The oncologist initially discussed both tamoxifen and AIs with me. He was okay with my choice of tamoxifen because I have osteoporosis, -2.9 in two areas, prior problems with fasciitis (deQuervain’s in my hand and plantar fasciitis in my foot) and I am on the lower risk for ovarian cancer and thrombosis. It’s been 18 years since menopause so I’m someone that is assumed to have low estrogen, my body having adjusted to low estrogen by now. I believe that it is a bit unknown whether tamoxifen will be more of an agonist (promote estrogenic like response in other parts of my body besides my breasts) or have a more antagonist behavior (not estrogenic) in someone like me.

I’ve had a mixed bag response to tamoxifen. Prior to breast cancer, I had terrible vaginal atrophy. Tamoxifen reversed that (a blessing) - meaning it was behaving as an agonist, providing an estrogen-like response. I’ve had minor, very minor, issues with warm flashes and mood changes that resolve within 4 weeks - going on or coming off tamoxifen.
But I had headaches and brain fog, starting about 3 months into therapy. We tried a medication holiday, I’ve seen my general practitioner, to rule out other causes for the headache, had a brain MRI, and saw a neurologist. The consensus was that the headaches are probably caused by the tamoxifen.

I caution you with my next comments, because I’m not recommending you try this as there is not a body of research to support good outcomes. I lowered my tamoxifen from 20 mg, to 10, to 5 and didn’t see a change. Although I believe I didn’t wait long enough to see a difference. Tamoxifen stays in the system a long time.
Until yesterday, I had been taking 2.5 mg (not a recommended dose) and headaches and brain fog are gone. But vaginal atrophy has returned (not as severe, but definitely at an unacceptable level). So I went back up to 5 mg, not just because of the atrophy but 5mg is hopefully enough to be protective. I’m going to give it a 2-3 month trial to see if the headaches return. I think the oncologist will allow me to stay on 5 mg - but not sure. I have an appointment for my follow up this coming Wednesday so I’ll see what they say. I’m one year post surgery/radiation.
I’m pretty resistant to changing to a AI. I would maybe choose to take no hormone treatment if the only thing offered is an AI.
I want to review my personal risk of BC recurrence with the oncologist to help make a good decision! Wish me luck!