Having taken both an A.I. (Anastrozole, for 7 months) and Tamoxifen (for 5 months) before going off everything on Aug. 30, 2023, I can report that Tamoxifen is easier to tolerate and does less bad stuff to you in regards to your mental brain fog, teariness, etc. It isn't "good" because I was so fatigued that I could not stay up for more than 3 hours The main side effects were a constant urge to pee, when I took a lower dose (10 mg., every other day, 40 per week). I had such a bad time on Anastrozole that I told him I would try Tamoxifen, but I was going to tip toe into those waters. I was "okay" on 40 mg. a week (10 every other day). Everything from the waist down felt dry and itchy, but I could have stood it (although I didn't feel "normal"). The worst thing, at that point, was having to always be within 5 minutes of a bathroom. The feeling of an urgency to urinate was always there, even if it was bogus. However, on June 23rd my oncologist called me up and said I had to take 20 mg. daily (140 weekly) because the only clinical data they had that it worked was for that amount and my reliance on the 700 women in the Italian Women's Study was comparing apples to oranges, as their tumors had been "in situ" and mine had broken through, so I stepped up taking the 20 mg. pill daily. From that point on I had constant UTIs, the severe exhaustion I mentioned, which was debilitating, and the aforementioned constant urge to urinate. I did not have any "mental" side effects on Tamoxifen. Anastrozole for 7 months was a whole other thing. Teariness. Mood swings. Blurry vision. Insomnia, Excruciating back pain and pain in my frail left knee joint. Dry skin. Dry eyes. Vivid violent nightmares And then (9/15/2022) my fragile left knee joint gave up and quit working. I had to go to a joint pain clinic and have shots (32 ml of an anti-inflammatory; 6 ml of Durolane; Tramadol for pain). I was in a wheelchair from September 15 of 2022 until March of 2023 and quit taking Anastrozole, which was a tentative protection against a recurrence. However, apparently the trade-off was me not being able to walk myself to the bathroom or walk anywhere else and that trade was unacceptable to me. I did face decisions on what to do about my damaged knee. We were en route to Texas for the winter. The doctors in Illinois said they could give me an MRI to pin down exactly what had happened to my left knee, but then what? What did I want to do about it? It felt just like a meniscus tear and I was hobbling with a cane or being wheeled to my first post-operative mammogram on October 3rd (NED). I am now off all adjuvant therapy and have the opinion of 2 Texas oncologists that a woman who had been placed in a clinical trial for bad arthritis and had a badly damaged left knee joint was a bad candidate for A.I. drugs, since they are known to inflame previously injured or arthritic joints. It was, honestly, the worst pain I have ever endured in my then-76 years of life. I was denied an oncotype initially in Illinois ("You don't need one.") My Texas doctor got me my onco score and it is 29, which should have meant chemo at the outset. However, it was now 17 months past surgery. I had been off the Anastrozole for 9 months and was feeling normal again. I was talked into trying Tamoxifen and did so for 5 months. It is worth noting that, on March 7, my blood work before I got heavily into the Tamoxifen was normal. On Aug. 30, when I called in in distress and had further blood work, 10 things were not normal. If I had to select an A.I. drug to take and had any choice, I would ask for Exemestane, which seems to be tolerated better than the other 2. However, someone who was having regular and frequent MRIs of her left knee while in the MOST study from 1997 to 2020 should not have been given any of the 3 main A,I.'s. If you are a person with a family history of arthritis or any damaged joints, think long and hard before signing up for the pain you will experience taking an A.I. Tamoxifen is a better choice for an old person like me with a well-documented history of joint pain and issues.