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Tamoxifen dosages - anyone with IDC do 5mg?

sl43sl43 Member Posts: 10

I recently got a hold of my doctor's notes for each follow-up I had with him since 2019. I reviewed everything, and saw how my dosing of Tamoxifen was all over the place. For intervals of a year or several months, I was taking 20 mg, 10 mg, or 10 mg every other day (effectively 5 mg). I did have some endometrial thickening that required a D&C, early on, and did have some insomnia and weight gain. These were inconveniences that I brought up to my onc at various appointments, just to keep him abreast; without my persuasion, he said it was no problem to reduce my dosage, and therefore at various times in the past 4 years, I have been taking Tamoxifen at various strengths, and for quite a long time was on as low as 5 mg.

May I ask for any accounts from any of you ladies who have discussed lower dosages with your oncologists and what they told you? I've researched the topic online ad nauseum but maybe I missed something…? (I'm going blind from reading publications and abstracts.)

Thank you in advance!


  • cheftoast
    cheftoast Member Posts: 24

    I did 20mg for over a year, but developed such dire side effects that my MO had me go off it for several weeks, then restart at 10mg. I felt so great right before starting the 10mg, that confirmed I was doing the right thing by reducing. 10mg is indeed better — I still have crushing fatigue but less, the brain fog is less foggy, and the depression is manageable with effexor. But it’s still pretty disabling, so I asked about going down to 5mg.

    My MO said he was not comfortable taking me down below 10mg because there is not good data yet. Some research has been done on DCIS, but not for people who have already developed an invasive cancer. He was not willing to experiment with me. My risk is higher than average, but not BRCA-level high. So I’m sticking with 10mg and hoping the research catches up soon. Hope that helps!

  • sl43sl43
    sl43sl43 Member Posts: 10

    @cheftoast Thank you - yes, very helpful!! I am wondering why my onc was willing to let me go down so far to 5mg based on unavailable data - it's making my nerves jangled but I can't un-ring the bell…. I appreciate your input on this. I also know that Tamoxifen can be a burden for some - glad you were at least able to mitigate some of the SE's!

  • moderators
    moderators Posts: 7,685


    We know these two topics don’t apply directly to you, but might give you some insight on your doctor’s thoughts on the research. (And in plain easy to understand language!)

    we hope this helps!

    —The Mods

  • sl43sl43
    sl43sl43 Member Posts: 10

    @moderators 🙏 This was so thoughtful of you - thank you! Even though 5mg is good enough for non-invasive situations, I just hope it's potent enough to handle post-invasive disease… I was on low dose for quite a while - it's nerve-wracking. But thank you again - I DO find the information on very accessible and reader-friendly.

  • gardengurl
    gardengurl Member Posts: 23

    Hi there. I’ve been taking tamoxifen 20mg every other night (effectively 10mg daily) I had a low grade tubular bc . It’s highly estrogen + and rarely spreads but onc says they treat it same . I tried all 3 AI’s and tamoxifen 20mg daily but couldn't tolerate. My surgeon thinks I would be fine with 5mg daily but onc said that won’t work. In October I found lcis in “healthy “ breast after a reduction and lift. So I’m staying with the 20mg every other day along with daily exercise. More plant based diet and cut way back on alcohol. It’s the best I can do.

  • salamandra
    salamandra Member Posts: 725

    I'm not a professional in any of this, but based on my reading, this is my understanding.

    Research on tamoxifen (and many drugs) aims to find the highest tolerable dose rather than the lowest effective dose. I think this is for cost/efficiency reasons primarily, but also partly impacted by regulatory policies.

    The result is that we don't really know whether 5mg is just as effective as 20mg, but we do know that 20mg is much more tolerable than 40mg, for example.

    Still, 20mg ends up not really being tolerable for a lot of women. I think statistics show that something like 50% of women end up not fully compliant with tamoxifen treatment. That's surely not all due to tolerability (it would include women who are impacted by access to health care, or women who may have been able tolerate the dose if they had better supportive health care, and also and all other reasons not to stay on the drug), but a significant portion is.

    On these boards, I have read of many women, with the support of their doctors, experimenting with lower dosing to see if it helps them stay on tamoxifen. In some cases, they stay on the lower dosing long term and in others, it is used as a tool to help titrate back up in case their bodies are better able to tolerate the higher dose if they get accustomed over time. I am one of those women, but it turned out I could not tolerate even 5mg.

    If sounds like your doctor has been supportive and flexible to help you stay on tamoxifen while accounting for your other health issues. Since tamoxifen has been shown to have impact even years after stopping it, it makes sense that going down to 5mg for periods of time could still be far more effective than going off completely. If you generally trust your doctor, nothing about this sets off alarm bells for me. In fact, the opposite. I would feel good about a doctor proactively working with you to help you maximize the impact of the drug while also maximize quality of life.

    That said, it never hurts to get a second opinion, even if you love your doctor and especially if you don't.

    (In the end, I went off tamoxifen and onto toremifene, a sister-SERM that is used more overseas and which I tolerated much better. Unfortunately, it did not prevent a new contralateral breast cancer occurrence, so I am now transitioning to OS/AI. Whether it did help with preventing a recurrence of the prior cancer, or I was just lucky, I will never know, so I tell myself it wasn't useless).

