I was told after surgery that tamoxifen was the best drug for me. The surgeon told me all about it then said I couldn't take due to a previous blood clot. I was offered zoladex and letrozole. My initial reaction was why bother if it's not as effective so I postponed my final decision until after rads.
My oncologist was happy for me to wait to make a decision, I asked him to run all the options through his computer based on my individual details, the percentages for zoladex and letrozole were only slightly behind tamoxifen. Every doctor I have been treated by has assumed I would be on tamoxifen, gp's and surgeons, I think it's just the standard treatment. But you don't have to take it. Discuss your worries with your oncologist. Get them to check your figures, get the AI leaflets from here, then you can make a more informed decision.
We have the last say on our own treatment.
Perhaps you need to be asking your consultant this very question. If you are concerned you can choose not to take it until you have your answers. I suppose it is a case of weighing up risk to benefit, but at the end of the day it is your decision. If you are post menopause you could be offered an alternative, perhaps you could see your GP as well to discuss your options.
Hope you get answers quickly.