Hi Susan, I have been trying to find out about herceptin, tamoxifen and thyroxin interactions, and came across your post. I too have hypothyroidism, and have been on synthetic thyroxin (levaxin) since 2001.
I will also post this separate on the main forum
Went through chemo and radiation last year, been on tamox for 1 ½ yr, and finished my year of herceptin in May. My TSH has been getting lower and lower, and at the same time I have been feeling worse. Fatigue and depression, severe brain fog, muscle and joint aches i a. For me, typically hypo symptoms, but of course it could also be side effects from the bc treatment. I believe that’s what the docs wanted to me to think it was. In sept last year I complained about this to my doc, she suggested anti-depressiva, and me to visit a psychologist. I refused any more drugs with side effects, but agreed to start in therapy
In February, after almost a year into tamox treatment I noticed the freeT4 was low even if the TSH was low. Increased my dose in spite of what the doc said. She was sooo afraid to let the TSH go below 0.2. Felt a bit better, but the depression and the brain fog was still there. Then I asked to measure free T3, and it was very low! Asked for synthetic T3 (here Liothyronin, think it is called cytomel in US) to combine w thyroxin, but my doc had never heard about it. After a lot of tears, she agreed to give me some, and as my T4 also was a bit low, I just added a small dose to the thyroxin dose. It is otherwise recommended to lower the thyroxin dose to avoid hyper symptoms.
After 3 days the brain fog went away! And the insomnia!
After 2 weeks the depression was gone!
My TSH is now 0.03, I have no hyper symptoms, but my mental state is still a bit unstable. However, the continual faint-heartedness I felt before starting on T3 meds is completely gone.
After searching I found that tamox interacts with thyroxine. My onc never told me this, even when I asked, and talked about getting off it. (I don’t have the link to what I found, my husband got hold of it through the university archive. I will post the abstract.) And who knows, Herceptin might be doing the same. There just haven't been any studies about it...
I still have aches, fatigue, and some headaches, and I guess it’s the herceptin. I believe my body is drained from all the chemicals and synthetics I have taken the last years, and I’m doing what I can to detox. But that’s another story and another post