    We have made so much progress with breast cancer research and also there is still so much that is not known. In the end, even the best doctors have to combine their own interpretation of studies, clinical experience, collaborative knowledge, and best hunches, and even so, most of what they recommend is subject to change pending new discoveries and studies. It can be nerve-wracking for sure, for me as a patient. But I remind myself that I (and science) am still better off than I would have been ten years ago, and every year I make it longer, there is more knowledge and hope being accumulated.

    The best I think I can do is to find doctors I like/trust, and give both them and myself grace and benefit of the doubt for making the best calls we could with the information we had at the time.

    Hang in there!

  • sl43sl43
    sl43sl43 Member Posts: 10

    @gardengurl Thank you for sharing! It does help to get a look at what others have experienced/are experiencing. I hate to say it, but reading others speak about their oncs and their conversations has me a bit sad as I feel I am gaining more knowledge through secondhand accounts than directly from the horse's mouth…. Good luck to you with your lifestyle modifications - I agree with you that it seems like the best we can do is go all in and try to manipulate whatever factors are within our capabilities.

  • sl43sl43
    sl43sl43 Member Posts: 10

    @salamandra I replied earlier to your post but it somehow got zapped from the thread. In case you didn't see it, I want to repeat myself and thank you for your thorough and thoughtful reply! I am glad to hear that I am not alone in the low-dose sphere and that there are other women here who are on the same boat. It gives me some relief.

    You are right about getting a 2nd opinion. My onc seems like a nice person but frankly, a bit cavalier? I have sometimes wondered if I'm not getting careful attention because I was clinically low risk (Stage 1A, Grade 2, clear nodes, Oncotype 3) and so who cares how much Tamoxifen I take? I know well enough though, that recurrence risk exists even for early-early stagers like us, and my BCI was not ultra-low, so I feel every one of us is entitled to 100% effort and attention. It's simply frustrating bc my personality is such that when presented with a problem to solve, I throw everything at it, 1000%. To find out after 4 years that I was not technically following established guidelines for dosage, sent me in a tailspin. :/

    With that all said, I admire your gentler and more gracious attitude toward things. Some days I feel calm and optimistic, but other days I'm afraid to even feel that way bc I feel superstitious that as soon as I let my guard down, another shoe will drop. Boy, none of us signed up for this…

    Hoping the OS/AI goes over well for you… 🤞

  • zen1028
    zen1028 Member Posts: 25
    edited February 25

    @sl43sl43 May I ask what dose are you taking right now and if you have completed Tamoxifen? When you were on the 5 mg, how long was that and what SE if any you may have had? I too will need to start and just getting scared on the standard dose of 20 mg along with manufactures of tamoxifen base on other discussion boards within Normally I would try it and see, but after the experience with Lupron, I am very hesitant as Lupron is still in my system. I know I need to start, but just struggling what are the benefits on going on a drug that could impact quality of life along with work/family life, to a risk factor of 13% in 9 yrs (base on the Oncology DX score of 22 for premenopausal, stage 1A grade 2, clear margins).

  • rain88
    rain88 Member Posts: 160

    @sl43sl43 I am not sure if my account will help, as the type of cancer I was treated for was less aggressive, but I wanted to share my case anyway, to illustrate that the decisions we make, while with our medical team's help, is ultimately ours to make. I was diagnosed in 2019, as well, at age 48, perimenopausal, and started with 20 mg of Tamoxifen, which I reduced to 10 mg due to hard-to-tolerate SEs. I was able do manage on 10 mg, but, unfortunately, I had vaginal bleeding due to endometrial polyps 15 months into taking Tamoxifen, and I had to have them removed. Because of this complication, my MO - whom I liked very much for both his professional knowledge and bedside manners - took me off Tamoxifen. I thought he'd put me on AIs instead, which in the end he didn't. I wanted to stress that we had many conversations about Tamoxifen efficiency at different dosage prior to reducing it. I recall that we also discussed at the time how there wasn't sufficient data to support 5 mg for invasive breast cancer, but I remember distinctly him saying that the MOs are happier with their patients taking as little as that, as opposed to getting entirely off. Anyway, in my case, he recommended to stop additional endocrine therapy completely, if I was comfortable with that decision, which I realised that in fact I was. His recommendation was based, among others, on the benefits I'd get from hormonal therapy, which were 1% survival at 10 years and 2-3% benefit in breast cancer recurrence at 10 years. (I wonder if you talked to your MO about that.) I did my own calculations using the Breast Cancer Outcome Calculator and it did corroborate my MO's findings. As I was saying, I am now off endocrine treatment and ok with it.

    Hope this helps; best wishes going forward!

  • sl43sl43
    sl43sl43 Member Posts: 10

    Thank you so much for your input @rain88, this is exactly the kind of thing I was curious about. My doctor was extremely laid back and blase about reducing my dosage, which kind of raised a pink flag for me. He is not a numbers person, unfortunately, and seems vague in his explanations and reasonings, so it is definitely helpful even to hear from others' experiences, whatever knowledge they have about their hormone therapy.

    Thank you again, I appreciated this very much - best wishes to you as well

  • zen1028
    zen1028 Member Posts: 25

    @rain88, love that site, Breast Cancer Outcome Calculator.