How do you find the anti-estrogen therapy that's right for you?

Posted by mf915611 @mf915611, Apr 29, 2022

I have been on Anastrozole for four weeks. I have brain fog, joint pain and extreme fatigue. My Doctor wants to switch me to Exemestane.I am concerned with the side affects I have read about it. Hair loss ,bone pain,stomach pain,etc. Is there a better drug with less side affects?

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Hi Mf9156611! I have the same issues and side effects as you have. I’ve been on Anastrozole, Tomoxifin, and currently I’m on Exemestane . I have had side effects with each of these. The Anastrozole caused brain fog so severe I thought I was loosing my mind. My doctor switched me to Tomoxifin and I broke out in hives. It seems that there is something in it that I’m allergic to.

Again my doctor switched me to Exemestane, and I’ve been on it for two years now. It’s ‘ok’, but there is still some brain fog. I’ve done a lot of research and have found that it’s not so much the drug causing brain fog, but rather the lack of estrogen. Taking these drugs is like being in ‘permanent menopause’. As women, our bodies and brains, need some estrogen to function normally. I wish I could explain it better in medical terms. It’s truly frustrating, and very embarrassing. My husband and son make fun of me when I’m forgetful. It’s very hurtful, but for some reason they just don’t ‘get it’ even though my doctor has explained it to them. I’m so very grateful to this forum where I can express myself to other women who understand.

Best of luck to you as you continue on this journey. I suppose having brain fog is better than cancer! I’m very grateful that my cancer was found on a routine doctor visit and mammogram in an early stage 2.


I tried generic anastrazole and had trouble with fillers before I even did more than a week. I then tried generic letrozole. I ended up with brand name Femara (letrozole). My doc also said it would be fine to take alternate days, if that helped with side effects, but mine were tolerable and I stuck to daily.

The Femara insert contains a study that showed that 20% of the prescribed dose is effective so it should be okay to do alternate days, considering the half life of the drug and that 20% figure (I am speculating based on their own insert and my doc's approval of alternate days).

Here is more info on letrozole, which probably applies to others.
"Letrozole’s terminal elimination half-life is about 2 days and steady-state plasma concentration after daily 2.5 mg dosing is reached in 2-6 weeks."

So steady state plasma concentration takes awhile and that may explain why some are having more side effects after that period of time. Also, to me, it makes sense that 1) side effects might change over time with a hormonal med and 2) if we stick it out the body MIGHT adjust and stabilize....I have no studies on that but that was my experience and it makes sense.

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I am trying this drug now! Thank you for your info!

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