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Thyroid UK
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Was hyper now hypo

Hi, after being started on carbimazole just two weeks ago I had a blood test last week at endo.

Urgent phone call Monday to stop using carbimazole and come get levothyroxine.

Get a letter today to say tsh of 102 and free t4 of 4.5, 6 weekly tfts with up titration by 25mcg. Now in 100mcg

I feel better though than I did just two weeks ago.

Anything I should be doing?

8 Replies


You were hyperthyroid with TSH <0.05, FT4 28.6 and FT3 8.8 a few weeks ago but you were either horribly overmedicated on 20mg Carbimazole or you had an autoimmune flare up (Hashimoto's) which can cause transient hyperthyroidism. There is absolutely no doubt that you are overtly hypothyroid now with such high TSH and low FT4. 100mcg Levothyroxine will raise FT4 and FT3 and reduce TSH. Make sure you do have the next thyroid test in 6 weeks as dose may need adjusting either way. Arrange an early morning and fasting (water only) blood draw when TSH is highest, and take Levothyroxine after your blood draw. Ask your endo to test thyroid peroxidase and thyroglobulin antibodies to confirm or exclude Hashimoto's when you have your next TFT.

For maximum absorption Levothyroxine should be taken with water 1 hour before, or 2 hours after, food and drink, 2 hours away from other medication and supplements, and 4 hours away from calcium, iron, vitamin D supplements, magnesium and oestrogen.

It takes 7-10 days for Levothyroxine to be absorbed before it starts working and it will take up to six weeks to feel the full impact of the dose. Symptoms may lag behind good biochemistry by several months.



Thank you, all noted.

The only other medication I take is anastrozole, to suppress oestrogen due to breast cancer 3.5 years ago. Would this be safe to take with levothyroxine then? Am taking levothyroxine first thing and tend not to eat until mid morning anyway.

My pulse is and always has been low (40-60) so should keep a close eye right? Am assuming as only recently hypo I am being spared symptoms for now?



Take Anastrozole at least 2 hours away from Levothyroxine.

Low pulse/heart rate is a typical hypothyroid symptom but if it has always been low it may be natural for you.


Hard to tell at this stage whether your hypothyroidism is Carbimazole induced or due to a catastrophic collapse of your thyroid gland. Sudden onset hypothyroidism can be asymptomatic and now you are being treated and monitored you may be spared symptoms permanently.


Thank you, I'll take anastrozole at night then from now on.

Much appreciated.


The implication of the paper linked below is that anastrozole has no effect on thyroid or thyroid hormone levels. As always, though, I think you are right to take it physically separately as so many substances affect thyroid hormone absorption - including many ingredients (excipients) not just the active ingredients.

We unlikely ever to see complete evaluation of the effects of most medicines, in all their formulations, when taken at the same time as thyroid hormones. The only sensible answer is what you are doing.



One more thought.....in an effort to feel better I recently went back to a gym which I think has also helped me. Anything I should be careful of as I'm mostly doing cardio?


I'm taking a different drug to you after breast cancer but started going down hill I contacted the pharmacist at the cancer hospital. It she couldn't find any info to help but I have needed to up my NDT. From the start I took them approx 12 hours apart but if you look at the Thyroid Uk site it does say that Tamoxifen which does the same thing alters the absorption of thyroid meds and suggest an increase. I relayed this back to the pharmacist on Thursday and she I think will be writing to them for references. If so I hope she will let me know and I'll pass it on.


Thank you, I'll check it out. I was on tamoxifen until just over a year ago but had developed polyps so was switched.


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