Hello,
I just wondered if anyone on thyroxine had had to raise their dose when on tamoxifen and roughly what the changes were?
I’m on 100 at the moment which is the lowest I’ve ever been on. Started tamoxifen nearly 2 weeks ago. I have a blood test booked but not for another 3 weeks.
Hi I am on 100 thyroxine and have stayed on the same amount during my time on tamoxifen (since June 2020) x
I had to increase my thyroxine dose from 75mcgs to 100mcgs daily after taking Tamoxifen for a few months. I’m due to have another check blood test. I believe Tamoxifen interferes with thyroxine & so this is common.
Hope that helps you. X
Hello, I’m on Thyroxine 100 mcg and started Tamoxifen in July. I had no idea tamoxifen interfered with Thyroxine. However I have been feeling tired but just put this down to radiotherapy which finished 25th August. Had a phone appointment with the breast nurse on Monday for follow-up after radiotherapy, but thyroxine wasn’t mentioned. I’m due my annual blood test for Thyroxine in November so will be sure to ask about this.
Take care K
Thanks all - it’s often very individual and it clearly is here.
I’ve been on it for 26 years. Oral oestrogen leads to me needing more as did pregnancy (a lot).
I know that tamoxifen can act in a similar way to oral oestrogen and some women need a tweak. But good to remain within range, around 0.8 to 1 tsh.
Exactly same for me- I had put it down to radiotherapy fatigue. It was my GP that mentioned my thyroxine may need tweaking & he was right & my tiredness improved greatly too. All the best to you. 
Thank you, do you mind me asking by how much?
Can’t tell if I’m feeling thyroidy or it’s the tamoxifen!
I had been on Thyroxine 75mcgs daily & it was increased to 100mcgs. X
Ok thanks. I hope things are easier for you now x