Hormone therapy and depression

I started on 20 mg tamoxifen, by 3 months had very low motivation, brain fog? depression? Stuck it out for another 3 months but by then was having headaches 24/7. Other side effects not so bad, some warm flashes and difficulty cooling off after overheating in weather, some moodiness.
I was postmenopausal 69 at that time, DCIS, surgery, radiation.
I dropped to 5 mg and it was like night and day. Motivation quickly returned - I was so grateful, I signed up for guitar lessons and started TaiChi. No headaches.

Important note! I’ve found my regular doctors (general practice, endocrinologist, gynecologist) defer to the oncologist and will not question the medication dose or suggest that it might be causing my issues. They say, cancer treatment comes first. Yes. But. If it means going on other meds then I think they HAVE to be part of the equation to decide priorities.
When I saw my general MD about the headaches, she went through the possibilities for causation, testing everything that might cause headaches including a brain MRI and could find nothing. She said I should tell the oncologist of her findings. The oncologist, and the cancer neurologist who reviewed the MRI, said headaches were most likely from tamoxifen and my dose was lowered.
The problem with depression, or brain fog that I had, is its much more difficult to pinpoint a cause. Often drugs are used because they have nothing else that works. I was told I could try an anti-depressant.

About AI or tam:
Oncologist said I had a choice of tamoxifen or AI. AI’s do show a better response, but when you read the research the “significant” number is very small.

I’ve been on tamoxifen for 3.5 years. Was told by survivorship doctor that in Dec 2026 when the San Antonio Breast Cancer Symposium research has been presented, protocols will probably change, it will most likely be recommended that I can stop tamoxifen. Latest research is showing that for the cancer I had, DCIS ER/PR+ luminal A, three years has been shown to be as effective as five.

Also, the latest research is showing that while 20 mg of tamoxifen is preferred dose, 5 mg provides the same results for postmenopausal women with certain cancers, with less side effects.

A good question--and maybe ask oncologist too. I've been on letrozole for almost four years without any side effects. No depression or mood swings. But many women do have side effects. Do you have any routines or other things that can help with the depression that aren't medication? I will add that since the cancer diagnosis I exercise every day, am in psychotherapy, and keep a journal. These things might have helped my mood. A friend of mine is in a breast cancer support group which has really helped here. I've needed support, and sought it out.

@mir123 Thanks for your response. I have a very reliable, healthy routine. I do t feel stressed about my cancer diagnosis; I got good treatment and understand the risks of possible recurrence but am not worrying about that. This is a distinct change since starting the med. I’m due to speak with my oncologist soon and will raise it with her

@triciaot Thanks. This is helpful. I’ve been wondering about whether a lower dose would help. My cancer this time was invasive and also Luminal B so there is a bit more concern about distant recurrence. I need to balance all the hard choices (as we all do!)