse wee or God knows what else.... And as above. "if the thyroid is impaired — as is the case for most people taking levothyroxine — an increase in TBG induced by another drug may produce symptoms of hypothyroidism because the thyroid can not produce more hormone."

It had definitely caused my daughter big problems and her GP should have known....let's hope patches work better.


Or she could try bioidentical hormones. I read an article today (from the Clymer Healing Center who deal with CFS) that reckons that menopause with symptoms is triggered by adrenal problems. Don't have the link unfortunately but should be available out there somewhere.

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Thank you. Will have a look for it.


CFS is not an actual Disease, but rather a handy catchall name, given to a set of symptoms, from another cause. I have every symptom on the list am Hypothyroid and have an auto immune disease that caused it.. Hashimoto's Disease., which has all the same symptoms of CFS and Fibromyaligia. See what i mean.


Hi Faith. Have you tried supplementing with B12 and high dose Vit. D?

Sorry, I'm obsessed with B12 since it gave my sister back her life after years of ME/CFS.


Thanks for trying. My b12 was way over range and D3 is normal way up in range after years of supplementing. My d was 14 and iron like it all way up and felt no different.


My sister's B12 was over 1000 - here is an extract from Sally Pacholok's book, "Could it be B12?":

"we believe that the 'normal' serum B12 threshold needs to be raised from 200 pg/ml to at least 450 pg/ml because deficiencies begin to appear in the cerebrospinal fluid below 550".

"For brain and nervous system health and prevention of disease in older adults, serum B12 levels should be maintained near or above 1000 pg/ml.

All the latest guidelines recommend treating symptoms as the tests, in any case, are flawed and unreliable.


my b12 was 1800


Indeed, CFS is a collection of symptoms, but in the US it is a very specific diagnosis. Clymer Healing concentrate on adrenal support.


I realise this may not work for everyone but I have been struck by how many people with ME/CFS are vegetarians or vegans, and they are also one of the groups most vulnerable to B12 deficiency, as are those with Crohn's or low stomach acidity, taking PPIs, which are among many other medications that deplete B12, people over 60, etc. etc.

Also, Autoimmune thyroid problems, B12 and D deficiencies are usually interlinked (my sister has severe B12 def. & we both have autoimmune thyroid disease) and they impact on all the systems of the body, especially the thyroid - it is more than possible that adequate B12 treatment may improve a thyroid problem.

Doctors are generally not up to date with the latest research guidelines on diagnosis and treatment for B12 deficiency and you have to be prepared to research and fight your corner or self treat as, I've already mentioned, the serum B12 tests are seriously flawed and unreliable.

You would have to have seen how ill my sister became before B12 injections gave her back her life.


for me it is all about this autoimmune disease and inflammation..i don't believe in the adrenal support stuff. Hypo's usually have low cortisol, low adrenal function that improves with proper thyroid treatment, also you can't make Cortisol without the signal from the Pituitary to make one mentions Pituitary. Pituitary issues are more common than Addisons, yet it is overlooked.


Dr S used to say that treating the thyroid would sort out the adrenal problems, while Dr P insists that you should sort out adrenal problems first. There doesn't seem to be any consensus. Dr Malcolm Kendrick seems to suggest that cortisol levels are very important to health. Personally, I find adrenal support very useful, as well as Paul Robinson's CT3.


Know what you mean. Daughter and sister were treated by Dr Skinner, who I'm eternally grateful to for free advice when I went with them! He advised me to ask GP for an increase in Levo dose and I only then began the journey towards health, resisting surgery' s frequent attempts to decrease it! We all had different needs.


What do you use for adrenal support?


Currently Adrenergize and Ashwaghanda.


thank you.


Our whole family take Ashwaghanda!


How coincidental! I've been having a think about tbg and oestrogen today, wondering if it's an issue within me at the moment.

Off to peruse :)

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The pill triggered my hypothyroidism or uncovered it, and IT got progressively worse each time I went back on it.

I'm trying to work out if there are correlations in the natural cycle and or lactation?


Hormones are such a delicate balance...hope you find your answers...


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