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Arimidex Does it affect TSH and /or thyroid level ?


Hello, I have not posted in a long time but when I am looking for an answer to a question I often come to Breast Cancer Org. I am a "retired" nurse and I have learned more from my breast cancer "sisters" than from other sources. I have been on Arimidex for 4 years minus 6 weeks, I am on an Arimidex "vacation" until my cardiologist and I can begin to figure out a way to manage my BP while on Arimidex or If it will be possible. My BP became elevated quickly. I have been struggling to get my TSH level back to normal for more than 6 months - it remains quite low while trying to get my Synthroid dose regulated. Any experience with aromatase inhibitors and TSH / thyroid  would be much appreciated. Of course, it is not reported anywhere.  Also, how long has it taken for Arimidex to "wash out" after you have stopped taking it for a short time or permanently ?    I am so grateful that you are here for me and all of us. My husband died very suddenly in November, 2009, and it has been a difficult bereavement journey. I was not quite 2 years out from the diagnosis of my second Primary Breast Cancer.



  • Megadotz
    Megadotz Member Posts: 13
    edited February 2012


     I'm on Femara and have had some issues getting my thyroid levels regulated since chemo and hormone therapy.  I also have Hashimoto's thyroiditis -- discovered after a thyroid cancer scare.

    The drug information says that the AI doesn't affect thyroid levels for healthy patients.   Doesn't make any claims for those of us who have existing thryoid levels.

    Estrogen and thyroid are hormones that  interact with each other.   During menopause, I took HRT and needed to have my sythroid adjusted upward.   With the AI, the endocrinologist had to take it down a couple of levels until  things became stable.

    I ended charting my TSH levels/synthroid dosage for the endo with notations showing that the TSH was higher durning chemo, and  low once I started Femara. It helped put in perspective for the endo.

    It takes about 2 months to see changes in TSH if you change dosages, it my take that long to see the difference of stopping the AI.

    Good luck.  It's apain to get this straightened out. 


  • otter
    otter Member Posts: 757
    edited February 2012

    Hi, porchchair,

    I have Hashimoto's thyroiditis. It was dx'd about 7 years before my BC dx, and I'd probably had the thyroid problem a lot longer than that.  So, I went through the roller coaster ride to get my thyroxin dose stabilized way back then.

    "They say" menopause can change our thyroid function, or at least it can change the amount of thyroxin we need to take if we're hypothyroid. I don't know if that was true for me -- all of that happened at about the same time as some other stuff was going on, so there's no way for me to know what was affecting what.

    My thyroxin dose had been stable for quite awhile, though, before my BC dx. I do think chemo screwed things up (I don't remember which direction), but I asked my PCP to hold off and not adjust my thyroxin dose while I was on chemo.  Sure enough, things calmed back down once I'd recovered from the 3 months of chemo. 

    It makes sense that chemo would alter thyroid activity in those of us with Hashimoto's, or probably with any type of thyroiditis, because chemo drugs have powerful antiinflammatory effects.  My med onco said her patients with arthritis or other inflammatory diseases often go into remission (fewer symptoms of their inflammatory disease) while they're on chemo, and then relapse (symptoms come back with a vengeance) after the chemo is over.

    I don't know whether Arimidex affects thyroid function all that much, though.  (YMMV.)  I've been taking Arimidex/anastrozole for almost 4 years, and my TSH and thyroxin dose haven't changed during that time.  My PCP thinks my TSH is a bit too high, so he wants to tweak my thyroxin dose upward a notch... but my onco and my osteoporosis doc would like my TSH to be ever so slightly higher than it is, because they're worried too much Synthroid will affect my bone density.<sigh>

    I figure that means it's a draw.  And, yes, it does take 6 to 8 weeks to see a change in TSH when something is done to alter it.


  • CinD
    CinD Member Posts: 13
    edited September 2013

    I was wondering if anyone has any new information on mixing A.I.s/Tamoxifen with Synthroid.  While taking Tamoxifen, my thyroid function improved and I was able to lower my dosage.  Since being on A.I.s the past 8 months, my thyroid numbers have been all over the place. 

    I can't find any information on whether it is better to take Tamoxifen or an A.I. when also taking Synthroid.  It just seems like there is great potential for all types of things to get screwed up when we're throwing two pills in our systems that play with our hormones. Has anyone spoken with an endocrinologist about this?  My family physician monitors my thyroid function, but she's not a thyroid specialist.  I see my oncologist next month and will ask him.

    Any information or general thoughts are appreciated.

  • gsg
    gsg Member Posts: 1,700
    edited September 2013

    Hi.  I have been on Arimidex and Synthroid since 2006 and did ask both my endocrinologist and oncologist about mixing the two.  They told me no problem but to take one at night and one in the morning, so I take synthroid in the A.M. and Arimidex in the evening.  My TSH levels are always good and I've remained cancer free for 7 years now with no side effects from Arimidex other than hot flasses, so it's working for me.    Hope this helps and thatyou get your numbers to settle down.

  • metoo1
    metoo1 Member Posts: 1
    edited October 2019

    I too was wondering about this. I am on Anastrozole for 1 year already (4 more to go) and all of a sudden I have Hypothyroidisim? I am very active and although there is a history of thyroid cancer in my family, I have never had any issue with it until I started taking Anastrozole. The research says the drug doesn't have an affect on the thyroid but the thyroid too is a hormonal gland and Anastrozole treats hormones level so wouldn't it make sense that it would affect it? So far the endocrinologist didn't give me any drugs for it because he said it is slight but for how long would it stay slight? my arthritis is definitely way worse and I have constant joint pain since starting the Zometa injections (I have 4 more to go - 6 altogether)

    This sucks big time ya know:(? I have always been healthy and happy, exercise daily, eat healthy food, never smoked, never drank, never did drugs, have no BC history in my family and then this. I am lucky that I have found the little ball in my breast and although the silly dr. who replaced my regular dr. insisted that it is "just a fibroid" and it's "normal at my age", when the mammogram nurse called me for another one and then ultrasound and then biopsy, that silly dr. told me to "trust him it's nothing", only it turned out to be stage 1 bc with 2 lymph nodes affected. Lucky for me, my regular dr. came back. I had the surgery and 25 radiation sessions and now on Anastrozole.

    So now this thyroid things has come up.

    You wonder what's next eh?

  • moderators
    moderators Posts: 7,928
    edited October 2019

    metoo1, we want to welcome you to our Community here at BCO! We hope you find the support and information you're looking for.

    This is an old thread and nobody posted here since 2013, so it's unlikely you'll hear back from any of the original participants. Perhaps bumping the topic with your post will catch the attention of any other member who can offer advice. Anyway, if you want you can start your own new conversation to share your particular situation. Under this same forum should be fine. Just click above this page, in the title of the forum, and then click on "Start a new topic". Add a title, write your comment, and when you are ready to post your new topic, click "Submit".

    We hope this helps!

    The Mods